Property  of 

Santa  Barbara  Medical  Library 
300  W.  Pueblo  Street 


e. 


A    TEXT-BOOK    OF 
HISTOLOGY 


A   TEXT-BOOK   OF 

HISTOLOGY 


BY 

HARVEY  ERNEST  JORDAN,  A.M.,  PH.D. 

PROFESSOR    OF    HISTOLOGY    AND    EMBRYOLOGY,    UNIVERSITY    OF   VIRGINIA 


WITH  FIVE  HUNDRED  AND  NINETY-FOUR  ILLUSTRATIONS  IN  THE  TEXT, 
AND  FOUR  PLATES 


NEW     YORK     AND     LONDON 

D.      APPLETON      AND      COMPANY 

1920 


COPYRIGHT,  1916,  1917,  1920,  BY 
D.  APPLETON  AND  COMPANY 


TO*  CTKITED  9TATEP  OF 


PREFACE 

In  the  preparation  of  this  text-book  of  Histology  we  have  kept  fore- 
most in  mind  the  needs  of  medical  students  as  we  have  come  to  under- 
stand them  in  our  experience  as  teachers  of  the  subject.  These  needs 
have  been  suggested  by  the  common  difficulties  we  have  discovered  on 
the  part  of  the  average  student.  It  has  been  our  effort  to  lessen  these 
difficulties  in  the  most  practical  way.  Our  experience  has  demonstrated 
to  us  the  efficacy  of  the  methods  here  pursued. 

The  bulk  of  the  subject  matter  of  Histology  is  now  relatively  stable. 
With  respect  to  this  nucleus  our  problem  has  largely  been  one  of  the  best 
means  of  presentation.  The  secret  of  success  in  the  acquisition  of  his- 
tologic  data  is  of  course  fundamentally  an  interest  in  the  subject.  In- 
terest can  best  be  stimulated  by  a  revelation  of  relationships  to  future 
more  clearly  conceived  practical  ends;  and  it  can  best  be  sustained  by 
the  possession  of  principles  and  generalizations  that  serve  at  least  pro- 
visionally to  coordinate  the  mass  of  seemingly  unrelated  facts.  These 
considerations  force  an  approach  to  the  subject  of  Histology  largely  from 
the  viewpoint  of  function.  The  known  or  believed  function  dependent 
upon  the  structure  described  is  therefore  briefly  indicated  whenever  this 
seems  desirable.  With  the  same  end  in  view  comparative  anatomic  and 
embryologic  facts  are  frequently  presented. 

Since  Embryology  usually  constitutes  a  separate  course  of  the  med- 
ical curriculum,  the  development  of  tissues  and  organs  is  discussed  only 
to  the  extent  deemed  absolutely  essential  for  a  proper  appreciation  of 
structure.  Since  the  anatomy  of  the  Nervous  System  likewise  properly 
constitutes  a  separate  course,  only  the  nervous  tissues  are  here  described, 
including  the  microscopic  structure  of  the  spinal  cord,  the  cerebral  cor- 
tex and  the  cerebellar  cortex.  A  description  of  the  structure  of  the 
brain  stem  is  not  included.  An  effort  has  been  made  to  include  the 
results  of  the  latest  investigations  especially  as  regards  cytologic  data, 
particularly  in  relation  to  the  genital  glands.  The  organs  of  internal 
secretion  are  treated  under  a  single  head,  and  rather  more  fully,  in  view 
of  their  now  evident  importance,  than  has  hitherto  been  the  case. 

The  illustrations  have  been  taken  from  various  sources,  duly  cred- 


PEEFACE 

ited — including  more  than  300  originals — our  one  object  having  been 
to  best  elucidate  the  structures  described.  Photomicrographs  of  actual 
sections,  combined  with  interpretive  drawings  and  diagrams,  appear  to 
us  the  ideal  illustrative  procedure. 

The  majority  of  the  photomicrographs  are  taken  from  Ferguson's 
"Normal  Histology  and  Microscopical  Anatomy."  For  a  number  we  are 
indebted  to  our  friend  and  colleague,  Professor  Albert  H.  Tuttle  of  the 
University  of  Virginia. 

An  attempt  is  made  to  adapt  the  book  somewhat  to  prevailing  non- 
uniform  demands,  by  putting  the  more  essential  and  what  we  regard  as 
additionally  desirable  in  different  type. 

Eeferences  to  the  recent  literature  are  inserted  for  the  student  who 
may  wish  to  consult  the  more  important  original  works  upon  which  the 
later  developments  of  Histology  have  advanced. 

We  gratefully  acknowledge  our  indebtedness  for  illustrations  and 
data  taken  from  the  recent  and  earlier  literature,  and  our  obligations  to 
the  publishers  for  their  kindly  help  and  courtesy. 

HARVEY  ERNEST  JORDAN 
JEREMIAH  S.  FERGUSON. 


PEEFACE  TO  THE  SECOND  EDITION 

IN  the  preparation  of  the  second  edition  I  have  been  guided  by  sug- 
gestions and  criticisms  made  by  teachers  who  have  used  the  first  edition. 
There  appears  to  be  very  general  agreement  that  the  plan  and  scope  of 
the  book  meet  the  desires  of  teachers  and  students  of  Histology  in  Medi- 
cal Schools.  The  chief  point  of  disagreement  among  teachers  concerns 
the  teaching  value  of  the  photomicrographs.  I  have  tried  to  compromise 
the  conflict  of  opinion  on  this  point  by  substituting  drawings  for  the  less 
satisfactory  photographs  of  the  first  edition.  A  number  of  new  illustra- 
tions have  also  been  added.  To  meet  the  demand  for  a  laboratory  guide, 
in  general  conformity  with  the  text,  a  chapter  has  been  added  on  "Direc- 
tions for  Laboratory  Work." 

In  the  first  edition  I  used  freely  of  the  illustrations  and  certain  por- 
tions of  the  text  in  Ferguson's  "Normal  Histology  and  Microscopical 
Anatomy."  My  indebtedness  for  this  material  was  recognized  by  publi- 
cation under  joint  authorship.  The  present  revision  has  made  the  work 
more  exclusively  my  own,  and  I  now  assume  sole  responsibility  for  the 
book  as  it  stands.  Certain  portions,  however,  still  remain  in  essentials 
as  originally  published  in  Ferguson's  excellent  book,  and  I  am  under 
deep  obligation  to  my  friend  and  former  colleague  for  this  aid  to  my 
efforts  to  produce  an  acceptable  textbook  of  Histology. 

To  all  those  who  have  in  any  way  helped,  especially  by  constructive 
criticism  and  by  the  loan  of  drawings  for  new  illustrations,  to  improve 
the  book  in  a  second  edition,  I  desire  to  express  my  gratitude.  I  am 
also  again  greatly  indebted  to  my  publishers  for  very  generous  co- 
operation in  the  work  of  revising  the  text  and  of  changing  many  illus- 
trations. 

HAKVEY  ERNEST  JORDAN. 

LABORATORY  OK  HISTOLOGY  AND  EMBRYOLOGY, 
UNIVERSITY  OF  VIRGINIA. 


CONTENTS 


CHAPTER  PAGE 

I. — INTRODUCTION — PROTOPLASM — CELL  1 

II.— EPITHELIAL  TISSUES 30 

III. — CONNECTIVE  TISSUE — CARTILAGE — BONE        ....  49 

IV.— MUSCULAR  TISSUE 90 

V.— NERVOUS  TISSUES 119 

VI. — PERIPHERAL  NERVE  TERMINATIONS — END  ORGANS  .         .         .  159 
VII.— THE  BLOOD  VASCULAR  SYSTEM                .         .         .         .         .176 

VIII.— BLOOD 203 

IX. — THE  LYMPHATIC  SYSTEM 225 

X. — Mucous  MEMBRANES — GLANDS 251 

XL— THE  SKIN .262 

XII. — THE  RESPIRATORY  SYSTEJM 292 

XIII. —THE  DIGESTIVE  SYSTEM 320 

XIV.— THE  URINARY  SYSTEM 423 

XV. — THE  REPRODUCTIVE  SYSTEM 455 

XVI.— THE  DUCTLESS  GLANDS:  ENDOCRIN  GLANDS    .         .         .         .548 

XVIL— THE  NERVOUS  SYSTEM 587 

XVIII.— THE  EYE 626 

XIX.— THE  EAR 682 

XX.— HISTOLOGIC  TECHNIC    .                                                              .  720 


LIST  OF  ILLUSTRATIONS 

riOUBK  PAGE 

1. — Various  spheroidal  cells 1 

2. — Ameba  proteus  in  motion 3 

3. — Paramecium  caudatum .4 

4. — A  generalized  cell 5 

5. — A  unicellular  flagellate  animal  (Tetramitus  chilomonas)          .         .  6 

6. — Egg  of  a  clam  (Cumingia  tellinoides) 7 

7. — Primary  spermatocyte  of  a  turtle  (Cistudo  Carolina)      ...  8 
8. — Spermatid  of  opossum  in  early  stage  of  metamorphosis  into  a  sper- 

mium 8 

9. — Cells  from  the  newly-hatched  rainbow  trout,  treated  according  to 
Meves'  technic  for  the  demonstration  of  mitochondria  (plasto- 

somes) 9 

10. — Two  cells  from  the  mesenchyma  of  the  newly-hatched  rainbow  trout  9 
11. — Intracellular  network,  or  '  trophospongium '  within  a  Purkinje  cell 

of  the  cerebellum  of  Strix  flammea 10 

12. — Diagram  illustrating  the  various  theories  of  protoplasmic  structure  11 
13. — Egg  of  the  blood  starfish  (Henricia  sanguinolenta)  in  later  growth 

period 11 

14. — Pancreas  cell  of  turtle,  filled  with  zymogenic  granules    ...  12 

15. — Motor  nerve  cell  from  the  ventral  horn  of  the  spinal  cord  of  the  ox  12 
16. — Interstitial  cell  from  the  testis  of  a  twenty-one  year  old  man. 

Showing  granular  and  filamentous  mitochondria         ...  13 
17. — A  neuron  (giant  pyramidal  cell,  or  cell  of  Betz)  from  the  cerebral 

cortex  of  man,  showing  the  neurofibrils 13 

18.— Developing  fat  cells 13 

19. — Columnar  ciliated  epithelial  cells.    Showing  canalicular  apparatus  14 
20. — Successive  stages  in  the  movement  of  an  ameba   .         ..;...         .15 

21. — A  leukocyte  from  human  blood  in  active  ameboid  motion      .         .  16 
22. — Three  cells  from  the  epididymis  of  the  rabbit        .         .         .         .16 

23.— Ciliate  and  flagellate  cells 17 

24. — Successive  steps  in  amitotic  division  in  tendon  cell  of  new-born 

mouse 18 

25. — Successive  stages  in  the  amitotic  division  of  the  ciliated  cells  lining 

the  vasa  efferentia  of  the  epididymis  of  the  mouse     .         .         .19 


x  LIST  OF  ILLUSTRATIONS 

FIGURE  PAGE 

26. — Multinucleated  giant  cell,  from  the  yolk-sac  of  a  10  mm.  pig  embryo       19 
27. — Spermatocyte  of  Pjreris  crategi,  a  butterfly,  showing  a  cilium  at- 
tached to  the  centrosome 20 

28. — Diagrams  illustrating  successive  stages  of  mitosis  .         .         .21 

29. — Cells  from  epidermis  of  the  salamander 22 

30. — Successive  stages  of  mitosis  in  the  root  tip  of  the  dogtooth  violet 

(Erythronium  americanum) 23 

31. — Successive  stages  in  the  maturation,  fertilization  and  segmentation 

of  the  star-fish  (Asterias  forbesii)  egg 26 

32. — Transverse  section  of  a  frog  embryo,  showing  the  three  germ  layers      27 
33. — Group  of  epithelial  cells  from  the  Malpighian  layer  of  the  skin         .       30 
34. — A  villus  of  the  human  placenta,  showing  a  peripheral  syncytium  of 

irregular  thickness  .         .         .         .         .         .         .         .31 

35. — Cells  from  the  pancreas  of  Necturus,  containing  secretory  granules 

and  basal  ergastoplasmic  filaments  .         .         .         .         .31 

36. — Various  forms  of  cells 31 

37. — Polyhedral  epithelium,  from  a  section  of  the  human  liver       .         .       32 
38. — Goblet  and  columnar  cells  from  the  large  intestine  of  the  cat    .         .       32 
39.— Columnar  epithelium  from  the  pyloric  region  of  the  human  stomach      33 
40. — 'Terminal  bars'  of  cement  substance  as  seen  between  the  epithelial 
cells  of  a  tubular  secreting  gland  in  the  pyloric  region  of  the 
human  stomach     .........       34 

41. — Semidiagrammatic  illustration  of  endothelium  lining  a  large  artery  37 
42. — Mesothelium  (surface  view)  from  the  mesentery  of  a  rat  .  .  38 
43. — Cuboidal  epithelium  from  the  rete  testis  of  the  rabbit  ...  39 
44. — Tip  of  a  villus  of  the  synovial  membrane  from  the  knee-joint  of  an 

old  man 39 

45. — Columnar  ciliated  epithelium  from  the  epididymis  of  a  rabbit         .       40 
46. — A  group  of  cells  from  a  transection  of  an  acinus  of  the  human  pan- 
creas; glandular  epithelium 4i 

47. — Goblet  cells  as  seen  in  a  transection  of  a  crypt  of  the  large  intestine 

in  man          .         .         .         .         .         .         .         .         .         .42 

48. — Diagram  showing  the  arrangement  of  the  columnar  and  goblet  cells 

of  figure  47 42 

49. — Stratified  epithelium  from  the  human  esophagus  ...       43 

50. — Epidermis  of  the  skin  of  the  finger  tip,  showing  extreme  keratization 

of  the  epithelium 45 

51. — Pseudostratified  columnar  ciliated  epithelium  from  a  bronchial  tube 

of  man 46 

52. — Diagram  showing  the  manner  in  which  all  the  epithelial  cells  of 
pseudostratified  ciliated  epithelium  reach  the  basement  mem- 
brane   46 

53. — Transitional  epithelium  from  a  transection  of  the  ureter  of  an  infant      47 


LIST  OF  ILLUSTRATIONS  xj 

FIGURE  PAGE- 

54. — Isolated  cells  which  may  appear  in  human  urine  ...  48 
55. — Embryonal  connective  tissue,  early  stage  .  .  .  .  .49 
56. — Embryonal  connective  tissue  at  a  later  stage  than  is  represented  in 

figure  55 49 

57. — Subcutaneous  areolar  connective  tissue  of  guinea  pig     .         .         .  50 

58. — Plasma  cells  of  connective  tissue  from  the  human  breast  .  .  51 
59. — Spindle-shaped  connective  tissue  cells  from  the  stroma  of  the  human 

ovary 51 

60. — Pigmented  cells  from  the  choroid  coat  of  the  ox's  eye    ...  52 
61. — Granule  cells  from  the  fibrous  connective  tissue  of  the  human  mam- 
mary gland   ..........  52 

62. — Gelatinous  connective  tissue  from  the  umbilical  cord  of  a  new-born 

infant 54 

63. — Reticulum  of  a  cervical  lymph  node  of  man,  from  a  thin  section  from 

which  the  lymphatic  corpuscles  had  been  partially  washed  out     .  55 
64. — Dense  fibrous  tissue  from  the  tendon  of  one  of  the  ocular  muscles  of 

a  child 57 

65. — Longitudinal  section  of  tendon  of  human  finger    .         .         .         .58 

66. — Portion  of  tendon  from  a  cow 58 

67. — Transverse  section  of  portion  of  tendon  of  human  finger         .         .  59 

68. — Piece  of  tendon  from  tail  of  white  mouse 59 

69.— Isolated  tendon  cells 60 

70. — Coarse  elastic  fibers  from  the  ligamentum  nuchae  of  the  ox    .         .60 
71. — Transection  of  a  fasciculus  of  the  ligamentum  nuchae  of  the  ox, 
showing  the  very  large  elastic  fibers  embedded  in  a  very  delicate 

network  of  collagenous  fibers 61 

72. — Portion  of  ligamentum  nuchae  of  ox    .         .         .         .         .         .61 

73. — Portion  of  a  fat  lobule  from  the  areolar  connective  tissue  surround- 
ing the  esophagus  of  a  cat 62 

74. — A  group  of  fat  cells  from  the  subcutaneous  tissue  of  a  young  rabbit  63 

75. — Fat  cells  from  a  teased  preparation  of  adipose  tissue  of  man            .  63 

76.— Adipose  tissue 64 

77. — Developing  adipose  tissue  from  the  subcutaneous  tissue  of  an  infant  64 

78. — Reticulum  from  the  mucosa  of  the  f undus  region  of  the  dog's  stomach  65 
79. — Section  through  a  small  lymph  gland  of  a  dog  .  .  .  .65 

80. — From  a  section  through  the  medulla  of  a  cervical  lymph  node  of  man  66 
81. — Transection  of  a  plate  of  hyaline  cartilage,  from  the  trachea  of  a 

child 68 

82. — Cells  and  matrix  of  hyaline  cartilage  from  the  wall  of  a  large  bronchus 

of  man          ..........  69 

83. — Elastic  cartilage  from  the  human  epiglottis,  showing  the  large  ovoid 

cartilage  cells  and  the  very  delicate  reticulum  of  elastic  fibers         .  70 
84. — Fibrocjirtilage  from  intervertebral  disk  of  ox                 .         .         .71 


Xij  LIST  OF  ILLUSTRATIONS 

FIGURE  PAGE 

85.— Notochordal  tissue 72 

86. — Transaction  through  the  compact  bony  wall  of  a  human  meta- 

carpal  bone .73 

87. — Longitudinal  section  of  ground  bone  from  the  shaft  of  the  human 

femur 74 

88. — Isolated  bone  cell  shrunk  away  from  wall  of  its  lacuna  .         .       75 

89. — An  Haversian  system,  including  the  central  canal,  several  lamellae, 

lacunae  and  canaliculi 75 

90. — Transverse  section  of  Haversian  canal,  with  contents  ...  76 
91. — The  primary  changes  in  intracartilaginous  bone  formation  .  .  80 
92. — A  longitudinal  section  of  the  two  distal  phalanges  from  the  finger 

of  a  five-months'  human  fetus 81 

93. — Reconstruction  of  cartilage  into  bone 82 

94. — Trabecula  of  primary  enchondral  bone,  showing  a  central  deep- 
staining  core  of  calcified  cartilage  and  a  peripheral  layer  of  osteo- 

blasts 83 

95. — Trabecula  of  primary  bone  from  the  finger  of  a  human  fetus  .       84 

96. — Intramembranous  bone  formation  in  the  lower  jaw  of  a  sheep  fetus      87 
97.— Smooth  muscle  cells  .         .         .         .         .         .         .         .91 

98. — Smooth  muscle  cells  from  the  pig's  stomach          ....       92 

99. — Smooth  muscle  cells  from  the  wall  of  the  human  intestine  .  .  92 
100. — Smooth  muscle  cells  from  the  wall  of  the  human  intestine  .  .  93 
101. — Two  stages  in  the  histogenesis  of  smooth  muscle,  from  the  wall  of 

the  esophagus  of  a  pig  embryo 94 

102. — A  group  of  myoblasts  from  the  heart  muscle  syncytium  of  a  48-hour 

chick  embryo 95 

103. — Cardiac   muscle   of  guinea-pig,   showing  several  branches,   cross 

striations  (ground  membranes)  and  a  number  of  intercalated  disks      95 
104. — Cardiac  muscle  cells  from  the  pig's  heart,  isolated  in  equal  parts  of 

alcohol,  glycerin,  and  water     .......       96 

105. — Cardiac  muscle  of  the  human  heart;  the  abundant  branches  are 

plainly  shown 97 

106. — The  central  portion  of  the  preceding  figure,  more  highly  magnified  .       98 
107. — Transection  of  a  group  of  cardiac  muscle  fibers  from  a  papillary 

muscle  of  the  human  heart 98 

108. — Developing  muscle  fibers  from  the  heart  of  a  human  fetus  at 

seven  months 99 

109.— Cardiac  muscle  fibers          ........     100 

110. — Diagram  of  a  striped  muscle  fiber,  according  to  Heidenhain     .          .     101 
111. — Longitudinal  section  of  portion  of  wing  muscle  fiber  of  Mantis  at 

mid-phase  of  contraction          .......      101 

112. — Longitudinal  section  of  portion  of  atrio-ventricular  bundle  of  heart 

of  beef.     Many  of  the  cells  are  binuclented      ....     102 


LIST  OF  ILLUSTRATIONS  xiii 

F1GUBE  PAGH 

113. — Longitudinal  section  of  a  trabecula  of  Limulus  (King  crab)  heart 
muscle,  showing  an  intercalated  disk  separating  a  contracted 

from  an  uncontracted  portion           ......  103 

1 14. — Semidiagrammatic  illustrations  of  various  types  of  intercalated  disks  104 

115. — Successive  stages  of  skeletal  muscle  histogenesis  in  mammals         .  105 
116. — Transverse  section  of  a  striped  muscle  fiber  of  a  newly-hatched  rain- 
bow trout,  showing  the  process  of  myofibril  increase  by  radial 

longitudinal  splitting      ........  105 

117. — Striated  muscle  fibers  ruptured  by  teasing,  showing  the  sarcolemma  106 
118. — Isolated  fragments  of  striated  muscle  fibers,  unstained  .  .  107 
119. — Striated  muscle  libers  of  the  dog,  seen  in  transection  .  .  .  107 
120. — A  portion  of  a  striated  muscle  fiber  seen  in  longitudinal  section  .  108 
121. — A  small  portion  of  a  muscle  fiber  of  a  crab  showing  beginning  separa- 
tion into  fibrils  .........  108 

122. — Fibrils  from  the  wing  muscles  of  a  wasp 109 

123. — Longitudinal  section  of  a  portion  of  a  striped  muscle  trabecula  of 

Limulus,  showing  a  nucleus  of  serrated  contour  with  the  telo- 

phragmata  attached  to  the  serrations        .         .         .         .         .  109 

124. — Striated  fiber  from  a  leg  muscle  of  the  sea  spider  (Anoplodactylus 

lentus),  showing  the  complexly  striped  condition  characteristic 

of  insect  muscle 110 

125. — Semidiagrammatic  drawing,  representing  the  appearance  of  the 
same  fiber  from  the  leg  muscle  of  a  beetle  in  ordinary  and  polarized 

light 110 

126. — Lateral  contractive  wave  of  Cassida  equestris     .         .         .         .111 

127.— Striated  muscle  fibers  of  the  dog 112 

128. — Striated  muscle  of  a  cat  seen  in  transection  .         .         .         .113 

129. — Motor  end-plate  on  an  intercostal  muscle  fiber  of  a  young  rabbit     .  115 

130. — Portion  of  a  transection  of  a  large  tendon    .....  116 
131. — Transverse  section  of  tendon  of  tail  of  adult  mouse        .         .          .116 

132. — Portion  of  a  muscle  fiber  from  the  tail  of  a  5  cm.  frog  tadpole        .  117 

133. — Diagram  of  a  neuron 120 

134. — A  unipolar  ganglion  cell  of  a  frog 122 

135. — Multipolar  ganglion  cell  from  the  ventral  horn  of  the  gray  matter  of 

the  spinal  cord  of  the  ox          .         .         .         .         .         .         .122 

136. — Pyramidal  multipolar  nerve  cell  from  the  cerebral  cortex  of  a  mouse  123 

137. — Isolated  nerve  cells  from  the  spinal  cord  of  man   ....  124 

138. — Various  types  of  nerve  cells  of  the  cerebellar  cortex      .         .         .  125 
139. — Three  types  of  nerve  cells  supplying  respectively  cardiac  (1),  smooth 

(2)  and  (3)  striated  muscle      .         .          .          .         .         .          .126 

140. — A  nerve  cell  from  the  trapezoid  nucleus  in  the  midbrain  of  a  rabbit  127 
141. — A  neuron  (giant  pyramidal  cell,  or  cell  of  Betz)  from  the  cerebral 

cortex  of  man,  showing  the  neurofibrils 128 


xiv  LIST  OF  ILLUSTRATIONS 

FIGURE  PAOE 

142. — Intracellular  network  (trophospongium)  within  a  Purkinje  cell  of 

the  cerebellum  of  Strix  flammea 128 

143.— Golgi  cell,  type  I 129 

144.^-Golgi  nerve  cell,  type  II 130 

145. — Isolated  nerve  fibers  from  a  frog 133 

146. — A  small  portion  of  a  transection  of  the  sciatic  nerve  of  a  dog    .         .134 
147. — A  group  of  large  medullated  fibers  from  a  nerve  in  the  peritracheal 

areolar  tissue  of  the  cat 134 

148.— Nerve  fibers 135 

149. — Cross  and  longitudinal  sections  of  the  same  funiculus  of  non- 
medullated  nerve  fibers  (turned  up  at  the  left),  showing  the 
perineurium  and  the  relationship  of  the  neurolemma  nuclei  to  the 

axis  cylinder  bundles  of  neurofibrils 136 

150. — Cross-section  of  the  trunk  of  the  human  vagus  nerve,  some  distance 
below  the  nodose  ganglion,  showing  medullated  and  non-medul- 

lated  fibers    .  137 

151. — Successive  stages  in  the  degeneration  process  exhibited  by  the  distal 
stump  of  a  medullated  axon  (from  sciatic  nerve  of  adult  dog)  fol- 
lowing section 138 

152. — Regenerative  stages  in  the  proximal  stump  of  the  cut  sciatic  nerve 

of  the  dog,  several  millimeters  above  the  level  of  section     .         .     139 
153. — Transection  of  the  spinal  cord  of  an  embryo  chick         .         .         .     140 
154. — Transection  of  the  spinal  cord  of  a  child,  fifth  lumbar  segment        .     141 
155. — Portion  of  gray  substance  from  the  anterior  horn  of  the  spinal  cord 
of  man,  showing  nerve  cell  bodies,  dendrons,  medullated  and  non- 
medullated  portions  of  axons,  and  neuroglia      .         .         .         .142 
156. — Transverse  section  through  the  white  substance  of  the  human  spinal 

cord 142 

157. — Neuroglia  from  the  spinal  cord  of  a  fetal  pig         ....     143 

158. — A  long-rayed  astrocyte 144 

159. — A  short-rayed  astrocyte,  or  mossy  cell 144 

160. — Neuroglia  cell  with  adjacent  fibers,  from  the  pineal  body  of  a  yearling 

sheep 145 

161. — Neuroglia  cells  and  fibers  from  the  spinal  cord  of  an  elephant         .     146 

162. — Transection  of  the  sciatic  nerve  of  a  dog 147 

163. — Diagram  of  the  origin  and  relations  of  the  peripheral  motor  and 

sensory  neurons      .........     148 

164. — Bipolar  cell  from  a  spinal  ganglion  of  a  fish  ....     149 

165. — Transformation  of  bipolar  cells  into  unipolar  cells  in  the  Gasserian 

ganglion  of  the  pig 149 

166. — Section  through  the  dorsal  root  ganglion  of  the  first  thoracic  nerve 

of  a  cat 150 

167. — A  nerve  cell  from  a  section  of  a  human  Gasserian  ganglion     .         .     150 


LIST  OF  ILLUSTRATIONS  XV 

FIGURE  PAGE 

168. — Schematic  representation  of  the  relations  of  the  structures  com- 
posing a  spinal  ganglion 151 

169. — Common  atypical,  though  probably  perfectly  normal,  nerve  cells 

from  the  spinal  ganglion  of  the  dog  .         .         .         .          .152 

170. — Sympathetic  neurons          ........  154 

171. — The  sprouting  of  an  axon  by  a  neuroblast  from  the  spinal  cord  of 

a  frog  embryo        .........  156 

172. — The  sprouting  of  an  axon  by  a  neuroblast  from  the  spinal  cord  of  a 

frog  embryo            .........  156 

173. — Nerve  endings  in  the  epithelium  of  the  larynx       ....  160 

174. — Tactile  cells  in  the  epithelium  of  the  groin  of  a  guinea-pig     .         .  160 

175. — Schematic  representation  of  a  taste  bud 161 

176. — Taste  bud  from  the  human  tongue 162 

177. — Tactile  corpuscle  of  Meissner  from  the  skin  of  the  human  toe         .  163 

178. — Tactile  corpuscle  of  Meissner      .         .         . '        .         .         .         .  164 

179. — Tactile  corpuscle  of  Meissner      .......  164 

180.— Ruffini's  end  organ 165 

181. — End  bulb  of  Krause  from  the  margin  of  the  ocular  conjunctiva       .  165 

182. — Genital  corpuscles  from  the  clitoris  of  a  rabbit      ....  166 

183. — A  lamellar  corpuscle  from  the  mesentery  of  a  cat           .         .         .  166 

184. — A  lamellar  corpuscle  from  the  pleura  of  a  child     ....  167 

185. — Lamellar  corpuscle  from  the  mesentery  of  a  kitten         .         .         .  167 
186. — A  lamellar  corpuscle  in  longitudinal  section,  showing  a  network  of 

spiral  elastic  fibers 168 

187. — Axial  section  of  a  corpuscle  of  Herbst  from  a  duck's  tongue  .          .168 

188. — A  papilla  of  the  duck's  tongue,  containing  a  corpuscle  of  Grandry  .  169 
189. — Golgi-Mazzoni  corpuscles  from  the  subcutaneous  tissue  of  the  tip 

of  the  finger 170 

190. — Motor  nerve  endings  in  striated  muscle        .....  171 

191. — A  muscle  spindle  from  the  psoas  magnus  of  man            .         .          .  172 

192. — Middle  third  of  a  terminal  plaque  in  the  muscle  spindle  of  an  adult  cat  173 

193. — Neurotendinous  end  organ  or  tendon  spindle  of  Golgi    .          .         .  174 

194. — Nerve  endings  in  cardiac  muscle,  from  the  heart  of  a  cat        .          .  175 

195. — Nerve  endings  in  smooth  muscle,  from  the  intestine  of  a  cat    .          .  175 
196. — A  small  artery  from  the  connective  tissue  of  the  anterior  cervical 

region  of  man 177 

197.— The  external  carotid  artery  of  a  child 179 

198.— Transection  of  the  wall  of  the  aorta  of  a  child       .         .         .         .179 

199. — Part  of  a  cross-section  of  the  femoral  artery  of  a  dog     .         .         .  180 

200. — Transection  of  the  celiac  axis  of  man            .....  181 

201. — A  group  of  small  blood-vessels    .......  182 

202. — Semi-diagrammatic  illustration  of  small  branch  of  pulmonary  artery 

of  ox 183 

1 


LIST  OF  1LLUSTEATTONS 

AVI 

FIGUBB  PAQE 

203.— Semi-diagrammatic  illustration  of  dividing  small  branch  of  pul- 
monary artery  of  guinea-pig 183 

204. — The  capillary  network  connecting  an  arteriole  and  venule  of  the 

omentum  of  a  young  rabbit     .         .         .         .         .         .          .185 

205.— Capillary  vessel  of  the  frog's  mesentery        .                   ...  185 

206. — Two  sinusoidal  vessels  from  the  medulla  of  the  human  adrenal       .  186 

207. — Precapillary  venule  and  arteriole 187 

208.— Transection  of  an  arteriole  and  venule 188 

209. — Transection  of  the  wall  of  the  human  vena  cava            .         ..         .  189 

210. — A  13  mm.  human  embryo 192 

21 1 .— '  Vasoformative '  cells  from  the  mesentery  of  a  rabbit  seven  days  old  193 

212. — The  parietal  layer  of  the  pericardium  of  a  child    ....  196 

213.— The  endocardium 197 

214. — Radial  sections  of  the  mitral  valve,  from  the  heart  of  a  man     .          .  198 
215. — Human  heart,  opened  from  the  right  to  show  the  atrio ventricular 

bundle  of  His 199 

216. — Reconstruction  of  the  sino ventricular  system  (bundle  of  His)  of 

the  calf 's  heart 200 

217. — Oxalated  plasma  of  human  blood  clotted  with  thrombin,  showing 

fibrin  needles 204 

218. — From  a  freshly  prepared,  unstained  specimen  of  human  blood         .  205 

219. — Blood  cells  from  a  specimen  of  freshly  drawn  unstained  human  blood  206 

220. — Showing  the  action  of  water  upon  the  red  blood  corpuscle      .          .  206 

221. — Five  nucleated  red  cells  (erythrocytes)  from  the  blood  of  a  frog       .  207 
222. — Three  nucleated  red  blood  cells  (erythrocytes)  from  the  marrow  of  a 

human  rib • 207 

223. — A  group  of  cells  from  normal  human  blood            ....  208 

224. — A  group  of  blood  platelets,  from  the  human  blood          .         .         .  209 
225. — Outline  drawings  of  living  polymorphonuclear  leukocytes  of  rabbit, 
from  a  drop  of  blood  mixed  with  Ringer's  solution  to  which  a 

small  amount  of  hirudin  had  been  added  to  prevent  coagulation    .  211 
226. — Section  of  bone  marrow  from  skull  of  25  mm.  turtle  embryo  (Chely- 

dra  serpentina),  showing  three  main  stages  in  the  hemopoiesis     .  212 

227.— Hemoglobin  crystals 213 

228. — Crystals  of  chlorid  of  hematin  or  hemin 213 

229. — Wall  of  yolk  sac  of  a  13  mm.  human  embryo  (Fig.  210),  showing  a 
small  blood  island  and  several  small  blood  vessels  contain- 
ing erythrocytes .  .  215 

230. — Large  blood  island  from  yolk  sac  of  a  13  mm.  human  embryo         .  216 
231. — Diagrammatic  illustrations  of  successive  stages  in  the  transforma- 
tion of  the  mammalian  erythrocyte  to  form  the  erythroplastid     .  218 
232. — Successive  stages  in  the  elimination  of  the  erythroblast  nucleus, 

from  homoplastic  cultures  of  blood  of  a  32  mm.  pig  embryo         .  218 


LIST  OF  ILLUSTRATIONS  xvii 

FIGURE  PAGE 

233. — From  a  section  of  red  marrow  of  a  human  bone    ....  220 
234. — Types  of  cells  from  a  smear  preparation  of  the  marrow  of  a  human 

rib 221 

235. — Subcutaneous  lymphatic  vessel  of  a  fetal  pig         .          .         .         .  227 

236. — The  growing  end  of  a  developing  lymphatic  vessel  in  the  subcutane- 
ous tissue  of  a  fetal  pig            .......  228 

237. — Lymphatic  and  blood  vessels  in  the  hilum  of  a  human  lymph  node   .  229 
238. — Lymphatic  capillary  from  the  spermatic  cord  of  a  dog,  showing  nerve 

endings 230 

239. — Transection  of  the  pericardium  of  a  child 232 

240. — Section  of  a  vascular  synovial  villus   from  the  knee  joint  of  a 

child .233 

241. — A  lymph  nodule,  solitary  follicle,  from  the  large  intestine  of  man     .  234 

242. — Diagrammatic  illustration  of  a  lymph  node           ....  236 

243. — Transection  of  a  cervical  lymph  node  of  a  dog      ....  237 

244. — Transection  of  a  mesenteric  lymph  node  of  a  man          .         .         .  237 

245. — Diagram  of  the  blood  vessels  of  a  lymph  node      ....  238 

246. — Section  of  human  hemolymph  node  (" splenolymph  gland")   .          .  240 

247. — Horizontal  section  through  the  faucial  tonsil  of  a  child  .         .         .  241 

248. — From  a  crypt  of  a  dog's  tonsil 243 

249.— The  lingual  tonsil  of  man 244 

230. — Portion  of  spleen  of  cat,  showing  capsule  (above  and  at  left)  and 

five  splenic  nodules        ........  246 

251. — Diagram  of  a  lobule  of  the  spleen 247 

252. — The  origin  of  a  vein  in  the  splenic  pulp 248 

253. — Types  of  cells  from  a  smear  preparation  of  the  pulp  of  the  human 

spleen 249 

254. — Diagram  of  a  mucous  membrane  having  simple  tubular  glands        .  252 

255. — Diagrams  of  the  principal  types  of  glands 253 

256. — Transection  of  three  secreting  tubules  of  the  submaxillary  gland  of 

man 255 

257. — Model  of  a  reconstruction  of  the  lacrimal  gland  of  man          .         .  258 
258. — Reconstruction  of  a  mucous  gland  from  the  respiratory  region  of  the 

nasal  mucosa  of  a  child 259 

259. — Reconstruction  of  an  intralobular  duct  dividing  into  its  terminal 

intercalary  ducts  and  acini 259 

260.— Epidermis  of  the  foot -.263 

261. — Section  of  thin  skin  from  abdomen  of  negro,  showing  the  distribu- 
tion of  the  pigment  granules  in  dermal  and  epidermal  cells          .  264 
262. — Section  of  thin  skin  from  abdomen  of  light  brown  mulatto     .         .  264 
263. — Skin  from  sole  of  human  foot,  showing  spiral  ducts  of  two  sweat 

glands  opening  through  the  epidermis       .....  266 

264. — Transection  of  the  epidermis  of  the  foot       .....  267 


xviii  LIST  OF  ILLUSTRATIONS 

FIGURE  PAGE 

265. — Three  early  stages  in  the  histogenesis  of  the  skin  .  „  .  270 

266. — From  a  section  of  the  abdominal  integument -of  an  infant  .  .  272 

267. — Several  coils  of  a  sudoriparous  gland  of  the  human  finger  .  .  273 

268. — Terminal  phalanx  of  finger  of  human  fetus  ....  275 

269. — Transection  through  the  margin  of  a  finger  nail  ....  276 
270. — Longitudinal  vertical  section  of  the  young  nail  and  nail-bed  of  an 

infant 277 

271. — Five  stages  in  the  development  of  a  human  hair  .  .  .  278 
272. — From  a  section  of  the  skin  of  an  infant's  arm,  showing  small  im- 
mature hair  follicles  in  transection 280 

273. — From  a  section  of  the  human  scalp 282 

274. — Transection  of  a  hair  near  the  middle  of  the  root  sheath  .  .  284 

275. — Regeneration  of  a  hair 287 

276.— Sebaceous  glands  in  the  scalp  of  a  child 288 

277. — Section  of  a  sebaceous  gland  from  the  human  scalp,  through  point 

of  opening  into  a  hair  follicle  (obliquely  cut)  ....  289 
278. — Cells  from  the  central  portion  of  figure  277,  showing  two  successive 

stages  in  sebum  formation  by  process  of  fatty  metamorphosis  of 

the  cytoplasm .  .  289 

279. — Reconstruction  of  the  cutaneous  blood  vessels  ....  290 
280. — Photograph  of  Azoux  model,  showing  nostril,  pharynx,  larynx  and 

related  structures 292 

281. — From  a  section  of  the  mucous  membrane  of  the  respiratory  region 

of  the  human  nose          ........  294 

282.— The  olfactory  mucosa  of  a  cat  .  .  .  _.  .  .  .  296 

283. — The  olfactory  mucous  membrane 297 

284. — Vertical  section  of  the  olfactory  mucosa  of  a  kitten  .  .  .  298 
285. — Diagram  of  the  relations  of  the  neurons  of  the  olfactory  nerve  and 

olfactory  bulb 299 

286. — A  vertical  section  through  the  lateral  wall  of  the  human  larynx  .  301 

287. — Transection  of  the  wall  of  a  child's  trachea  ....  302 
288. — Mucus-secreting,  tubulo-alveolar  gland  of  the  human  tracheal 

mucosa 303 

289. — A  bronchus  from  the  human  lung 305 

290. — Diagram  of  primary  lobule  of  lung  (lung  unit)  ....  307 

291. — From  a  section  of  a  child's  lung 308 

292.— From  a  section  of  a  child's  lung 309 

293.— From  a  section  of  a  child's  lung 310 

294. — Diagram  of  the  three  pulmonary  lobules  connected  with  a  terminal 

bronchiole 311 

295.— Two  alveoli  of  a  child's  lung .312 

296. — Transection  of  the  pleura  of  an  infant 313 

297. — From  a  section  of  the  pleura  of  man  ......  313 


LIST  OF  ILLUSTRATIONS  xjx 

FIGURE         '  PAGE 

298.— From  the  lung  of  a  child 315 

299. — From  the  lung  of  a  dog  whose  blood  vessels  had  been  injected  with 

a  gelatinous  mass,  and  appear  black  .  .  .  .  .316 

300. — From  the  central  portion  of  figure  299 317 

301. — From  a  section  through  the  lip  of  an  infant  .  .  .  .321 

302. — Axial  section  of  a  human  molar  tooth 322 

303. — Diagram  of  an  axial  ground  section  of  tooth,  showing  the  several 

stripes  of  the  clentin  and  the  enamel 323 

304. — From  a  longitudinal  section  of  the  neck  of  a  child's  tooth  and  the 

adjacent  alveolus 324 

305. — From  a  section  of  a  human  tooth  which  had  been  ground  to  extreme 

thinness         ..........  325 

306. — Section  of  fang  parallel  to  the  dentinal  tubules,  human  canine  .  326 
307. — Dentin  from  a  ground  section  of  a  human  mclar,  showing  the  den- 
tinal tubules  cut  across 327 

308. — Enamel  prisms  in  transection 328 

309. — A  group  of  enamel  prisms  cut  longitudinally,  from  the  incisor  tooth 

of  the  rat,  showing  their  irregularly  beaded  character  and  the  cross 

striations       ..........  329 

310. — From  a  section  of  a  human  tooth  which  had  been  ground  to  extreme 

thinness 330 

311. — Developing  tooth  from  a  human  embryo  17  mm.  long  .  .  331 

312. — Dental  anlages  from  a  human  fetus  40  mm.  long  .  .  .  332 
313. — Two  stages  in  the  early  development  of  the  teeth,  from  a  25  mm.  pig 

embryo 332 

314. — Developing  tooth  from  a  human  fetus  30  cm.  long  .  .  .  333 

315. — A  developing  tooth  from  an  infant's  jaw  .  .  .  .  .  334 

316. — A  portion  of  Fig.  315,  near  the  apex  of  the  developing  tooth  .  335 

317. — Odonto  blasts  and  dentin  of  the  tooth  of  a  new-born  cat  .  .  336 
318. — View  of  dorsum  of  tongue,  showing  the  various  papillae,  the  tonsils 

and  the  fauces  .  .  . 338 

319. — One  lateral  half  of  a  coronal  section  of  a  dog's  tongue   .         .         .  339 

320. — Filiform  papilla?  of  the  dog's  tongue   ......  340 

321. — A  filiform  and  a  fungiform  papilla,  from  an  injected  specimen  of 

tongue  of  cat 341 

322. — Circumvallate  papillae  of  the  human  tongue  ....  342 
323. — Two  foliate  papillae  from  a  rabbit's  tongue,  showing  numerous 

taste  buds  along  their  lateral  margins 343 

324. — Diagram  of  the  alimentary  canal  of  man 345 

325. — Surface  view  of  Auerbach's  intramuscular  nerve  plexus,  from  the 

esophagus  of  a  cat          ........  346 

326. — Longitudinal  section  through  region  of  transition  from  esophagus 

(right)  to  cardiac  end  of  stomach  (left)    .....  349 


XX  LIST   OF   ILLUSTRATIONS 

FIGURE  PAGE 

327. — Transverse  section  of  human  esophagus  through  lower  third  .         .  350 
328. — From  a  section  of  the  human  esophagus      .          .         .         .         .351 

329. — Section  through  the  stomach  wall  of  man  (pyloric  region)       .         .  352 

330. — The  mucosa  of  the  fundus  region  of  the  dog's  stomach            .         .  354 

331. — Longitudinal  section  of  the  fundus  glands  of  man          .         .         .  355 
332. — Transections  of  three  glands  of  the  fundus  region  of  the  human 

stomach 356 

333. — A  pyloric  gland,  from  section  of  the  dog's  stomach        .         .         .  357 

334. — Portion  of  gastric  gland  from  the  fundus  region  of  the  stomach       .  357 

335. — Secretory  capillaries  of  the  fundus  glands  of  the  dog's  stomach       .  358 

336. — The  mucosa  of  the  pyloric  region  of  the  human  stomach        .          .  359 

337. — Blood  vessels  and  lymphatics  of  stomach 361 

338. — Termination  of  sympathetic  nerve  fibers 362 

339. — Schematic  diagram  illustrating  probable  relationship  of  sympathetic 

neurons  in  myenteric  and  submucous  plexuses            .         .         .  363 
340. — Section  through  the  commencement  of  the  duodenum  at  the  pylorus  364 
341. — From  a  longitudinal  section  through  the  duodenum  of  a  cat            .  365 
342. — The  central  portion  of  a  Peyer's  patch  in  the  ileum  of  a  dog's  in- 
testine             367 

343. — Diagram  of  small  intestine,  showing  the  topographical  relationship 

of  the  intestinal  glands  (crypts  of  Lieberkiihn)  to  the  villi    .         .  368 

344. — Longitudinal  section  of  villus 369 

345. — Several  villi  from  the  small  intestine  of  the  dog,  in  longitudinal 

section 370 

346. — Reconstruction  model   of  a   Brunner's  gland,   from  the   human 

duodenum 372 

347. — The  blood-vessels  of  the  small  intestine  of  a  dog,  drawn  after  an 

injected  preparation        ........  373 

348. — Intestinal  mucosa  of  a  frog  during  the  absorption  of  fat          .          .  375 
349. — Apex  of  an  intestinal  villus  of  a  rabbit  which  had  been  fed  with 

milk 376 

350. — Section  of  large  intestine  of  dog,  showing  intestinal  glands  (crypts 

of  Lieberktihn)  cut  longitudinally 378 

351. — Section  of  portion  of  large  intestine  of  dog,  showing  the  intestinal 
glands  (crypts  of  Lieberkiihn)  cut  across,  their  lining  including 

columnar  and  goblet  cells 379 

352. — Transection  of  the  vermiform  appendix  of  man     ....  380 
353. — Semidiagrammatic  representation  of  a  small  mucous  gland  from  the 

oral  mucosa  of  a  rabbit 382 

354. — Corrosion  model  of  an  interlobular  duct  and  its  branches,  from  the 

human  submaxillary  gland 383 

355. — Intercalary  ducts  and  acini  of  the  human  submaxillary  gland,  corro- 
sion model 385 


LIST    OF    ILLUSTRATIONS 


356. — A  group  of  mucous  acini,  from  the  human  subma'xillary  gland           .  386 

357. — From  the  sublingual  gland  of  man        ......  387 

358. — Mucous  acini  of  the  retrolingual  gland  of  the  rat    ....  388 

359. — Diagram  of  the  arrangement  of  the  cells  in  a  mixed  salivary  gland  389 
360. — Diagrams  of  A,  parotid  gland;  B,  submaxillary  gland;  C,  sublingual 

gland;  and  D,  pancreas 389 

361. — From  a  section  of  the  human  parotid  gland           .         .         .         .  390 

362. — From  a  section  of  the  human  submaxillary  gland           .         .         .  391 

363. — Reconstruction  model  of  the  sublingual  gland  of  man    .         .         .  392 

364. — Nerve  endings  in  a  salivary  gland 393 

365. — Early  stages  in  the  development  of  the  pancreas,  illustrating  condi- 
tions in  the  5  and  7  weeks  old  human  embryos           .          .         .  394 
366. — From  a  section  of  the  human  pancreas,  showing  several  lobules  and 

the  broad  interlobular  bands  of  connective  tissue       .          .         .  395 
367. — Drawing  of  an  intercalary  duct  with  three  branches  ending  in  acini 

to  form  centro-acinial  cell  groups     .         .         .         .         .         .  396 

368. — Reconstruction  model  of  the  human  pancreas        ....  396 

369. — Acini  of  the  human  pancreas       .......  397 

370. — Pancreatic  acinus  of  cat  cut  transversely  near  fundus,  showing  the 

basal  (prozymogen)  filaments  of  the  cells           ....  398 

371. — Cells  from  pancreas  of  Necturus 399 

372. — Two  adjacent  acini  from  the  guinea-pig's  pancreas         .         .         .  399 
373. — Section  of  an  acinus  from  the  guinea-pig's  pancreas,  showing  the 

basal  mitochondrial  content  and  the  central  zymogen  granules     .  400 
374. — Intercalary   duct   with   branches,    from    pancreas   of   guinea-pig, 
showing  highly  branched  tubules  connected  with  the  duct  and 

with  the  islet          . 400 

375.— Pancreatic  islet 401 

376. — From  the  human  pancreas 402 

377. — Section  of  a  pancreatic  islet  from  injected  specimen  of  cat's  pancreas 

to  show  the  profuse  blood  supply     ......  404 

378. — A  lobule  of  the  pig's  liver;  the  central  vein  lies  in  the  middle  of  the 

figure 405 

379. — Diagram  of  liver  lobules,  the  upper  two  cut  transversely,  the  lower 

longitudinally         .........  406 

380. — From  a  section  of  the  turtle's  liver,  showing  the  tubular  arrange- 
ment of  the  parenchyma          .......  407 

381.— The  reticulum  of  the  dog's  liver 408 

382.— Stellate  cells  of  von  Kupffer  in  the  liver  of  a  dog  .         .         .409 

383. — A  lobule  of  the  pig's  liver  in  longitudinal  section,  showing  the  rela- 
tion of  the  central  and  sublobular  veins  and  the  arrangement 

of  the  hepatic  cells 410 

384. — A  lobule  of  the  human  liver,  seen  in  transection   .         .         .         .411 


xxjj  LIST  OF  1LLUSTKAT1ONS 

FIGURE  PAGE 

385.— Section  of  liver  tissue  showing  the  liver  cell-cords,  and  the  sinusoids 

lined  with  endothelium .412 

386. — Diagram  of  four  adjacent  liver  cells 413 

-{87. — Isolated  lobules  oi  the  pi^s  uvo.  .  .  413 
388. — Showing  the  connection  between  the  intralobular  and  interlobular 

bile  ducts  in-  the  cat's  liver 414 

389. — Types  of  cells  from  a  section  of  the  normal  human  liver         .         .414 
390. — Human  liver  cells,  showing  enlarged  intracellular  canaliculi,  a  con- 
dition characteristic  of  jaundice       .         .         .         .         .         .415 

391. — Diagram  of  a  portal  canal,  including  a  branch  of  the  portal  vein, 
hepatic  artery,  hepatic  (bile)  duct,  lymphatic  and  non-medul- 

lated  nerve  trunks 415 

392. — From  a  section  of  the  rabbit's  liver  whose  blood  vessels  had  been 
injected  with  a  carmin  stained  gelatin  mass;  somewhat  more  than 

a  single  lobule  is  represented 416 

393. — A  group  of  surface  lobules  of  the  pig's  liver  ....  418 
394.— Intralobular  nerve  fibers  in  a  rabbit's  liver  .  .  .  .420 
395.— From  a  section  through  the  wall  of  a  dog's  gall-bladder  .  .421 
396.— Reconstruction  of  the  wall  of  a  dog's  gall-bladder  .  .  .421 

397. — Longitudinal  section  of  kidney 424 

398.— Diagram  of  the  structure  of  the  kidney 425 

399. — Reconstruction  of  a  uriniferous  tubule  of  an  infant        .         .         .  426 

400. — Diagram  of  uriniferous  tubule  of  a  mammal          ....  428 

401. — Reconstruction  of  a  glomerulus  of  the  human  kidney     .         .         .  429 

402. — From  the  cortical  labyrinth  (pars  convoluta)  of  the  human  kidney  430 
403. — From  the  cortex  of  the  human  kidney,  showing  a  transection  of  a 

cortical  ray  in  the  lower  left-hand  corner           ....  432 
404.— From  a  longitudinal  section  of  a  convoluted  tubule  of  the  guinea- 
pig's  kidney 433 

405. — Cross  section  of  a  proximal  convoluted  tubule  from  the  kidney  of 
a  mouse,  showing  basal  filaments  breaking  up  into  granules  cen- 
trally, and  the  central  striated  border  of  the  cells     .         .         .  433 
406. — A  group  of  tubules  from  a  transection  of  a  renal  pyramid  of  the 

human  kidney;  the  section  passes  through  the  boundary  zone     .  439 

407.— The  distribution  of  the  left  renal  artery 441 

408. — From  the  cortex  of  the  human  kidney 442 

409. — Nerve  endings  in  a  convoluted  tubule  of  the  frog's  kidney      .         .  444 

410. — Cast  of  the  pelvis,  infundibula  and  calices  of  the  kidneys  of  a  man   .  445 

411. — Transection  of  human  ureter 446 

412. — Transitional  epithelium  of  dog's  ureter 447 

413. — Tranverse  i-ection  of  urinary  bladder  of  dog         ....  449 

414. — The  mucosa  of  a  child's  bladder  in  the  contracted  state  of  the  organ  450 

415. — Transitional  epithelium  of  dog's  bladder 451 


LIST  OF  ILLUSTRATIONS  xxiii 

FIGURE  PAGE 

416.— Epithelial  cells  from  the  bladder  of  the  rabbit      .         .         .         .452 

417. — Transection  of  the  female  urethra 453 

418. — Diagram  of  a  male  genitalia  (adapted  from  Mcrkel)       .         .         .  455 

419.— Diagram  of  female  internal  genitalia 456 

420. — Diagrams  illustrating  the  metamorphoses  of  the  indifferent  urogeni- 

tal  system  into  the  male  and  female  systems     ....  457 
421. — Diagrams  illustrating  the  process  of  maturation  in  the  male  and 

female  gametes 462 

422. — Primary  spermatocyte  of  a  grasshopper,  Hippiscus  tuberculatus, 
showing  the  compact  accessory  chromosome  among  the  paler 

mossy  prophase  euchromosomes,  and  the  idiosome     .         .         .  464 

423. — Chromosome  groups  of  Schistocerca  damnifica      .         .         .         .  473 
424. — Diagram  illustrating  the  behavior  of  the  chromosomes  during  the 

first  and  second  maturation  divisions 474 

425. — The  testicle  with  its  system  of  efferent  passages    ....  480 

426. — Seminal  tubule  of  a  man  in  transection 481 

427.— Sertoli  cells  of  the  human  testis 482 

428. — Portion  of  a  transection  of  a  seminiferous  tubule  from  the  human 

testis,  illustrating  the  various  stages  in  spermatogenesis      .         .  483 
429. — Successive  stages  in  the  metamorphosis  of  the  spermatid  into  the 

spermatozoon         .........  484 

430. — Diagram  of  human  spermatozoon        ......  485 

431. — Spermatozoa  of  various  animals 486 

432. — Spermatozoa  from  the  semen  of  man 487 

433 . — A  group  of  interstitial  cells  from  the  testis  of  a  thirty-five  year  old  negro  488 

434. — Interstitial  cells  from  the  human  testis 489 

435. — A  small  portion  of  the  wall  of  an  efferent  ductule  of  the  testicle  .  491 
436. — Efferent  ductules  of  the  rabbit's  epididymis  ....  491 
437. — Several  coils  of  the  rabbit's  epididymis  in  transection  .  .  .  492 
438. — Transection  of  the  ductus  deferens  of  a  dog  ....  494 
439. — From  a  section  through  the  wall  of  a  seminal  vesicle  of  man  .  495 
440. — Model  of  a  reconstructed  prostate  gland  of  man  ....  496 
441. — Several  alveoli  of  the  human  prostate  gland,  seen  in  section  .  498 
442. — Portion  of  prostate  gland  of  an  old  man,  showing  the  prostatic  con- 
cretions    499 

443. — Prostatic  genital  corpuscles 500 

444. — Reconstruction  of  a  bulbo-urethral  (Cowper's)  gland  of  man           .  501 

445. — From  a  section  of  the  bulbo-urethral  (Cowper's)  gland  of  man        .  501 
446.— Transection  of  a  child's  penis,  just  back  of  the  glans     .         .         .503 

447. — Helicine  artery  in  section,  from  the  urethral  bulb  of  man       .         .  504 

448. — The  erectile  tissue  of  the  penis             505 

449. — Section  of  ovary  of  adult  cat,  showing  five  vesicular  (Graafian)  folli- 
cles, four  with  the  cumulus  oophorus  and  the  enclosed  ovum         .  508 


XXIV  LIST  OF  ILLUSTBATIONS 

FIGURE  PAGE 

450. — From  the  ovarian  cortex  of  an  infant,  showing  many  ova  in  the 

primary  follicular  stage 509 

451. — Ovum,  containing  a  yolk  nucleus  ('Dotterkern')  at  the  left  and  above 

the  nucleus 511 

452. — From  a  section  of  the  ovarian  cortex  of  a  new-born  kitten      .          .  513 

453. — A  primary  ovarian  follicle  of  the  human  ovary      ....  514 

454. — A  vesicular  (Graafian)  follicle  of  the  human  ovary,  somewhat  more 

advanced  than  the  preceding  .         .         .         .         .         .515 

455. — A  nearly  ripe  Graafian  follicle  from  the  ovary  of  a  dog  .          .516 

456. — Photomicrograph  of  a  section  of  cat's  ovary,  showing  two  primary 

follicles  and  one  vesicular .517 

457. — Section  through  the  peripheral  portion  of  a  corpus  luteum,  showing 

lutein  cells    .         . 520 

458. — Portion  of  corpus  luteum  of  rabbit 521 

459. — A  corpus  albicans,  from  a  section  of  the  human  ovary            .         .  522 

460.— From  a  thick  section  of  the  ovary  of  a  woman      ....  523 

461. — Transections  of  the  human  oviduct 524 

462. — From  a  transection  of  the  ampulla  of  the  oviduct,  showing  the  struc- 
ture of  the  mucosa          ........  525 

463. — Transection  of  the  uterus  of  an  ape     ......  527 

464. — Transection  through  the  body  of  the  human  uterus       .         .         .  529 

465. — From  a  transection  of  the  uterine  mucosa    .....  530 

466. — From  the  cervix  uteri  of  a  girl  of  sixteen  years,  showing  the  cervical 

glands  in  section 531 

467. — A  gland  of  the  human  cervix  uteri  in  longitudinal  section       .          .  532 
468. — From  a  section  of  the  human  uterine  mucosa  at  the  first  day  of  men- 
struation      ..........  534 

469. — A  group  of  decidual  cells  from  the  human  uterus  during  the  early 

stages  of  pregnancy        .         .         .         .         .         .         .         .  535 

470. — Chorionic  villi  from  the  human  placenta  at  full  term     .         .          .  536 

471. — Chorionic  villus  at  various  stages  of  development          .         .         .  537 

472.— Vaginal  mucosa 538 

473. — Transection  of  a  labium  minus  of  an  infant           ....  540 

474. — From  the  actively  secreting  mammary  gland  of  a  woman       .          .  542 
475. — Model  of  a  reconstruction  of  an  intralobular  duct  and  its  acini  from 

the  active  mammary  gland  of  a  woman 543 

476. — Active  mammary  gland  of  rabbit  (22  days  after  fecundation). 

The  alveoli  are  filled  with  milk  containing  fat  droplets      .          .  544 

477. — From  a  section  of  the  human  mammary  gland  in  the  resting  condition  545 

478. — From  a  section  through  the  human  adrenal           ....  550 

479. — Photomicrograph  of  suprarenal  gland  of  dog         ....  551 
480r — More  highly  magnified  region  of  the  preceding  section,  to  show  the 

capsule,  zona  glomerulosa,  and  a  portion  of  the  zona  fasciculata  .  552 


LIST  OF  ILLUSTRATIONS  xxv 

FIGURE  PAGE 

481. — Reconstruction  of  a  dog's  adrenal 555 

482. — Section  of  part  of  an  accessory  suprarenal  (chromophil  body),  new- 
born child     556 

483. — From  a  section  of  the  human  thyroid  gland  ....     558 

484. — Diagram  of  pharynx  of  human  embryo  showing  the  origins  of  the 

anlages  of  the  thymus,  thyroid  and  parathyroids  (epithelial  bodies)  560 
485. — From  the  border  of  a  mass  of  aberrant  thyroid  tissue  of  man,  occur- 
ring in  the  region  of  the  parathyroid  glands  ....  562 
486. — Human  parathyroid  tissue,  moderately  magnified  .  .  .  564 
487. — A  section  through  several  lobules  of  the  thymus  of  an  infant  .  .  566 
488. — A  thymic  corpuscle  from  the  thymus  of  an  infant  .  .  .  567 

489. — Carotid  gland  of  an  ape 569 

490. — From  a  section  of  the  coccygeal  gland  of  man       ....     570 
491. — Median  section  through  the  anlages  of  the  hypophysis  cerebri  of  a  10 

mm.  cat  embryo 571 

492. — Sagittal  view  of  a  wax  reconstruction  of  the  hypophysis  cerebri  of 

the  adult  cat 574 

493. — Pars  tuberalis,  hypophysis  of  cat 576 

494. — Pars  infundibularis,  hypophysis  of  cat          .....     576 

495. — Pars  distalis,  hypophysis  of  cat 577 

496. — Section  of  hypophysis  cerebri  of  dog,  showing  portions  of  pars  distalis 
of  anterior  or  buccal  lobe,  residual  lumen,  pars  tuberalis  (pars 
intermedia),  pars  neuralis,  and  capsule     .....     578 
497. — Field  from  the  center  of  a  normal  canine  (puppy)  pars  anterior       .     579 
498. — Semidiagrammatic  representation  of  a  median  longitudinal  section 

through  the  epiphysis  of  a  17  cm.  sheep  fetus    ....     581 
499. — Cells  from  the  pineal  body  of  a  11  cm.  sheep  fetus         .         .         .     582 
500. — Photomicrograph  of  a  peripheral  portion  of  the  pineal  body  of  a  21 
cm.  sheep  fetus,  showing  several  cysts  and  vascular  trabeculae, 
and  an  enormous  number  of  intracellular  melanic  granules  •        .     583 
501. — Photomicrograph  of  peripheral  region  of  pineal  body  of  a  yearling 
sheep,  to  show  the  character  of  the  parenchyma,  the  neuroglia  cells 

and  fibers,  and  the  interneuroglia  cells 584 

502. — Two  neuroglia  and  three  interneuroglia  cells  from  the  pineal  body 

of  a  lamb 584 

503. — Cells  from  pineal  of  yearling  sheep      .  .         .         .         .     585 

504. — Section  of  pineal  body  of  an  old  sheep,  showing  'brain  sand'  (acer- 

vulus)  in  the  parenchyma 586 

505. — Human  embryo  2  millimeters  long 587 

506. — Transection  through  the  Graf  Spee  embryo  shown  in  figure  505         .     588 
507. — Three  successive  stages  in  the  process  of  closure  of  the  medullary 
(neural)  groove  to  form  the  medullary  (neural)  canal  and  neural 
(ganglionic)  crests 588 


xxvi  LIST  OF  ILLUSTRATIONS 


508. — Cell  lining  the  neural  canal  of  the  newly-hatched  rainbow  trout, 

showing  mitochondria  in  an  embryonic  nerve  cell       .         .         .  589 

509. — Section  through  medullary  plate  of  a  rabbit  embryo      .         .         .  589 
510. — Section  through  medullary  plate  of  closing  neural  groove  of  rabbit 

embryo 590 

511. — Section  through  wall  of  later  neural  tube  of  rabbit  embryo,  showing 
a  stage  in  the  differentiation  of  the  ependyma  cells  and  the  forma- 
tion of  a  myelospongium         .......  590 

512. — Section  of  wall  of  forebrain  of  four-day  chick  embryo    .         .         .  591 
513. — Diagram  of  a  transection  of  the  spinal  cord  of  an  early  embryo,  show- 
ing the  migration  of  neuroblasts  toward  the  marginal  veil,  and 

the  ventral  nerve  root .         .591 

514. — Transection  of  the  spinal  cord  of  a  human  embryo  of  four  weeks    .  592 

515. — Transection  of  the  spinal  cord  of  an  embryo  chick         .         .         .  593 
516. — Reconstruction  of  the  anterior  portion  of  the  body  of  a  chick,  the 

head  distinctly  differentiated,  seen  from  the  surface            .         .  593 

517. — Transection  of  the  spinal  cord  of  a  child,  seventh  cervical  segment     .  595 

518. — Diagram  of  the  fiber  paths  of  the  spinal  cord        ....  518 

519. — Transection  of  the  spinal  cord  of  a  child,  third  sacral  segment         .  600 

520. — Transection  of  the  spinal  cord  of  a  child,  fifth  lumbar  segment        .  600 

521. — Transection  of  the  spinal  cord  of  a  child,  eighth  thoracic  segment  .  601 

522. — Transection  of  the  spinal  cord  of  a  child,  fourth  cervical  segment   .  604 

523. — Median  sagittal  section  through  the  brain 605 

524. — From  a  section  of  the  cerebellar  cortex  of  man      ....  606 

525. — A  Purkinje  cell  from  the  human  cerebellar  cortex           .         .         .  607 

526. — A  Purkinje  cell  from  the  cerebellar  cortex  of  the  rabbit          .         .  608 

527.— Diagram  of  the  cerebellar  cortex 610 

528. — Left  lateral  surface  view  01  cerebral  cortex  in  man,  showing  the 

lobes,  main  sulci,  and  the  larger  functional  areas        .         .         .  612 

529.-  -Large  pyramidal  cell  of  the  cortex 613 

530. — Scheme  of  the  motor  area  of  the  cerebral  cortex,  showing  the  effect 

of  various  staining  methods     .          .         .         .         .         .         .614 

531. — Disposition  of  the  nerve  fibers  in  the  cerebral  cortex  of  man     .         .  615 

532. — Human  cortex  cerebri,  motor  area 616 

533. — Human  cortex  cerebri,  parietal  lobe 617 

534. — Human  cortex  cerebri,  olfactory  region         .         .         .         .         .619 
535. — Section  of  the  spinal  cord  and  its  membranes,  from  the  upper  thoracic 

region 621 

536. — Dissection  of  eyelids  and  lacrimal  apparatus         ....  626 

537. — Horizontal  section  of  the  right  eyeball 627 

538. — The  anterior  segment  of  a  child's  eye;  meridional  section       .         .  629 

539. — From  a  meridional  section  of  the  human  cornea    ....  630 

540. — Corneal  corpuscles  of  the  frog     ....                           .  632 


LIST  OF  ILLUSTRATIONS 

FIGURE  PA3E 

541.— Corncal  cells,  isolated 633 

542. — From  a  meridional  section  of  the  choroid  coat       ....  637 

543. — The  ciliary  body  and  the  adjacent  structures;  meridional  section    .  639 

544. — The  developing  eye  in  meridional  section;  diagrammatic         .          .  645 

545. — Schematic  reconstruction  of  the  developing  eye     ....  646 

546. — The  retina  of  a  child's  eye;  meridional  section       .         .         .  647 

547. — Pigmented  epithelium  of  the  retina,  viewed  in  transection      .         .  647 

548. — Isolated  rod  and  cone  visual  cells  of  the  pig  .         .         .         .  648 

549. — Diagram  of  the  rod  and  cone  visual  cells,  and  their  respective  bipolar 

neurons         . 649 

550. — A  rod  and  cone  visual  cell  from  the  fundus  of  the  human  retina, 

outside  the  macula  lutea          .......  650 

551. — Two  cones  from  the  human  retina       .         .         .         .         .  650 

552. — From  the  human  retina      . 651 

553. — Diagrams  of  the  human  retina,  showing  the  relationships  to  each 

other  of  the  retinal  neurons,  and  their  disposition  in  the  different 

layers 652 

554. — From  a  meridional  section  of  a  child's  eye,  showing  the  layers  of 

the  retina  at  a  point  midway  between  the  macula  lutea  and  the 

ora  serrata 653 

555. — Horizontal  cell  from  the  retina  of  a  calf        .         .  '  .         .  655 

556. — Two  amacrine  cells  from  a  transection  of  the  retina  of  a  calf  .  656 

557. — A  nerve  cell  of  the  large  ganglion  cell  layer;  from  the  retina  of  a  cat    .  657 

558. — A  fiber  cell  of  Miiller,  or  sustentacular  cell,  from  the  dog's  retina   .  658 

559. — Transection  through  the  fovea  centralis  retinae      .          .         .•         .  660 
560. — Developing  rod  and  cone  visual  cells,  from  the  retina  of  a  345  mm. 

(6  mos.)  human  fetus 661 

561. — Two  early  stages  in  the  development  of  the  rod  and  cone  visual  cells 

in  the  chick  662. 

562. — Diagram  illustrating  Balfour's  theory  to  account  for  the  inversion 

of  the  visual  cells  of  the  vertebrate  retina          ....  663 

563. — Entrance  of  the  optic  nerve 664 

564— Lens  fibers 667 

565. — The  nuclear  zone  at  the  margin  of  the  crystalline  lens  of  a  child's 

eye,  showing  the  transition  of  the  lens  epithelium  to  the  lens  fibers 

and  the  attachment  of  the  suspensory  ligament          .         .         .  668 

566. — Schematic  representation  of  the  intrinsic  blood  vessels  of  the  eye    .  671 

567. — Vertical  section  through  the  upper  eyelid 675 

568.— Arterial  supply  of  the  eyelid 678 

569. — Section  through  a  lobule  of  the  lacrimal  gland  of  man  .         .  680 

570. — Portions  of  two  adjacent  lobules  of  the  lacrimal  gland  of  the  rabbit, 

showing  two  stages  in  secretory  activity  of  the  tubules       .         .  681 

571. — Transection  of  the  lobule  of  the  external  ear  of  an  infant  .  683 


xxviii  LIST  OF  ILLUSTRATIONS 

FIGURE  PAGB 

572. — From  the  external  acoustic  meatus  of  man            ....  684 

573. — Transection  of  the  tympanic  membrane  of  a  child          .          .         .  687 

574. — Section  through  the  margin  of  the  tympanic  membrane  of  a  child  .  688 

575. — The  auditory  ossicles          .         .         .  * 689 

576. — The  cavity  of  the  tympanum,  viewed  from  above  .  .  .  690 
577.— Transection  of  the  Eustachian  tube;  diagrammatic  .  .  .692 

578.— The  bony  labyrinth 694 

579. — Diagram  of  the  membranous  labyrinth  in  lateral  view            .         .  695 

580. — Diagram  of  the  right  membranous  labyrinth         ....  696 

581. — The  isolated  membranous  labyrinth 696 

582. — Transection  of  the  margin  of  the  macula  acustica  sacculi  of  a  guinea- 
pig        697 

583.— Nerve  endings  in  the  macula  acustica  of  a  guinea-pig    .         .         .698 

584. — Transection  of  a  human  semicircular  canal            ....  700 

585. — Axial  section  through  the  cochlea  of  a  fetal  calf    ....  701 

586. — Axial  section  through  a  turn  of  the  cochlea  of  a  guinea-pig  .  .  702 
587. — A  radial  section  through  Corti's  organ  in  the  first  turn  of  the  human 

cochlea 707 

588. — Diagram  of  the  organ  of  Corti    .         .         .         .         .         .         .711 

589. — Axial  section  through  Corti's  organ  of  the  guinea-pig,  showing  the 

terminal  nerve  fibrils      ........  713 

590. — Scheme  of  the  vascular  supply  of  the  internal  ear  .  .  .714 
591. — Scheme  of  the  vascular  terminations  in  the  wall  of  the  cochlear 

canals 715 

592. — Semidiagrammatic  illustrations  of  successive  stages  in  the  develop- 
ment of  the  internal  ear  of  the  chick 718 

593. — Wax  reconstructions  of  three  early  stages  in  the  development  of  the 

internal  ear  (membranous  labyrinth)  of  man     ....  718 

594. — A  method  of  preparing  a  paper  box  for  paraffin  embedding    .         .  737 

PLATES 

A. — Successive  stages  in  the  spermatogenesis  of  Schistocerca  damnifica  .  465 
B. — Successive  stages  in  the  spermatogenesis  of  Schistocerca  damnifica 

(continued) 467 

C. — Successive  stages  in  the  spermatogenesis  of  Schistocerca  damnifica 

(continued) 469 

D. — Successive  stages  in  the  growth,  maturation,  and  fertilization  of  the 

egg  of  the  starfish,  Asterias  forbesii 471 


A    TEXT-BOOK    OF 
HISTOLOGY 


A  TEXT-BOOK  OF  HISTOLOGY 

CHAPTER   I 

INTRODUCTION— PROTOPLASM— CELL 
INTRODUCTION 

Definition  of  Histology. — Histology  is  the  science  of  tissue  struc- 
ture, plant  or  animal.     It  concerns  itself,  therefore,  chiefly  with  the 
structural  characteristics  and  interrelationships  of  the  component  ele- 
ments of  tissues.     These  elements  are  the  cells,  and  the  material  con- 
necting or  separating  the  cells,  the  intercellular  substances.     A  tissue 
consists  of  cells  associated  in  the  performance  of 
a  specific  function.     A  cell  may  be  defined  in  a 
preliminary  way  as  the  unit  of  organic  structure 
and  function.     The  minuter  details  of  histology 
involve  also  cell  anatomy  or  cytology.     Here  we 
meet  with  the  essential  substance  of  the  cells,  the 
protoplasm,  or  bioplasm,  the  'material  basis  of  life/ 
We  also  meet  with  the  chief  'organ*  of  cells,  the 
nucleus.     A   completer   definition   of   a   cell   may 
accordingly  be  given  as  a  circumscribed  mass  of 
protoplasm  containing  a  nucleus  (Fig.  1).    A  com-       FIG.  1.— VARIOUS 
plete    histologic    description    embraces,    therefore,     SPHEROIDAL  CELLS, 

details  of  the  relationships  of  the  component  cells     -1'  ov™%  fr°m  ovary 
,      ,   ,,  ,         .  ,   of  a  child;   2,  sperm- 

of  a  tissue,  and  of  the  protoplasmic  structure  and  atocyte;  and  3,  sperm- 
nuclear    characteristics    of    the    types    of    cells    in-  atid,  from  the  testicle 

volved.      Histology   includes   further   the    data    of  °f.  a  ra|?bit-   .Hema- 

T  .  ,  .  ,    tern    and    cosin.      X 

tissue  origin  and  development,  or  histogenesis,  and   759. 

of  cell  origin  and  development,  or  cytogenesis. 
Cells  are  the  'building  stones'  of  tissues;  tissues  combine  to  form  organs; 
organs  are  associated  into  systems.  Histology  is  accordingly  a  part  of 
general  anatomy;  it  is  tissue  anatomy;  that  part  of  histology  which  con- 
siders the  relationships  between  tissues  in  organs  is  sometimes  spoken  of 
as  microscopic  anatomy. 

2  1 


£  INTRODUCTION— PROTOPLASM— CELL 

Historical  Development  of  Histology.— Modern  human  histology 
had  its  origin  in  the  work  of  Bichat  (1771-1801).  He  did  not  employ 
the  microscope;  but  his  careful  and  extensive  studies  of  the  minute 
anatomy  of  tissues  gave  the  impulse  and  general  outline  for  later  studies 
by  means  of  the  microscope  through  which  mammalian  histology  has 
grown  to  a  relatively  complete  science.  Great  impetus  was  given  also  by 
the  announcement  of  the  'cell  theory'  by  Schleiden  and  Schwann  in  1839, 
namely,  the  statement  that  all  tissues  are  composed  of  structural  units, 
or  cells.  Other  epochal  steps  in  histologic  science  were  the  recognition  of 
the  nucleus  by  Eobert  Brown  in  1831,  and  of  protoplasm  by  v.  Mohl 
in  1846.  Cytology  arose  almost  as  an  incident  to  embryology.  It  traces 
its  origin  to  the  work  of  0.  Hertwig  on  the  fertilization  of  the  sea 
urchin's  egg  (1875).  It  is  the  infant  anatomic  science,  its  late  develop- 
ment being  due,  largely,  to  its  dependence  upon  the  optical  and  me- 
chanical refinements  of  the  microscope.  It  deals  with  fundamental 
structures  within  the  limits  of  visibility,  and  is  destined  to  grow  to  vast 
proportions,  as  the  already  voluminous  literature  on  'mitochondria' 
('plastosomes')  in  part  foreshadows. 

Relation  of  Histology  to  Other  Biologic  Sciences. — Histology 
aims  to  complete  anatomic  knowledge.  It  is  thus  the  complement  of 
gross  anatomy..  It  furnishes  also  essential  preliminary  data  for  the 
understanding  of  pathology;  abnormal  structure  and  function  become 
fully  intelligible  only  in  the  light  of  normal  histology.  It  is  funda- 
mental also  to  physiology,  the  science  of  normal  function. 

A  certain  function  demands  a  specific  structure;  structure  and  func- 
tion sustain  reciprocal  relationships.  Xormal  function  depends  upon 
the  normal  structure  of  the  cells  involved  in  the  function ;  abnormal 
function,  or  disease,  is  associated  with  altered  cellular  structure.  His- 
tology gains  enormously  in  interest  and  value  to  the  student  who  will 
always  keep  well  in  mind  the  function  that  a  Certain  structure  under 
consideration  is  called  upon  to  perform.  Embryology  also  to  a  consid- 
erable extent  builds  upon  histologic  and  cytologic  data. 


PROTOPLASM 

Chemical  Constitution.— The  unit  of  both  structure  and  function 
is  the  cell.  The  essential  constituent  of  cells  is  protoplasm.  Protoplasm 
may  be  thought  of  as  a  physicochemical  mechanism.  Chemically,  it  is  a 
very  complex  aqueous  mixture  of  substances,  containing  the  elements, 


PEOTOPLASM  3 

carbon,  oxygen,  hydrogen,  nitrogen,  and  small  quantities  of  sulphur, 
phosphorus,  calcium,  sodium,  chlorin,  magnesium,  potassium  and  iron. 
The  principal  compounds  of  protoplasm  are  proteins,  which  furnish 
the  main  source  of  energy  expended  in  function;  carbohydrates;  fats; 
and  water,  which  constitutes  about  three-quarters  of  its  weight.  It  is 
believed  by  one  school  of  biologists  (mechanists)  that  if  we  had  the 


f&&?. '{&£& 

p 


/ 

"  I       wf^%jjj&^ 

J* 


c.tf 


FIG.  2. — AMEBA  PROTEUS  IN  MOTION. 

c.v.,  contractile  vacuole;/.^.,  food  vacuole;  n.,  nucleus;  w.v.,  water  vacuoles.  The 
arrows  indicate  the  direction  of  the  protoplasmic  flow.  Note  the  peripheral  non- 
granular  ectoplasm,  and  the  granular  endoplasm.  (From  Calkins'  "Biology," 
H.  Holt  &  Co.,  after  Sedgwick  and  Wilson.) 


formula  for  the  proper  stereo-isomeric  association  of  the  elements  and 
compounds  of  protoplasm,  life  could  be  artificially  produced;  another 
school  of  biologists  (vitalists)  assume  an  additional  'vital  principle'  as 
a  prerequisite  for  life. 

Physical  Constitution.— Physically,  protoplasm  is  a  granular  semi- 
fluid or  gelatinous  substance.  It  possesses  properties  characteristic  of 
both  solids  and  liquids.  It  is  an  aggregate  of  colloids  and  crystalloids. 
The  physicochemical  laws  which  govern  the  crystalloids  and  colloids 
underlie  the  properties  of  living  matter.  An  organism  is  essentially 


INTEODUCTIOX— PROTOPLASM— CELL 


TtflCHOCYSTS 


5"  CANALS 


an  aqueous  solution,  holding  in  suspension  colloidal  substances  of  great 
complexity.     Crystalloids  are  divisible  into  two  groups :  electrolytes  and 

non-electrolytes.  The  one  (salts, 
acids,  bases)  in  solution  conduct 
the  electric  current,  the  others 
(urea,  sugar)  do  not.  Colloids  ex- 
ist in  two  states,  a  liquid  or  sol 
state,  and  a  semi-solid  or  gel  state. 
There  exists  no  sharp  line  of  di- 
vision between  colloids  and  crystal- 
loids ;  these  terms  designate  phases 
or  states  rather  than  substances; 
between  them  lie  all  kinds  of  inter- 
mediate grades.  Protoplasm  is  a 
sol ;  and  since  its  fluidity  is  due  to 
water,  it  is  commonly  classed  as  a 
liydrosol.  It  passes  readily  into  a 
gel  condition,  thus  becoming  a  liy- 
drogel.  In  living  protoplasm  this 
-metamorphosis  is  a  reversible  proc- 
ess. Agents  which  effect  an  irre- 
versible gelation  of  protoplasm 
tend  to  bring  life  to  a  standstill. 
Fixation,  or  killing,  of  tissue  for 
microscopic  study  consists  in  a  sep- 
aration of  the  more  solid  part  of 
colloidal  protoplasm  from  a  more 
liquid  part.  Death  is  histologically 
such  a  process  of  coagulation.  Liv- 
ing protoplasm  may  be  studied  to 
good  advantage  in  the  one-cell  ani- 
mal forms,  Ameba  (Fig.  2)  or 
Paramecium  (Fig.  3).  These  and 
other  equally  favorable  protozoan 
forms  are  readily  available  from  hay  infusion  cultures,  and  can  be  profit- 
ably employed  for  the  demonstration  also  of  the  simpler  modes  of  proto- 
plasmic activity,  and  of  the  changes  suffered  by  protoplasm  in  passing 
from  the  living  to  the  dead  condition.  Since  protoplasm  is  commonly 
organized  into  cells,  the  next  step  demands  a  knowledge  of  a  typical  or 
generalized  cell. 


CONTRACTILE  V, 


FIG.  3. — PARAMECIUM  CAUDATUM. 

Note  the  peripheral  cilia  and  the  gran- 
ulo-alveolar  character  of  the  protoplasm. 
(From  Calkins'  "Biology,"  H.  Holt 
&Co.) 


THE  CELL 


THE    CELL 

General  Statements. — A  generalized  cell  is  of  spheroidal  shape  (un- 
modified by  pressure)  and  contains  certain  'organs'  and  a  variety  of  fun- 
damental and  secondary  elements  (Fig.  4).  A  cell  (or  protoplast; 
Hanstein)  is  a  mass  of  protoplasm  endowed  with  vital  properties.  The 
confines  of  such  a  cellular  mass  of  protoplasm  exist  in  a  cell  membrane. 


FIG.  4. — -A  GENERALIZED  CELL. 

o,  exoplasm;  b,  endoplasm;  c,  spongioplasm;  d,  hyaloplasm;  e,  microsomes;  /, 
chromidia;  g,  centrosome  (centriole);  h,  centrosphere,  surrounded  by  astrosphere;  i,  cell 
membrane ;j,  deutoplasmic  granule;  k,  fluid  vacuole,  or  oil  drop;  I,  mitochondria  or 
plastosomes;  m,  nuclear  membrane;  n,  nucleolus;  o,  linin;  p,  karyosome;  q,  chromatin 
(net  knot);  r,  foreign  inclusions,  pigment,  etc.  (metaplasm). 

This  represents  a  differentiation  product  of  protoplasm;  when  robust 
as  in  plant  cells,  it  forms  a  cell  wall.  In  certain  cells,  e.g.,  white  blood- 
cells,  it  is  apparently  lacking;  however,  in  these  so-called  naked  cells  the 
peripheral  layer  of  protoplasm  is  more  condensed  and  most  probably 
subserves  the  osmotic  function  of  a  distinct  membrane.  In  fact,  the 
surfaces  of  protoplasm  possess  the  properties  of  semipermeable  mem- 
branes, probably  lipoid  in  nature.  An  essential  organ  of  the  cell  is  the 
nucleus.  It  is  trophic  in  function,  the  center  of  oxidation  processes. 
In  certain  protozoa  this  is  represented  by  scattered  nuclear  materials 


INTRODUCTION— PROTOPLASM— CELL 


or  granules  (Fig.  5).  The  shape  of  the  nucleus  is  spherical;  typically 
it  has  a  central  location,  but  it  frequently  assumes  eccentric  positions. 
It  is  physically  denser  and  more  elastic  than  the  extranuclear  protoplasm. 
Its  periphery  simulates,  or  perhaps  consists  of,  a  membrane,  the  nuclear 
wall.  Whether  as  a  membrane  it  be  complete  or  reticulated,  whether  of 
nuclear,  cytoplasmic  or  composite  origin,  are  undecided  points.  Eecent 
investigations  on  the  nuclear  membrane  indicate 
that  it  is  fenestrated;  such  conditions  would  per- 
mit of  an  easy  escape  of  nuclear  material  into  the 
cytoplasm. 

Nucleus. — The  protoplasm  composing  the  nu- 
cleus is  known  as  nudeoplasm  or  Jcaryoplasm; 
that  constituting  the  remainder  of  the  cell,  the 
cytoplasm.  The  nuclear  constituents  include  a  more 
fluid  ground  substance  or  nuclear  sap  (karyo- 
lymph:  paralinin),  throughout  which  extends  a 
delicate  reticulum  of  linin'  threads  (Fig.  4). 
Upon  these  linin  or  achromatin  threads  are  sup- 
ported, more  abundantly  at  the  points  of  inter- 
section of  the  mesh,  granules  (chromioles)  and 
masses  (net-knots)  of  a  substance  staining  deeply 
in  the  basic  dyes,  the  chromatin.  Spheroidal  net- 
knots  are  known  as  Jcaryosomes.  The  linin  is 
said  to  be  achromatic.  Whether  it  is  chemically 
different  from  chromatin  or  simply  more  atten- 
uated chromatin  is  disputed.  The  'chromatic'  gran- 
ules themselves  undergo  changes  in  stainability : 
on  the  basis  of  reaction  to  acid  and  basic  dyes, 
this  substance  is  divided  into  oxy chromatin  (Jan- 
tanin)  and  basichromatin.  Linin  and  chromatin 
are  regarded  by  some  as  different  phases  in  the 
elaboration  of  the  same  substance.  The  nucleus  in- 
cludes, furthermore,  usually  one,  frequently  more, 
nucleoli.  These  do  not  grade  into  the  nuclear  sap,  like  the  nuclear 
network,  but  are  limited  by  a  sharp  line  of  demarcation.  They  may  be 
achromatic,  when  they  are  known  as  plasmosomes,  or  they  may  take  on 
chromatin,  becoming  chromatin  nucleoli.  It  is  uncertain  whether  the  lat- 
ter are  identical  in  all  cases  with  the  karyosomes.  The  difference  among 
nucleoli  is  more  probably  one  of  degree  of  abundance  of  chromatin.  The 
nucleus  is  the  metabolic  organ  of  the  cell ;  without  a  nucleus  a  cell  may 


FIG.  5.— A  UNI- 
CELLULAR FLAG- 
ELLATE ANIMAL 
(TETRAMITUS 

CHILOMONAS). 

Showing  the  nu- 
clear material  dis- 
tributed as  granules 
throughout  the  cell. 
(Redrawn  from 
Calkins.) 


THE  CELL 


continue  to  live  for  a  time,  but  it  can  neither  grow  nor  undergo  progres- 
sive differentiation.  All  changes  in  enucleated  protoplasm  are  regressive, 
leading  to  death.  The  nucleus  is  also  largely  the  reproductive  center,  as 
will  be  described  below.  The  nucleolus  plays  the  role,  among  other  pos- 
sible functions,  of  a  center  of  storage,  perhaps  also  elaboration,  of  chro- 
matin.  Xuclear  protoplasm,  more  especially  the  chromatin,  is  relatively 
rich  in  phosphorus. 

Astral  System. — Another  organ  of  a  typical  cell  is  the  aster,  astral 
system  or  attraction  sphere.  Its  substance  is  collectively  known  as  archo- 
plasm.  It  usually  lies  outside  of, 
but  close  to,  the  nucleus;  in  cer- 
tain cells  it  is  intranuclear,  e.g., 
spermatocytes  of  Ascaris.  It  con- 
sists centrally  of  a  granule,  the 
centrosome;  in  this,  in  certain  in- 
stances, may  be  differentiated  cen- 
trally a  smaller  granule,  the  cen- 
triole;  when  the  latter  appears, 
the  more  outlying  portion  of  the 
centrosome  is  designated  the  cen- 
troplasm.  The  centrosome  may 
divide  into  two,  becoming  a  diplo- 
some,  or  in  some  instances  it 
may  become  multiple,  when  it  is 


FIG.    6. — EGG    OF    A    CLAM    (CUMINGIA 

TELLINOIDES). 

Showing  the  first  maturation  spindle 
with  centrosomes  and  chromosomes  at 
metaphase,  and  the  disappearing  nucleojus 
(ri)  at  the  right.  X  1000. 


known  as  a  pluricorpuscular  cen- 
trosome. Surrounding  the  cen- 
trosome is  a  clearer,  minutely 
granular  sphere,  the  centrosphere ; 
radiating  from  this  peripherally  are  delicate  astral  rays,  collectively 
known  as  the  astrosphere  (Fig.  6).  Structurally  the  aster  is  subject  to 
considerable  variations  in  different  cells.  On  account  of  its  relation  to 
cell  division,  it  is  regarded  as  the  dynamic  center  of  the  cell ;  viewed  thus 
its  substance  is  known  as  Jcinoplasm.  The  attraction  sphere  may  or  may 
not  be  visibly  present ;  in  all  living  cells  it,  or  its  analogue,  is  generally 
believed  to  be  potentially  present. 

Cytoplasm. — The  cytoplasm  may  be  divided  into  a  thin  peripheral  or 
cortical  layer  of  less  granular  protoplasm,  the  exoplasm  (ectoplasm), 
and  the  main  central  mass,  the  endoplasm.  In  certain  highly  differen- 
tiated cells  the  exoplasm  is  not  discernible.  In  others,  at  certain  stages 
m  the  development  it  contains  the  products  of  differentiations,  when  it  is 


INTRODUCTION— PROTOPLASM— CELL 


FlG.     7. — P  R  I  M  A  R  Y 

SPERMATOCTTE  OF 
A  TURTLE  (CiSTUDO 
CAROLINA). 


known  as  'deuteroplasm'  (Studnicka).  The  endoplasm  is  commonly 
described  as  consisting  of  a  more  fluid,  finely  granular  ground  substance. 
the  hyaloplasm  (paraplasm,  interfilar  mass,  para- 
mitome,  enchylema,  cytolymph),  containing  a  del- 
icate denser  reticulum,  or  cytoreticulum,  with 
polygonal  or  spheroidal  meshes.  The  substance  of 
the  reticulum  is  called  spongioplasm  (mitome; 
filar  mass).  It  is  held  by  some  to  be  continuous 
with  the  linin  mesh  of  the  nucleus.  The  granules 
of  the  ground  substance,  both  free  of  and  attached 
to  the  spongioplasm,  are  called  microsomes.  Ac- 
cording to  one  interpretation  the  spongioplasm 
arises  by  coalescence  of  microsomes.  A  more  re- 
Showing  chromatic  cent  interpretation  regards  both  network  and 
spherules  ('chromidia')  granule  as  simply  more  condensed  portions  of  the 

apparently  in  process     hyaloplasm.     The  cytoplasm  may  contain,  besides 
of  extrusion  from  the      ,/  _ J.  J    * 

nucleus.    X  1500.  the  aforementioned  fundamental  constituents,  nu- 

tritive materials  including  yolk  granules  or  glo- 
bules (deutoplasm) ;  vacuoles,  foreign  enclosures,  e.g.,  bacteria,  etc.,  and 
pigment  (metaplasm)  ;  plastids  (in  plant  cells)  ; 
chromidia  (Fig.  7),  masses  of  chromatic  gran- 
ules, presumably  of  nuclear  origin,  and  probably 
the  raw  material  for  certain  differentiation  prod- 
ucts ;  and  mitochondria  or  plastosomes. 

Mitochondria. — Mitochondria  are  cytoplas- 
mic  elements  of  very  variable  form  and  of  almost 
universal  distribution.  These  are  destined  to 
bulk  very  large  in  immediate  cytological  investi- 
gations. They  may  prove  to  be  very  important 
elements  of  the  more  fundamental  protoplasmic- 
structure  and  function.  In  the  germ  cells  of 
vertebrates,  as  in  undifferentiated  cells  generally, 
they  are  for  the  most  part,  granular  (chondrio- 
somes)  (Fig.  8)  ;  in  the  somatic  differentiated 
cells  filamentous  or  rod-shaped  (chondriomites; 
chondrioconts;  pseudochromosomes)  (Figs.  9 
and  10).  Both  chromidia  and  trophospongium  £^pfasmic  Sphere> 
(a  canalicular  network  of  the  cytoplasm,  prob- 
ably concerned  with  circulation  of  nutritive  material  or  secretion  prod- 
ucts) (Fig.  11)  have  been  identified  with  mitochondria.  Trophospon- 


FIG.  8. — SPERM ATID  OF 
OPOSSUM  IN  EARLY 
STAGE  OF  METAMOR- 
PHOSIS INTO  A  SPER- 

MIUM. 

Showing  granular 
mitochondria,  m,  in  the 
cytoplasm,  n,  nucleus, 


THE  CELL 


gium  at  least  is  a  distinct  structure,  and  chromidia  more  probably  also, 
though  by  some  regarded  as  tbe  elements  from  which  the  filamentous 
mitochondria  are  formed.  M  itorhondria  have  been  credited  with  most 


a  b  c  ,1 

FIG.  9.  —  CELLS  FROM  THE  NEWLY  HATCHED  RAINBOW  TROUT,  TREATED  ACCORDING 
TO  MEVES'  TECHNIC  FOR  THE  DEMONSTRATION  OF'MITOCHONDRIA  (PLASTOSOMES). 
a  and  b,  cartilage  cells;  c,  young  blood  cell;  d,  epithelial  cells  from  the  intestine. 
X  2000. 

various  functions,  e.g.,  formation  of  presecretion  and  excretion  granules, 
and  the  formation  of  various  kinds  of  fibrils.  M.  ITeidenhain  regards  the 
chondriosomes  as  vegetative  organs  of  the  cells  subserving  metabolism. 


\ 

FJG.  10. — Two  CELLS  FROM  THE  MESENCHYMA  OF  THE  NEWLY  HATCHED  RAINBOW 

TROUT. 

The  one  to  the  left  (a)  at  late  anaphase  of  mitosis,  showing  mitochondria  (plasto- 
somes).     Meves'  technic.     X  2000. 

Our  knowledge  is  as  yet  too  limited  to  speak  with  assurance  either  as  to 
their  origin,  complete  function,  or  fate.  One  thing  only  is  certain, 
namely,  that  they  are  actual  constituents  of  the  cytoplasm  of  practically 


10  INTRODUCTION— PEOTOPLASM— CELL 

every  type  of  cells,  at  certain,  perhaps  all,  stages  of  development  and 
active  function.     They  have  been  seen  and  studied  even  in  living  plant 
cells    (Maximow),    and    in   animal    cells   grown    in 
artificial  media  they  wer.e  observed  by  M.  E.  and 
W.    H.   Lewis    (Amer.    Jour.    Anat,    17,   3,    1915) 
to  move,  to  change  shape,  to  divide  into  granules 
and   again   to  reunite   into   filaments — facts   which 
render    inadmissible    their    interpretation    in    fixed 
material  as  lipoid  precipitation  products    (Faurier- 
Fremier),  and  strongly  suggest  their  connection  with 
FIG     11  — INTRA-  metabolic  activity.    They  have  the  chemical  composi- 
CELLTTLAR     NET-  tion  of  a  lipoid  (probably  a  phosphatid)  united  to  an 
WORK,  OR  'TROPH-  albuminoid  base.    It  has  been  suggested  that  they  are 
IN  A  PUR'KINJE  a  suPP°rt  to,  and  the  region  of,  oxidation.     Certain 
CELL  OF  THE  CERE-  investigators  (Benda,  Meves,  Duesberg)  regard  them 
BELLUM  OF  STRix  as  ^e  cvtoplasmic  basis  of  heredity,  and  ascribe  to 

Golgi's  stain    (After  ^em  an  imPortant  T^e  in  histogenesis. 

Golgi.)  Schreiner's  findings  in  developing  fat  cells  sug- 

gest a  nutritive  significance  (vide,  p.  64). 

STRUCTURE    OF   PROTOPLASM 

Four  main  types  of  protoplasmic  structure  are  generally  recognized: 
(1)  the  homogeneous;  (2)  the  granular;  (3)  the  alveolar  or  foam  type; 
and  (4)  the  fibrillar,  (a)  reticular  or  sponge  type  and  (b)  filar  (Fig. 
12).  The  type  of  protoplasm  of  a  particular  cell  may  vary  with  the 
stage  of  development  and  function.  In  successive  stages  of  development 
and  differentiation  the  protoplasm  of  the  same  cell  may  pass  from  the 
apparently  homogeneous,  through  the  granular  and  granulo-alveolar,  to 
a  granulofibrillar  type.  Homogeneous  protoplasm,  as  for  example  the 
ectoplasmic  layer  of  ameba,  is  more  probably  to  be  interpreted  as  com- 
posed of  minute,  perhaps  ultramicroscopic,  colloidal  granules  ('colloidal 
biogens').  Young  and  undifferentiated  cells  commonly  have  a  granular 
cytoplasm.  In  general  it  may  be  said  that  the  actual  fundamental  type 
of  protoplasm  is  the  granular.  This  changes  into  the  alveolar  type  by 
the  appearance  of  spherules  among  the  granules.  The  contents  of  the 
alveoli  constitute  the  alveolar  substance;  the  inter-alveolar  sap,  the  hya- 
loplasm; the  granules,  the  microsomes;  and  the  walls  of  the  alveoli  may 
be  identified  with  the  spongioplasm  of  the  reticular  type  of  protoplasm. 
Another  interpretation  of  alveolar  protoplasm  regards  the  content  of  the 


FIG.  12. — DIAGRAM  ILLUSTRATING  THEORIES  OF  PROTOPLASMIC  STRUCTURE. 

1,  alveolar  structure;  granules  occur  only  at  the  angles  formed  by  the  alveoli.  2, 
filar  structure,  showing  filar  and  interfilar  substance.  The  centrosome  (a  diplosome) 
is  represented  in  this  portion;  it  is  surrounded  by  a  clear  attraction  sphere.  3, 
granular  structure;  coarse  microsomes  irregularly  disposed.  This  portion  contains 
three  foreign  bodies  which  have  been  included  by  the  cell,  a  streptococcus,  a  crys- 
tal, and  a  spheroidal  pigment  mass.  4>  the  alveolar  walls  are  formed  by  regularly 
arranged  microsomes;  a  vacuole  is  shown  in  this  section.  5,  reticular  structure. 

The  cell  is  inclosed  by  a  cell  membrane,  and  contains  a  central  nucleus  in  which  are 
shown  the  nuclear  membrane,  indistinct  linin  fibrils,  deeply  stained  chromatin  in 
coarse  threads  and  irregular  masses  (karyosomes),  and  a  centrally  situated  nucleolus 
or  plasmosome. 


.••>;  Vv., 
|S»|t5*w  II'    !*•••••••••'  •'•  *«V 

iillMf  l|p 

-••'?SX 


FIG.  13. — EGG   OF  THE  BLOOD  STARFISH  IN  LATER  GROWTH  PERIOD. 
Showing  a  stage  in  the  change  of  an  earlier  granular  to  a  later  alveolar  condition 
of  the  cytoplasm.     The  nucleus  contains  many  spherical  nucleoli  of  various  sizes. 
The  space  (a)  is  a  fixation  artifact.     X  1500. 

11 


12 


INTRODUCTION— PEOTOPLASM— CELL 


_'<•* 


alveoli  as  hyaloplasm.  The  microsomes  may  in  part  be  closely  associated 
with  the  alveolar  walls,  perhaps  forming  them  and  the  spongioplasm  by 
the  process  of  coalescence.  The  so-called  alveolar 
protoplasm  is  in  reality  of  the  granulo-alveolar  type, 
The  spherules  probably  arise,  at  least  in  part,  by  a 
process  of  liquefaction  of  some  of  the  granules.  The 
alveologranular  is  probably  the  commonest  type  ot 
protoplasm.  The  process  of  transformation  of  the 
granular  into  the  alveolar  type  can  best  be  demon- 
strated in  young  growing  eggs  of  invertebrates.  Fig. 
13  shows  an  egg  in  which  the  perinuclear  protoplasm 
is  predominantly  alveolar,  the  more  peripheral  por- 
tion granular.  The  metamorphosis  is  apparently 
under  the  control  of  the  nucleus. 

Other  commonly  described  types  of  protoplasmic 
structure  may  be  interpreted  in  terms  of  mechanical 
(extraneous;  artificial)  alterations  in  the  alveolar  type.    Thus  a  rctimlur 
type  may  be  derived  from  the  alveolar  through  modification  (by  pressure, 


FIG.  14. — PANCREAS 
CELL  OF  TURTLE, 
FILLED  WITH  ZY- 
MOGENIC  GRAN- 
ULES. 

n,   nucleus,  with 
nucleolus.    X  2000. 


FIG.  15. — MOTOR  NERVE  CELL  FROM  THE  VENTRAL  HORN  OF  THE  SPINAL   CORD 

OF  THE  Ox. 

Showing  Nissl  granules  in  the  cell  body  and  its  dendritic  processes.  The  non- 
granular  process  at  the  left  is  the  axon.  p,  pigment.  (From  Barker's  "The  Nervous 
System,"  after  von  Lenhossek.) 


STRUCTURE  OF  PROTOPLASM 


or  distortion)  of  the  spherical  alveoli  into  polyhedral  or  irregular  com- 
partments. Likewise  the  fibrillar  or  filar  types  may  be  interpreted  as 
similar  more  extensive  modifications  resulting  in  ruptures  of  the  alveoli 
and  consequent  finer  or  coarser  indiscriminate  aggregations  of  spongio- 


/ 


// 


FIG.  16. — INTERSTITIAL  CELL,  FROM  THE 
TESTIS  OF  A  TWENTY-ONE  YEAH  OLD 
MAN,  SHOWING  GRANULAR  AND  FILA- 
MENTOUS MITOCHONDRIA. 
After  Winiwarter. 


FIG.  17. — A  NEURON  (GIANT  PYRAMIDAL 
CELL,  OR  CELL  OF  BETZ)  FROM  THE 
CEREBRAL  CORTEX  OF  MAN,  SHOW- 
ING THE  NEUROFIBRILS. 

Bielschowsky  technic.     X  500. 


plasmic  fibrils,  or  as  the  result  of  the  coalescence  of  granules  to  form 
fibrils.  The  distinction  between  fundamentally  granular  and  alveolar 
protoplasm,  and  secondarily  derived  types  of  granular  and  reticular 
(fibrillar)  protoplasm  must  be  emphasized.  In  the  performance  of  spe- 
cific functions,  certain  cells  elaborate  secretory  gran- 
ules (gland  cells,  Fig.  14;  nerve  cells,  Fig.  15;  cells 
with  crystalloids,  Fig.  16) ;  others  produce  various 
types  of  fibrils  (e.g.,  nerve  cell,  Fig.  17;  connective 
tissue  cells,  and  muscle  cells)  ;  others  elaborate  fat 
spherules  (e.g.,  Fig.  18) ;  and  still  others  a  canalicu- 
lar  (trophospongium)  apparatus  (Fig.  19). 


FIG.  18.— DEVEL- 
OPING FAT  CELLS. 
The  fat  droplets, 
after  extraction 
with  alcohol  and 
ether,  appearing  as 
vacuoles.  Hematein 
and  eosin.  X  550. 


The  foregoing  description  of  protoplasmic  struc- 
ture pertains  largely  to  the  'fixed'  (dead)  condition.  In 
this  connection  the  terminology  employed  will  continue 
useful.  But  recent  more  refined  physiochemical  studies 
of  living  protoplasm  have  aroused  considerable  skepti- 
cism respecting  the  verity  of  actual  specific  structures  corresponding  to  the 
designations  applied,  more  especially  the  spongioplasmic  and  limn  network. 
Perhaps  the  most  that  can  be  said  with  certainty  regarding  the  fundamental 
structure  of  protoplasm  is  to  describe  it  as  a  'granular  gel.'  Kite's  studies 


14  INTRODUCTION— PROTOPLASM— CELL 

tAmer.  Jour.  Phys.,  32,  2,  1913)  of  the  physical  properties  and  molar  struc- 
ture of  protoplasm  in  various  cells,  by  combined  methods  of  microdissection 
and  vital  staining,  have  led  to  clearer  conceptions  in  this  field.     Kite  ac- 
cepts the  interpretation  of  protoplasm  as  an  emulsoid,  the  real  structural 
units  of  which  are  the  colloidal  particles;  and  he  con- 
ceives of  the  optiejil  imatre  ;is  the  result  of  the  com- 
bination of  the  physical  phenomena  of  reflection,  re- 
fraction, diffraction,  absorption,  dispersion,  interfer- 
>f\  ence,  and  a  scattering  action  on  light.     Living  proto- 

plasm   is    an    apparently    homogeneous    and    viscous 
IPP^IMHyM         hydrogel,  holding  in  suspension  in  the  form  of  gran- 
ules ('microsomes')  minute  masses  of  denser  gels,  and 
liquid  globules   ('alveoli')   which  show  many  of  the 

optical  properties  of  an  oil  drop.     The  'network'  and 
FIG.  19. — COLUMNAR  i        v  a.-     i     • 

CILIATED  EPITHE-       granules'  of  the  nucleus  Kite  regards  as  optical  phe- 

LIAL  CELLS,  SHOW-  nomena,  areas  of  greater  concentration  in  the  nuclear 
ING  CANALICULAR  gel,  not  separated  from,  but  grading  into  the  sur- 
APPARATUS.  rounding  diluter  gel  of  the  'nuclear  sap.'  Spindle 

After  Holmgren.          fibers  were  successfully  dissected  out  of  the  proto- 
plasm as  distinct,  relatively  rigid  threads.    These  com 

elusions  are  in  the  main  in  accord  with  those  deduced  from  the  earlier 
physiochemical  studies  of  protoplasm  and  colloids  by  Hardy  and  others. 
M.  R.  and  W.  H.  Lewis  (op.  cit.)  also  find  no  sign  of  a  reticular  or  of  an 
alveolar  structure  in  either  cytoplasm  or  nucleus  in  cells  studied  in  tissue 
cultures.  They  describe  both  cytoplasm  and  nucleus  as  'finely  granular 
almost  homogeneous  in  appearance.' 


VITAL   PROPERTIES    OF    CELLS 

Living  protoplasm  is  capable  of  certain  specific  reactions  (physiologi- 
cal processes)  or  functions.  These  reactions  are  spoken  of  as  vital  prop- 
erties or  attributes  of  protoplasm.  They  are  general  properties  of  living 
matter.  They  include  primarily  (1)  metabolism;  (2)  irritability;  (3) 
contractility;  (4)  reproduction. 

(1)  Metabolism. — Metabolism  is  that  property  of  living  proto- 
plasm by  virtue  of  which  it  can  elaborate  from  raw  food  material  the 
complex  chemical  compounds  of  protoplasm  (anabolic  phase,  construc- 
tive metabolism,  assimilation),  and  convert  the  same  into  kinetic  energy 
for  the  performance  of  specific  functions  (katabolic  phase,  destructive 
metabolism,  dissimilation),  e.g.,  secretion  and  excretion.  Metabolism 
generally  involves  growth  and  differentiation.  Development  also  is 


VITAL  PROPERTIES  OF  CELLS  15 

fundamentally  a  metabolic  process,  and  in  essence  consists  of  'a,  progres- 
sive differentiation  of  complex  and  specialized  structures  and  functions 
from  relatively  simple  and  generalized  beginnings'  (Conklin). 

(2)  Irritability. — Irritability,  or  sensitivity,  is  a  fundamental  or 
general  property  of  protoplasm.  It  is  characterized  by  a  capacity  to 
receive  and  make  response  to  stimuli,  by  changes  of  vital  processes.  Its 
prerequisite  is  the  protoplasmic  property  of  conductivity,  and  its  expres- 
sion in  many  instances  depends  upon  the  property  of  contractility.  In 
a  comprehensive  sense,  stimulus  is  every  alteration  in  the  external  vital 
condition  (Verworn).  The  reaction  to  stimuli  may  exhibit  itself  in 
one  of  three  modes:  functional,  nutritive,  and  formative  (Verworn). 


FIG.  20. — SUCCESSIVE  STAGES  IN  THE  MOVEMENT  OP  AN  AMEBA. 
The  cells  contain  a  nucleus,  a  contractile  vacuole  and  protoplasmic  granules. 
(After  Verworn.) 

Stimuli  are  of  various  sorts,  e.g.,  thermal,  mechanical,  chemical,  photic, 
solar,  galvanic  (or  electric),  fluid,  current,  gravity.  The  simplest  re- 
sulting reactions,  expressed  in  unicellular  forms  in  terms  of  orientation 
(tropism)  or  contact  (taxis) — represented  by  automatic  responses  or 
reflexes  in  higher  forms — are  respectively  thermotropism,  stereotropism 
(barotaxis;  thigmotaxis),  chemotropism,  phototropism,  heliotropism, 
galvanotropism,  hydrotropism,  rheotropism,^  and  geotropism.  Response 
may  be  either  toward  or  away  from  the  source  of  stimulus.  In  the  case 
of  the  electric  current  or  water  currents,  for  example,  simple  organisms 
may  orient  themselves,,  or  protoplasm  may  move,  in  line  with  or  opposite 
to  the  current;  these  opposite  reactions  are  called  positive  and  negative 
tropisms  respectively.  Responses  involve  fundamentally  metabolic 
changes. 

(3)  Contractility. — Motion  results  from  response  to  certain  stim- 
uli, that  is,  by  reason  of  irritability;  and  it  is  dependent  upon  the  vital 
phenomenon  of  contractility.  Motion  is  of  various  types,  predominant 
among  which  are  (a)  ameboid,  (b)  ciliary,  (c)  molecular,  (d)  circula- 
tory (streaming;  protoplasmic),  and  (e)  muscular. 


INTRODUCTIOX— PROTOPLASM— CELL 


FIG.  21. — A  LEUKOCYTE  FROM  HUMAN  BLOOD  IN 

ACTIVE  AMEBOID  MOTION. 

The  figures  indicate  the  successive  forms  assumed 
by  the  cell.  Drawings  were  made  at  intervals  of  one 
minute.  X  500. 


(a)     Ameboid  motility  is  exemplified  in  the  movements  of  an  ameba  : 
hence  the  name.     This  consists  essentially  in  the  formation  of  a  proto- 
plasmic process  or  pseud  o  pod  in  ni .  into  which  the  main  mass  of  proto- 
n  A  r         plasm    flows,    thus    pro- 

ducing progression  (Fig. 
20).  The  movement  of 
the  white  blood-corpus- 
cles is  of  this  sort  (Fig. 
21). 

(b)  Ciliary  mot  Hi  I  >/ 
is  characteristic  of  hair- 
like  processes  of  certain 
cells;  such  processes  or 
cilia  represent  essentially  permanently  differentiated  delicate  pseudo- 
podia.  The  method  of  cilium  formation  is  illustrated  in  its  simplest 
form  in  the  transient  vibratory  processes  that  arise  under  certain  condi- 
tions on  leukocytes  (Fig.  225).  In  metazoa  generally  ciliated  cells  are 
attached,  motion  being  limited  to  the  cilia,  which  are  located  on  the  free 
border.  The  function  of  cilia  is  to  pro- 
pel secretions  toward  the  surface.  The 
motion  is  wavelike  and  always  in  one 
direction.  The  cilia  are  generally  at- 
tached to  a  double  row  of  granules,  the 
'basal  bodies'  (Fig.  22),  perhaps  parti- 
tion products  of  the  centrosome.  In 
Protozoa,  e.g.,  Paramecium  (Fig.  3), 
the  entire  surface  of  the  cell  may  be 
ciliated;  the  function  of  the  cilia  here 
being  progression,  and  the  direction  of 
stroke  is  reversible.  Certain  cilia  are 
non-motile,  e.g.,  in  the  epididymis, 
where  they  are  closely  clumped  into 
brushlike  masses  (Fig.  25).  The  func- 
tion of  such  cilia  is,  in  part  at  least,  to 
furnish  a  means  for  the  elimination  of 

secretions.  Flagellate  motion  is  to  be  regarded  as  a  variety  of  ciliary 
motion.  A  flagellum  is  commonly  regarded  as  a  more  robust  cilium. 
The  purpose  of  flagella  is  to  propel  the  cells  to  which  they  are  attached. 
Usually  in  higher  animals  the  number  of  flagella  is  limited  to  one  to  a 
cell.  The  best  examples  of  flagella  are  furnished  by  spermatozoa  (Fig.  23). 


FIG.  22. — THREE  CELLS  FROM  THE 
EPIDIDYMIS  OF  THE   RABBIT. 
The  non-ciliated  cell  has  a  diplo- 
some  at  its  free  border.     The  ad- 
jacent ciliated  cells  have  in  place  a 
double   row   of  'basal   granules'  to 
which  the  cilia  are  attached.  (Aft.*"- 
v.  Lenhossek.) 


VITAL  PROPERTIES  OF  CELLS  17 

(c)  Molecular  n/o/i/i/i/  is  a  dancing  or  oscillatory  movement  of  thr 
irniimlrs  in  living  protoplasm.     Such  granules  may  be  non-living  matter. 
pigment,  etc.     This  typo  of  motion  is  also  called  brow  man  movement. 
It  is  probably  purely  a  physical  phenomenon.     It  may  be  simulated  by 
mixing  finely  divided  carmin  with  glycerin. 

(d)  Circulatory  or  streaming  movement  is  present  in  various  de- 
grees in  probably  all  living  protoplasm.     It  is  only  when  it  is  rapid 
that  it  becomes  easily  discernible.    It  is  readily  demonstrable  in  certain 
cells,  e.g.,  chara  and  nitella;  also  less  readily  in  certain  protozoa  (Para- 
mecium).     It  must  most  probably  be  interpreted  as  a  form  of  respira- 
tion.    It  is  characterized  by  a  flowing 

or  streaming  of  the  protoplasmic  gran- 
ules in  a  definite  direction. 

(e)  The  reason  for  listing  muscu- 
lar as  a  separate  type  of  motility  is 
mainly   its   predominance    in   animals 
and  the  fact  that  it  does  not  apparently 
fully  conform  to  any  of  the  above  types. 

It    is    characterized    by    a    reversible  FlG.  23,-CiLiATE  AND  FLAGKLLATE 

process  of  contraction  of  specially  dif-  CELLS. 

ferentiated  muscle  fibrils.     It  perhaps  A,  ciliated  cells  isolated  from  the 

most  closely  resembles  streaming  motil-  trachea  of  a  cat;  B,  human  sperm*- 

..         T,L  i      -i    j.    i                 ^              •        •  tozoa — 1.    in    surface    view;    2,    in 

ity.    It  leaas  to  least  confusion,  m  view  profile    'Examined  fresh  in'normai 

of  our  present  lack  of  definite  knowl-     saline  solution.    X  550. 
edge  regarding  the  physical  and  chem- 
ical phenomena  underlying  muscular  motion,  to  speak  of  it  as  a  distinct 
type.     It  will  be  further  discussed  under  Muscle. 

(4)  Reproduction. — The  essence  of  reproduction  is  cell  multiplica- 
tion. A  living  cell  has  the  power  of  producing  other  cells  like  itself. 
Viewed  philosophically,  cells  may  conceivably  arise  in  two  different  ways: 
(1)  from  non-living  material,  spontaneous  generation  (abiogenesis)  ;  (2) 
from  preexisting  cells  by  division.  Science  has  quite  generally  accepted  the 
aphorism  'omnis  cellula  e  cellula'  (Virchow)  as  an  expression  of  the 
whole  truth.  However,  full  acceptance  of  the  doctrine  of  evolution  logi- 
cally compels  belief  in  spontaneous  generation :  this  not  in  any  such 
crude  form  as  that  frogs  may  arise  from  the  mud  of  rivers,  or  insect? 
from  dew  or  dung,  but  that  given  the  conditions  (conceivably  possible 
somewhere  in  the  universe  to-day)  prevalent  when  life  first  appeared  as 
the  original  mass  of  living  protoplasm,  the  'cytode'  or  'cytoblastema,'  the 
inorganic  may  continually  be  passing  into  the  primarily  organic,  e.g., 
3 


18 


INTRODUCTION— PEOTOPLASM— CELL 


monera  (Haeckel),  but  not  perceptible  under  our  present  means  of 
search  and  observation.  This  is  the  position  urged  by  one  of  the  leading 
physiologists  and  histologists  (E.  A.  Schaefer)  of  our  day,  following 
Spencer  of  the  preceding  generation. 

However,  in  histology  we  need  be  concerned  only  with  the  derivation 
of  cells  from  preexisting  cells.  This  proceeds  in  one  of  two  ways:  (a) 
direct,  amitotic,  or  akaryokinetic ;  and  (b)  indirect,  mitotic,  or  karyokin- 
etic.  The  difference  between  the  two  inheres  in  a  difference  in  behavior 
on  the  part  of  the  nucleus  (or  karyon).  Comparative  studies  of  the 


FIG.  24. — SUCCESSIVE  STEPS  IN  AMITOTIC  DIVISION  ix  TEXDON  CELL  OK  XEW-BORN 

MOUSE. 
(After  Nowikoff.     X  800.) 


lower  groups  of  animals  and  plants  have  revealed  a  fairly  complete  series 
of  intermediate  stages.  .  On  the  basis  of  these  facts  it  is  believed  by  some 
(e.g.,  Strasburger)  that  amitosis  is  the  primitive  method  of  cell 
multiplication,  mitosis  the  derived  or  more  highly  specialized  type. 
Others  regard  amitosis  as  the  derived,  not  the  primitive  form  of 
division. 

Cell  division  is  presumably  due  to  the  fact  that  the  area  of  the 
surface  increases  as  the  square,  the  volume  as  the  cube,  of  the  diameter. 
In  consequence,  the  periphery  becomes  more  favorably  placed  with  respect 
to  the  nutritive  medium  than  the  more  central  portions.  The  time  then 
arrives  when  the  center  must  suffer  nutritive  want  or  when  the  nucleus 
becomes  unable  to  exert  its  trophic  functions  at  the  distance  of  the  ad- 


VITAL  PROPERTIES  OF  CELLS 


11) 


vancing  periphery.  Division  of  such  an  enlarged  cell  into  two  smaller 
cells  reestablishes  the  original  and  more  favorable  nucleo-cytoplasmic 
dimensional  relationship. 

(a)     AMITOSIS. — In  typical  amitosis  the  nucleolus  first  becomes  bi- 
lobed  and  then  divides  (Fig.  24).    This  is  followed  by  nuclear  division, 


FIG.  '25.— Succ^ssivs  STAGES  IN  THE  AMITOTIC  DIVISION  OF  THE  CILIVT:D  C^..i 
LINING  THE  DUCTULI  EFFEUENTES  OF  THE  EPIDIDYMIS  OF  THE  Mousa.     x  15  i). 


each  resulting  nucleus  enclosing  one  of  the  nucleoli.    Nuclear  division  is 
followed  by  cytoplasmic  division.     A  centrosome  is  generally  neither 
active  nor  even  visible  during  this  process.     This  typical  condition  is 
rarely  realized.    It  Avas  first  described  by  Remak  (1841)  for  blood-cells. 
Usually  nuclear  division  is  in- 
dependent of  nucleolar  fission, 
which   may  be   lacking    (Fig. 
25).     The  nuclear  fission  pro- 
ceeds variously  by  a  medial  or 
submedial     annular     constric- 
tion, or  by  progressive  linear 
indentation  of  some  portion  of 
the    surface.      In    certain    in- 
stances the  division  takes  place 
inside  of  the  original  nuclear 
membrane.    The  nuclear  prod- 
ucts may  be  of  unequal  size, 
and  multiple  (Fig.  26).    Gen- 
erally cytoplasmic  division  lags      FlG'    26.-MULTINUCLEATED    GlANT    CELL, 

.         ,     ,   .      ,  ,  n.     .    .  FROM     THE     YOLK-bAC     OF   A    10    MM.      rlG 

tar  behind  nuclear  division,  or        EMBRYO.   X  2000. 
may  even  fail  to  appear,  thus 

producing  bi-  or  multinucleate  cells.  Amitosis  effects  a  mass  division  of 
the  nucleus ;  neither  spireme  nor  chromosome  nor  achromatic  spindle,  so 
conspicuous  in  mitosis,  appear.  Until  quite  recently  amitosis  was  gen- 
erally regarded  as  a  relatively  rare  and  unimportant  process.  It  was 


20 


INTRODUCTION— PEOTOPL  ASM— CELL 


supposed  to  be  associated  only  with  highly  specialized  and  pathological 

conditions  leading  inevitably  to  death.     Cells  once  having  Buffered  ami- 

totic  division  were  believed  not  to  be  capable  of  thereafter  dividing  mitot- 

ically.    The  work  of  Child  (Biol.  Bull.,  1007)  has  shown,  however,  that 

it  is  probably  of  very  wide  occurrence.    Instances  have  been  described  in 

most  of  the  animal  groups,  including  the  vertebrates.     Child  has  shown 

its  occurrence  in  regions  of  rapid  growth,  as  in  various  embryonic  tissues, 

e.g.,  blastoderm  of  chick  (Patterson),  and  where  a  secretion  is  elaborated 

or  in  places  of  reserve  formation.    .These  facts  may  be  harmonized  with 

its  occurrence  in  starving,  degenerating  tissues  on  the  basis  of  a  common 

x  underlying  condition,  namely, 

relative    scarcity    of    nutritive 

material.      Wieman    conceives 

\       -.s&^lfeSfa.  °^  amitosis  as  due  to  scarcity 

I  *    *  *  *  •  'of  oxygen  supply. 

-**     *•'_  Where  mitosis  and  amitosis 

\  .  *  *  *  (MRMI    J 

'   ^  are  simultaneously  present,  it 

*»  ^^      is    more    frequently    the    cells 

with  the  large  nuclei,  sur- 
rounded by  a  considerable 
amount  of  undifferentiated  "cy- 
toplasm, that  divide  by  mitosis. 
The  factors  underlying  amito- 
sis most  probably  exert  their 
final  effect  indirectly  through 
initial  influence  upon  the  cen- 
trosome.  The  v  best  experi- 
mental evidence  in  favor  of 
this  view  is  supplied  by  Xathansolm  who  grew  Spirogyra,  normally 
dividing  by  mitosis,  in  a  1  per  cent,  solution  of  ether  in  water,  when 
the  cells  divided  amitotically.  On  transference  to  pure  water,  the  cells 
again  divided  mitotically.  The  ether  seems  to  have  exerted  a  'stupe- 
fying' effect  upon  the  kinoplasm  (centrosome  material),  compelling 
division  by  amitosis.  Amitosis  is  now  generally  conceded  to  be  of 
wide  occurrence  under  certain  conditions  and  in  certain  cells,  but  it  is 
still  quite  unanimously  disbelieved  to  occur  in  germ  cells.  In  the  lat- 
ter it  has  perhaps  not  yet  been  certainly  demonstrated  to  occur  in  cells 
actually  in  the  germ  cycle.  In  Mammalia  amitosis  can  be  demonstrated 
in  the  intermediate  layers  of  stratified  squamous  (skin),  transitional 
(bladder)  and  certain  ciliated  (epididymis,  Fig.  25)  epithelia;  in  the 


*«'*%* 

FIG.   27. — SPERMATOCYTE    OF   PYERIS   CRA- 
TEGI,  A  BUTTERFLY,   SHOWING  A  CILIUM 
ATTACHED  TO  THE  CENTROSOME. 
(After  Meves.) 


FIG.  28. — DIAGRAMS  ILLUSTRATING  SUCCESSIVE  STAGES  OF  MITOSIS. 

A-F,  prophase;  G,  metaphase;  H,  anaphase;  I-J,  telophase.  a,  achromatic 
spindle;  c,  centrosome;  ep,  equatorial  plate  of  chromosomes;  if,  interzonal  fibers; 
ft,  nucleolus.  (After  Wilson.) 

21 


22 


INTKODUCTION— PEOTOPLASM— CELL 


medulla  of  the  adrenal,  and  in  decidual  cells.     In  ciliated  epithelia  this 

mode  of  division  is  perhaps  associated  with  a  partition  of  the  centro- 

some  in  the  formation  of  cilia.     This  will  be  further  discussed  under 

a  Ciliated    Epithelia. 

This  view  is  sup- 
ported by  the  fact 
that  the  flagella  of 
spermatozoa  arise 
from  the  centro- 
some,  and  the  ob- 
servation that  in 
certain  cells  the 
centrosome  of  mi- 
totic  spindles  de- 

c°ia 


FIG.  29.—  CELLS  FROM  EPIDERMIS  OF  THE  SALAMANDER, 
Three  cells  are  in  process  of  division  by  mitosis,  a, 
prophase;  b,  anaphase.  The  second  cell  above  b,  whose 
cell  body  is  in  process  of  fission,  presents  a  stage  of  the 
telophase.  (After  Wilson.) 


(b)  MITOSI,- 
•This  is  the  prevail- 
ing type  of  cell  di- 
vision.  For  con- 
venience  of  descrip- 
tion  the  process 

whlch       must       of 
course   be   thought 

of  as  continuous,  may  be  divided  into  (1)  prophase;  (2)  metapliase;  (3) 
anaphase;  and  (4)  telophase.  An  alternative  and  preferable  terminology 
employs  the  words  anaphase  (prophase),  mesophase  (metaphase)  and 
kataphase  (anaphase  and  telophase).  These  phases  involve  coincident 
changes  in  the  nucleus  and  the  archoplasm  (attraction  sphere,  Fig.  28,  A 
to  J).  Mitotic  figures  can  be  seen  in  all  rapidly  growing  tissues.  The 
process  is  an  essentially  similar  one  throughout  the  plant  and  animal 
kingdoms;  variations  relate  only  to  details  associated  chiefly  with  the 
archoplasm.  The  most  favorable  locations  for  study  of  mitosis  are  the 
growing  tips  of  roots  of  certain  plants,  e.g.,  onion,  hyacinth,  dogtooth 
violet;  amphibian  tissue  (particularly  skin  and  blood-cells),  and  the 
testes  of  grasshoppers.  Mitosis  in  germ  cells  involves  certain  specialized 
features,  and  calls  for  additional  theoretical  consideration  ;  hence  the 
description  of  these  maturation  mitoses  will  be  reserved  for  the  chapter 
dealing  with  the  ovaries  and  testes,  Avhere  a  complete  account  will  follow. 
Among  the  simplest  types  of  mitosis,  and  those  best  adapted  for  labora- 


FIG.  30.— SUCCESSIVE  STAGES  OF  MITOSIS  IN  THE  ROOT  TIP  OF  THE  DOGTOOTH  VIOLET 

(ERYTHRONIUM  AMERICANUM). 

a,  resting  nucleus;  b,  close  spireme;  c,  loose  spireme;  d,  segmented  spireme;  e,  late 
prophaso;/  and  g,  metaphase;  h  and  i,  anaphase;  jW,  telophase  (showing  mid-body  or 
cell  plate)  ;jn  and  n,  daughter  cells,  n,  with  resting  nuclei.  X  1500. 

23 


24:  INTRODUCTION— PKOTOPLASM— CELL 

tory  study,  at  least  as  an  approach  to  the  subject,  is  that  shown  in  the 
root  tip  of  the  dogtooth  violet  (Fig.  30,  a  to  n).  The  cells  and  the  mi- 
totic  figures  are  here  so  large  that  all  the  major  details  can  be  easily 
recognized  by  use  of  the  usual  dry  high  power  lenses  of  the  microscope. 
(1)  Prophase. — This  stage  can  again  be  subdivided  into  that  (a) 
of  the  resting  nucleus;  (b)  of  the  nucleus  with  dose  spireme;  (c)  of  the 
nucleus  with  the  loose  spireme;  and  (d)  of  the  segmented  spire  in  >• 
Coincident  with  these  nuclear  changes,  the  centrosome  in  animal  cells 
divides  into  two  (diplosome) ;  these  moieties  move  apart  toward  opposite 
poles  of  the  nucleus  and  build  a  spindle  (amphiaster)  between  them- 
selves. Meanwhile  the  nuclear  membrane  begins  to  disappear,  only  a 
remnant  distant  to  the  achromatic  spindle  persisting  at  the  end  of  the 
prophase.  In  the  root  tip  cell  of  the  dogtooth  violet  and  in  plant  cells 
generally,  the  spindle  appears  in  less  conspicuous  fashion  than  in  animal 
cells.  A  centrosome  is  apparently  lacking.  The  first  indications  of  the 
spindle  are  the  polar  caps  of  faint  radiations  which  grow  medially  to  build 
the  spindle.  The  resting  nucleus  (Fig.  30,  a)  is  characterized  by  a 
random,  granular,  nuclear  reticulum  with  net-knots  and  one  or  several 
nucleoli.  This  reticulum  becomes  changed  into  a  delicate,  deeply  chro- 
matic, probably  continuous,  close  spireme  (Fig.  30,  b).  By  process  of 
shortening  and  thickening,  this  changes  into  the  loose  spireme  stage 
(Fig.  30,  c).  The  nucleoli  have  meanwhile  contributed  chromatic  sub- 
stance to  the  spireme,  but  may  persist  for  some  time  longer  as  achro- 
matic, ultimately  fragmenting  or  dissolving,  bodies.  On  closer  inspection 
the  close  spireme  is  seen  to  consist  of  a  series  of  granules  (chromomeres) ; 
during  the  loose  spireme  stage  these  become  split,  thus  giving  rise  to 
a  double  row  of  granules.  The  loose  spireme  passes  into  the  succeeding 
stage  (segmented  spireme,  Fig.  30,  d)  by  transverse  segmentation  inco  a 
number  of  rods  or  chromosomes.  At  this  stage  all  indication  of  chro- 
momeres  is  generally  again  lost,  the  chromosomes  appearing  as  compact, 
deeply  staining  rods  of  various  shapes. 

The  number  of  chromosomes  is  believed  to  be  constant  for  all  cells  of 
a  species.  This  belief  rests  upon  data  of  actual  counts  in  various  insects  and 
other  lower  animals  and  certain  plant  forms.  Here  the  number  is  rela- 
tively small,  and  the  individual  chromosomes  are  large  and  can  in  conse- 
quence be  readily  counted.  (Certain  qualifying  statements  must  be  made 
in  the  chapter  which  includes  a  discussion  of  sex  determination.)  Attempts 
have  recently  been  made  to  throw  doubt  upon  the  matter  of  a  .specific  chro- 
mosome constancy,  but  it  is  only  fair  to  note  that  these  attempts  have 
dealt  with  relatively  unfavorable  material,  where  exact  chromosome  counts 


VITAL  PROPERTIES  OP  CELLS  25 

are  extremely  difficult  if  not  at  present  actually  impossible.  It  may  be 
noted  in  passing  also,  that  the  chromosomes  are  believed  by  many  to  be  the 
bearers  of  the  determiners  of  hereditary  characters — a  point  to  be  further 
discussed  below. 


(2)  MetapJiase. — This   is  a  relatively  brief  stage   in  mitosis.     It 
includes  the  period  when  the  chromosomes  are  arranged  upon  the  spindle 
in  the  equatorial  plate.     Seen  in  polar  view  this  is  called  the  monastcr 
stage  (Fig.  30,  e).     In  this  stage  the  chromosomes  split  longitudinally. 
In  dogtooth  violet  the  number  of  chromosomes  is  twenty-four.     A  com- 
mon form  of  chromosome  is  the  U-shaped  type.    The  point  of  attachment 
to  the  spindle  is  the  apex  of  the  bent  chromosome  (Fig.  30,  f).     In  the 
more  rapidly  growing  cells  the  double  or  split  condition  of  the  chromo- 
somes has  remained  discernible  since  the  preceding  telophase,  a  true 
resting  stage  having  been  omitted.     At  metaphase  the  already  longi- 
tudinally   split    chromosomes    are    completely    divided,    and    the    sepa- 
rated moieties    (daughter  chromosomes)    drawn  toward  opposite  poles 
(Fig.  30,  g). 

(3)  Anapliase. — The  limits  of  this  phase  are  indefinite  (Fig.  30, 
h  to  j).     It  may  be  said  to  include  all  stages  between  that  when  the 
separation  of  the  daughter  chromosomes,  resulting  from  the  longitudi- 
nally splitting  of  the  mother  chromosomes,  is  severally  consummated, 
and  that  when  the  groups  of  daughter  chromosomes  drawn  to  either  pole 
are  still  distinct.     Seen  in  side  or  oblique  view  the  later  stages  of  this 
phase    present    a    double    star    arrangement    of    chromosomes; — hence 
diaster  stages    (Fig.    30,   i).      The   daughter    chromosomes,   an   equal 
number  at  either   pole,  were   drawn   apart  by   activity  of   the  outer- 
most of  the  spindle  fibers  (called  mantle  fibers)   presumably  by  process 
of  contraction.     The  inner  or  'interzonal  fibers'  constitute  the  central 
spindle. 

(4)  Telophase. — Meanwhile  a  plate  of  granules   (cell  plate;  mid- 
body]  has  appeared  in  the  equatorial  region  of  the  spindle.    This  marks 
the  plane  of  the  future  division  (Fig.  30,  j  and  k).    In  animal  cells,  an 
annular  constriction  appears  peripherally  in  the  cell  membrane.     This 
proceeds  centrally  throughout  telophase  until  ultimately  the  mother-cell 
is  divided  into  two  daughter-cells.    The  constriction  of  the  cells  in  divi- 
sion is  generally  interpreted  as  a  phenomenon  of  alteration  in  surface 
tension.     Coincidently  with  the  steps  of  this  process,  the  chromosomes 
and  centrosomes  (archoplasm  material  in  plants)  pass  through  the  stages 
of  the  prophase,  but  in  inverse  order:  segmented  spireme,  loose  spireme. 


/  g 

FIG.  31. — SUCCESSIVE  STAGES  IN  THE  MATURATION,  FERTILIZATION  AND  SEGMENTA- 
TION OF  THE  STARFISH  (ASTERIAS  FORBESII)  EGG. 

a,  first  maturation  spindle  (m.s.l)  and  the  spermatozoon  (s);  b,  formation  of  the 
first  polar  body  (p.b.l)  and  the  residual  substance  of  the  nucleus  (r.s.);  c,  second 
maturation  spindle  (m.s.2);  d,  female  pronucleus  (  ?  ) ;  e,  union  of  male  (  3  )  and  female 
pronuclei  (the  male  pronucleus  is  derived  from  the  spermatozoon) ;  /,  first  segmenta- 
tion spindle;  g,  two-cell  stage  of  division,  d  and  e  are  less  highly  magnified. 

26 


HISTOGENESIS  27 

close  spireme,  resting  daughter  nucleus  with  its  daughter  centrosome 
and  ultimately  a  nucleolus  (Figs.  30,  k,  1,  m,  n).  Where  a  cell  plate 
appears,  division  is  consummated  without  constriction.  In  'certain 
pathological  tissues,  e.g.,  cancers,  the  cells  divide  in  various 
atypical  ways,  involving  the  formation  of  tri-  and  multipolar  spin- 
dles. 


HISTOGENESIS 


Every  higher  organism  begins  as  a  fertilized  egg  or  zygote;  this  in- 
volves the  fusion  of  a  male  (spermatozoon)  and  a  female  (egg)  germ  cell 
(Fig.  31,  a  and  e).  The  result  of  the  fusion  is  a  mingling  of  approxi- 
mately equal  parts  of 
paternal  and  mater- 
nal chromatin  (pre- 
sumably the  basis  of 
specific  heredity),  a 
large  mass  of  mater- 
nal cytoplasm  and 
nutritive  substance 
with  a  small,  but 
perhaps  important 
mass  of  male  cyto- 
plasm; and  a  coinci- 
dent stimulus  to  de- 
velopment. The  fer- 
tilized egg  divides  by 
mitosis  into  two 
spheroidal  cells — the 
typical  embryonic 
form — or  blastomeres 


FIG.  32. — TRANSVERSE  SECTION  OF   A   FROG  EMBRYO, 

SHOWING  THE  THREE  GERM  LAYERS. 
a,  neural  crest;  b,  neural  groove;  c,  neural  plate;  d> 
(Fig.  31,  f  and  g),  coelom;  e,  ectoderm;/,  mesoderm;  g,  entoderm;  h,  somite; 
and  each  of  these  *>  n°tochord;  j,  parietal  mesoderm;  A;,  visceral  meso- 
derm; I,  yolk;  central  opening,  the  primitive  intestine. 
(Drawing  by  G.  A.  Pagenstecker.) 


again  into  two,  the 
segmentation  process 
continuing  until  the  adult  organism  results  as  an  aggregation  of  innumer- 
able cells.  This  process  of  growth  through  cell  multiplication  is  accom- 
panied by  cell  differentiation,  which  constitutes  histogenesis.  The  first 
outstanding  stage  in  the  differentiation  is  that  when  the  three  funda- 


28  INTRODUCTION— PEOTOPLASM— CELL 

mental  germ  layers:  ectoderm  (ectoblast;  epiblast),  mesoderm  (meso- 
blast),  entoderm  (endoblast;  hypoblast)  have  appeared  (Fig.  32).  Back 
of  this  of  course  must  lie  a  more  fundamental  differentiation,  perhaps 
already  present  in  the  unfertilized  egg,  a  predelineation  of  adult  struc- 
ture destined  to  develop  from  localized  egg  materials.  By  the  process  of 
histogenesis  all  the  adult  tissues  arise  from  the  several  germ  layers.  This 
matter  is  summarized  in  the  following  table : 


ADULT    TISSUE    DERIVATIVES    FROM 


ECTODERM 

Epidermis  and  its  de- 
rivatives :  hair,  nails, 
and  epithelium  of  se- 
baceous, sweat  and 
mammary  glands. 

Epithelium  of  mouth 
and  its  derivatives : 
enamel.  taste  buds, 
epithelium  of  salivary 
and  other  b  u  c  c  a  1 
glands,  and  anterior 
portion  of  hypophysis. 

Epithelium  of  anus, 
and  distal  portion  of 
the  male  urethra. 

Epithelium  of  nos- 
trils and  communicat- 
ing glands  and  cranial 
sinuses. 

Epithelium  of  con- 
junctiva and  associated 
ducts  and  lacrimal 
glands.  The  lens,  and 
the  epithelium  of  the 
pars  nervosa,  ciliaris 
and  iridica  retinas. 

Epithelium  of  mem- 


Epithelium  of  urinif- 
erous  tubules,  renal 
pelves  and  ureters. 

Epithelium  of  the 
seminiferous  tubules 
and  the  associated  ex- 
cretory ducts  of  the  tes- 
tis;  epithelium  of  ovi- 
duct and  uterus ;  prob- 
ably also  the  sex  cells. 
The  cortex  of  the  su- 
prarenal gland.  All 
muscular  tissue ;  con- 
nective tissue ;  vascular 
tissue  (blood  and 
lymph  ve-sscls  and 
cells),  and  lymphoid 
organs  in  general. 

Epithelium  (meso- 
thelium)  of  pleurae, 
pericardium  and  peri- 
toneum; of  the  tendon 
sheaths,  joint  cavities 
and  bursa3;  and  of  the 
chambers  of  the  eye, 
and  the  p  e  r  i  1  y  m  p  h 
spaces  of  the  internal 


Epithelium  of  diges- 
tive tract  (including 
pharynx;  excluding 
mouth  and  anus)  and 
associated  glands: 
pharyngeal,  esophageal, 
gastric,  intestinal,  pan- 
creas and  liver,  with 
gall-bladder. 

Epithelium  of  middle 
ear  (tympanum)  and 
auditory  (Eustachian) 
tube.  Epithelium  of 
respiratory  system,  be- 
yond nostril.  Epithe- 
lium of  thyroid,  para- 
thyroids, and  the  thy- 
mic  reticulum  and  cor- 
puscles. 

Epithelium  of  female 
urethra,  proximal  part 
of  male  urethra,  and  of 
the  urinary  bladder. 

Epithelium  of  pros- 
tatic  and  Cowper's 
glands  in  the  male, 
and  of  the  glands  of 


CYTOMOBPHOSIS 


K<  ToOERM 

branous  labyrinth  of 
internal  car,  and  lining 
of  external  ear. 

Epithelium  lining 
the  central  canal  of  the 
spinal  cord,  and  the 
ventricles  of  the  brain. 

All  neurons  and  neu- 
roirlia  of  the  nervous 
system. 

Certain  ductless 
glands :  pineal,  posteri- 
or (nervous)  portion  of 
hypophysis,  medulla  of 
suprarenal,  and  the 
chromaffin  system  or 
paraganglia. 

Possibly  smooth  mus- 
cle associated  with 
sweat  glands,  and  in 
iris  of  eye. 


c  ir  ( .-cal;i'  tyinpani  and 
vestibuli). 


Bartholin     in    the    fe- 
male. 

Xtulei  pulposi  of 
intervertebrul  discs.,  re- 
nv.ii  s  of  the  embryonic 
r.oto  ho-d.  (Ofer-toder- 
iml  origin  h  the  guinea 
pig,  according  to  G. 
Carl  Huber;  Anat. 
Rec.,  Vol.  14,  p.  217, 
1918.) 


CYTOMORPHOSIS 


From  the  standpoint  of  the  individual  cells  of  tissues,  histogenesis 
involves  progressive  and  regressive  changes.  This  process  may  be  desig- 
nated as  cytomorphosis  (Minot).  The  gradual  acquirement  of  definite 
form  by  development  is  known  as  morphogenesis.  Cytomorphosis  in- 
cludes several  successive  steps:  (a)  undifferentiated  or  embryonal  stages; 
(b)  differentiated  stage,  during  which  the  cell  acquires  and  maintains  its 
maximum  differentiation — expressed  structurally  by  a  definite  shape  and 
specific  content — and  performs  its  specific  function;  (c)  regressive,  when 
the  function  gradually  wanes,  and  finally  fails  (reflected  in  coincident 
protoplasmic  alterations),  the  cell  concerned  suffering  death  and  ulti- 
mately removal  from  the  body. 

With  this  preliminary  general  view  of  protoplasmic  organization  and 
function  (general  cytology)  we  arc  prepared  to  approach  histology  proper. 


CHAPTER   II 
EPITHELIAL    TISSUES 


TISSUES 

A  tissue  in  the  histologic  sense  is  a  collection  of  similarly  specialized 
cells  united  in  the  performance  of  a  particular  function,  e.g.,  liver  tissue. 
In  certain  tissues  the  cells  are  joined  together  by  an  intercellular  cement 
substance,  which  is  a  secretion  product  of  the  cells  themselves. 
Through  this  cement  may  extend  the  so-called  'intercellular  bridges'  or 
cytodesmata  (Fig.  33),  the  minute  intervening  spaces  forming  delicate 


FIG.    33. — GROUP    OF    EPITHELIAL    CELLS    FROM  THE   MALPIGHIAN   LAYER    OF 

THE  SKIN. 
The  intercellular  bridges  are  very  distinct.     Hematein  and  eosin.     X  1,000. 

canaliculi,  presumably  for  mediating  the  transfer  of  nutritive  material 
from  cells  more  favorably  placed  with  respect  to  the  source  of  supply  to 
those  less  favorably  located,  e.g.,  epidermis;  these  bridges  arise  through 
process  of  vacuolization  in  the  exoplasm  of  adjoining  cells,  the  walls 
of  the  original  vacuoles  persisting  as  'bridges.'  Through  such  bridges, 
fibrils  may  extend  from  cell  to  cell.  Practically  every  tissue  contains 

30 


TISSUES  31 

also  connective  tissue  elements  for  unification  and  support;  also  vascular 
and  nervous  constituents.  Tissues  in  which  the  cell  boundaries  are  ab- 
sent are  known  as  nyncyt'm  (Fig.  :U).  A  syncytium  may  obviously  arise 

through  nuclear  proliferation  in  the  ab- 
sence of  cytoplasmic  division,  or  as  the 
»  result  of  the  disappearance  of  original 

cell  boundaries.     We  may  distinguish 


FIG.  34. — A  VILLUS  OF  THE  HUMAN 
PLACENTA,  SHOWING  A  PERIPH- 
ERAL SYNCYTIUM  OF  IRREGULAR 
THICKNESS. 
The    connective    tissue    inclosed 

by  the   syncytium    contains  three 

capillary  vessels.      Hematein   and 

eosin.     X  500. 


FIG.  35. — CELLS  FROM  THE  PANCREAS  OF 
NECTURUS,  CONTAINING  SECRETORY  GRAN- 
ULES AND  BASAL  ERGASTOPLASMIC  FILA- 
MENTS. (After  Matthews.) 


the  following  fundamental  tissues :  (a)  epithelial;  (b)  connective;  (c) 
muscular;  (d)  nervous;  and  (e)  vascular. 

Lymphoid  tissue  may  be  regarded  as  still  another  fundamental  tissue; 


FIG.  36.— VARIOUS  FORMS  OF  CELLS. 

a,  squamous  epithelium  from  the  tongue;  b,  a  columnar  cell  from  the  small  intestine; 
c,  a  polyhedral  or  spheroidal  cell  from  the  liver;  d,  a  smooth  muscle  cell  from  the  mus- 
cular coat  of  the  stomach.  X  550. 


or  it  may  be  included  under  vascular  tissue.  In  fact  from  the  genetic 
viewpoint,  vascular  may  be  included  under  connective  tissue,  since  both 
arise  from  the  mesenchyma. 


EPITHELIAL  TISSUES 


Bepresentatives  of  all  of  the  fundamental  tissues  are  generally  found 
in  all  histologic  preparations,  or  tissues  in  a  general  sense.  Cells  vary 
greatly  both  from  the  standpoints  of  shape  and  contents  in  the  various 
tissues — both-  depending  upon  the  types  and  phases  of  function.  The 
more  usual  form  variations  include:  (a)  spheroidal,  spherical  (e.g.,  em- 
bryonic cells  and  egg  cells,  Fig.  1,  chap.  1),  polyhedral  (spherical  cells 
modified  by  pressure  from  adjacent  cells,  e.g.,  liver  cells,  Fig.  37)  ;  (b) 
scalelike  or  squamous  (e.g.,  super- 
ficial cells  of  mucous  membrane  of 
mouth,  Fig.  36,  a) ;  (c)  columnar, 
prismatic  or  cylindrical  (e.g.,  cells 
lining  intestine,  Fig.  38.  b).  Col- 
umnar cells,  when  very  short,  are 


FIG.    37.  —  POLYHEDRAL    EPITHELIUM, 
FROM    A    SECTION    OF    THE    HUMAN 
LIVER. 
The  central  blood  capillary  contains 

one  leukocyte,  and  its  wall  contains  the 

nucleus  of  a  flattened  endothelial  cell. 

Hematein  and  eosin.     X  550. 


FIG.  38. — GOBLET  AND  COLUMNAR  CELLS 
FROM  THE  LARGE  INTESTINE  OK  THE 
CAT. 
A,  Goblet  cells;  B,  isolated  columnar 

cells.     X  900. 


usually  designated  cubical  or  cuboidal  (e.g.,  bronchioles  and  rete  testis, 
Fig.  43)  ;  intermediate  lengths  may  be  designated  either  tall  cuboidal  or 
short  columnar;  when  modified  by  confinement  in  an  alveolus  into  a 
pyramidal  shape  as  in  glands,  they  may  be  called  pyramidal  or  'glandu- 
lar' (Fig.  46).  Glandular  cells,  moreover,  are  characterized  also  by  an 
internal  differentiation  commonly  expressed  in  the  form  of  granules  or 
filaments.  Columnar  cells  may  be  further  modified  by  the  appearance  of 
cilia  into  ciliated  epithelium  (e.g.,  trachea,  bronchial  tube.  Fig.  52),  or  of 
mucus  into  goblet  cells  or  'unicellular  glands'  (e.g.,  intestine,  Fig.  38,  a)  ; 
or  as  specialized  receptors  for  stimuli  of  special  sense  they  may  become 
modified  as  neuro-epithelium  (e.g.,  certain  cells  of  eye,  ear,  nose  and 
tongue). 


EPITHELIAL  TISSUES  33 


EPITHELIAL    TISSUES 

Epithelia  are  cellular  membranes  covering  the  surfaces  and  lining 
the  internal  cavities  of  the  body.  They  serve  for  protection,  secretion,  ex- 
cretion, and  the  reception  of  stimuli.  The  constituent  cells  may  be  of  any 
of  the  above  enumerated  forms*1  The  spheroidal  types,  however,  are 
found  only  in  embryonal  membranes.  The  term  spheroidal  epithelium 
is  sometimes  employed  to  designate  masses  or  solid  columns  of  spheroi- 
dal cells,  such  as  appear  in  the  sex  cords  of  the  developing  testis  and 
ovary,  and  in  the  early  stages  of  glands.  They  are  in  general,  outgrowths 
or  evagination  from  embryonic  or  undifferentiated  epithelia. 

An  epithelium  may  consist  of  a  single 
layer  of  cells,  when  it  is  called  non-strat- 
ified or  simple  epithelium.     A  complete 
description,    however,    must    include    the 
name  of  the  preponderating  type  of  cell, 
e.g.,  simple  columnar  epithelium,  or  sim- 
pie  squamous  epithelium,  as  the  case  may 
be.     Moreover,  an  epithelium  may  consist      FIG.    39.— COLUMNAR    EPITHE- 
of  several  or  many  ]ayers,  ,vhen  it  becomes 
a  complex  or  stratified  epithelium.     The          (Profile  view.) 
uppermost  type  of  cells  gives  the  name  to         Hematein  and  eosin.    X  550. 
stratified  epithelium;  for  example,  in  the 

epidermis  the  outermost  cell  is  of  the  squamous  type,  though  the  middle 
cells  are  polyhedral,  and  the  innermost  columnar ;  hence  called  stratified 
squamous  epithelium  (Fig.  49). 

In  the  stratified  epithelia  the  superficial  cells  arise  through  cell  divi- 
sion in  the  deeper  layers,  and  if  they  become  detached  by  abrasion,  dis- 
integration, or  by  other  physiological  or  pathological  processes,  they  may 
be  replaced  by  cell  reproduction  occurring  in  the  lower  layers.  When 
but  a  single  layer  of  cells  is  present,  as  in  the  simple  epithelia,  loss  of 
cells  over  large  areas  will  obviously  become  more  difficult  of  replacement 
by  cell  division.  Hence  it  is  that  repair  of  extensively  destructive  patho- 
logical conditions  involving  such  epithelial  tissues  becomes  exceedingly 
difficult  and  often  impossible,  as,  for  example,  in  the  alveoli  of  the  lung. 

Each  epithelial  cell  is  to  some  extent  a  secreting  cell.     Sometimes 

secretion  is  its  chief  function,  as  is  the  case  with  goblet  cells,  which 

might  well  be  called  'unicellular  glands,'  and  which  secrete  abundant 

mucus.    The  same  is  true  of  those  cells  which  form  the  parenchyma  of 

4 


34 


EPITHELIAL    TISSUES 


secreting  glands salivary  gland?,  kidney,  and  liver.     In  many  epithelia 

secretion  is  a  subsidiary  function,  protection  being  the  primary  purpose. 

In  all  epithelia  a  cement  substance  is  present  between  the   cells. 

This  becomes  especially  abundant  and  dense  between  the  distal  ends  of 

ilir  cells  (if  columnar  epithelium,  and 
ig  nere  known  as  tertninal  bars  (Fig. 
40).  Cement  substance  has  the  pe- 
culiar property  of  precipitating  sil- 
ver nitrate  from  solutions,  which 
turns  black  on  exposure  to  sunlight. 
This  furnishes  an  especially  favor- 
able technic  for  demonstrating  cell 
boundaries.  All  epithelia,  simple  or 
stratified,  rest  upon  a  homogeneous 
basement  membrane  or  membrana 
propria,  frequently  a  product  of  the 
cells  themselves  but  occasionally  of 
connective  tissue  origin,  and  a  sub- 
jacent connective  tissue  supporting 
membrane  or  tunica  propria  (or 
corium).  The  latter  only  contains 

blood  and  lymph  vessels  from  which  the  epithelial  cell  must  draw  nour- 
ishment by  process  of  absorption,  and  transfer  through  'intercellular 
bridges.'  It  furnishes  support  also  for  the  nerve  supply.  We  may  now 
consider  briefly  the  usual  types  of  simple  and  stratified  epithelia.  The 
main  facts  are  summarized  in  the  appended  outline: 


FIG.  40. — 'TERMINAL  BARS'  OF  CEMENT 
SUBSTANCE  AS  SEEN  BETWEEN  THE 
EPITHELIAL  CELLS  OF  A  TUBULAR 
SECRETING  GLAND  IN  THE  PYLORIC 
REGION  OF  THE  HUMAN  STOMACH. 
The  columnar  epithelium  is  seen  in 
profile  at  a;  at  b,  the  free  ends  of  the 
cells  are  seen.    Hematein.    X  550. 


CLASSIFICATION    OF    EPITHELIA 

I.  SIMPLE  (XON-STBATIFIED)  EPITHELIA— those  which  (op- 
pose a  membrane  but  one  cell  in  thickness.  Epithelial  cells, 
usually  spherical  or  polyhedral  in  shape,  occur  also  en  masse 
in  the  form  of  cords  or  clusters. 


Squamous, 
composed  of 
flattened, 
scale-like 
cells. 


(a)  Lining  closed  cavities. 
Pavement  epithelium 

or  (1)  endothelium;   heart,   arteries,   capillaries,  veins, 
and  lymphatic  vessels. 

(2)  mesothelium;  serous  membranes. 

(3)  mesenchymal    epithelium;   synovial    membranes, 

bursa3,  and  tendon  sheaths,  lining  of  the  anterior 


EPITHELIAL  TISSUES 


36 


1.   Squamous, 
composed  of 
flattened, 
scale-like 
cells. 


9    Columnar. 


chamber  of  the  eye,  and  of  the  perilymph  spaces 
of  the  internal  ear. 

(b)  -Lining  the  alveoli  of  the  lungs,  some  tubules  of 

the  kidney,  the  middle  ear,  and  the  membranous 
labyrinth  of  the  internal  ear. 

(c)  As    the    superficial    cells    of   stratified    epithelium 

(vide  infra}. 


C  (a)  Lining  the  mucous  membrane 
of  the  alimentary  tract — stom- 
ach, small  intestines,  large  in- 
testines, gall-bladder. 

(b)  Lining  the  ducts  of  all  secret- 
ing glands — liver,  pancreas,  sali- 
vary,   lacrimal,    and    mammary 
glands,  testicle,  prostate,  kidney, 
etc. 

(c)  The  deepest  layer  of  cells  in 
stratified  epithelium  is  composed 
of  columnar-shaped  cells,  which, 
however,  differ  in  structure  from 
the  true  columnar  type. 


C  (A)  Plain 


(B)  Modified 
(1)  Ciliated 


(2)  Pyramidal 
or  'glandular' 


(3)  Goblet* 


(a)  Lining   the   uterus    and   ovi- 
ducts. 

(b)  Lining  portions  of  the  ventri- 
cles   of   the   brain    and    central 
spinal  canal  of  the  embryo  and 
infant.     (In  later  life  these  cells 
lose  their  cilia.) 

The  secreting  cells  of  all  tubular 
glands — kidney,  pancreas,  sali- 
vary glands,  intestinal  glands, 
etc. 

(a)  Respiratory     t  r  a  c  t — n  a  s  a  1, 
pharyngeal,  tracheal,   and  bron- 
chial mucous  membranes. 

(b)  Alimentary        tract — stomach, 
small  and  large  intestines. 


*  Cells   whose   protoplasm   has   been    converted    into    mucinogen.      They   may 
be   considered   unicellular,   inucus-secreting   glands. 


EPITHELIAL  TISSUES 


2.  Columnar. 


(4)  Neuro-epi- 
thelium. 


•  (a)  Eye — the   rod   and   cone   cells 
of  the  retina. 

(b)  Ear — in  the  cristse  and  mac- 
ulae of  the  labyrinth  and  in  Cor- 
ti's  organ. 

(c)  Nose — in  the  olfactory  mucous 
membrane  (true  neuron). 

(d)  Tongue — in  the  taste  buds. 


1.  Squamous. 


IT.     COMPLEX    (STKATIFIED)    EPITHELIA— those   whose   cells 
form  several  superimposed  layers. 


Forms  the  epidermis  of  the  skin, 
and  covers  the  free  surface  of 
those  mucous  membranes  which 
clothe  all  orifices  in  direct  con- 
nection therewith — viz.,  the  con- 
junctiva and  cornea;  the  exter- 
nal auditory  canal;  part  of  the 
nasal  mucous  membrane;  mouth, 
pharynx,  and  esophagus;  epi- 
glottis and  vocal  cords;  anus,  as 
high  as  the  internal  sphincter; 
vagina  and  external  portion  of 
the  urethra. 

(a)  Part  of  ductus  deferens. 

(b)  Respiratory  tract;   nasal  mu- 
cous    membrane     and    passages 
connected  therewith,  tear-ducts, 
auditory      tube,      etc.,      larynx, 
trachea,  and  bronchi. 

Genital  tract;  epididymis  and  vas 
deferens. 


2.  Columnar 
(Pseudo- 
stratified 
columnar). 


3.  Transitional. 


Superficial  cells, 
squamous; 
deeper,  polyhe- 
dral; the  deep- 
est, columnar 
in  shape. 


Superficial    cells, 
columnar  j 
deeper       cells, 
polyhedral      or 
spindle-shaped. 

(a)  Non-ciliated 
(rare) 

(b)  Ciliated. 

Superficial     cells  1 
only    somewhat 
flattened;   next 
deeper  layer, 
pear-sliaped; 
deepest  layers, 
polyhedral. 


Found  only  in  the  urinary  system 
— viz.,  pelvis  of  the  kidney,  ure- 
ter, bladder,  and  first  portion  of 
the  urethra. 


NON-STKATIFIED  EPITHELIA 


I.     NON-STRATIFIED    EPITHELIA 

1.     SIMPLE  SQUAMOUS  EPITHELIUM 
(Pavement  Epithelium) 

This  variety  of  epithelium  comprehends  two  main  groups:  (1)  the 
endotlielia,  lining  the  vascular  system,  and  (2)  the  mesothelia  of  the 
serous  membranes  lining  the  large  internal  closed  cavities — pleura^  peri- 
cardium and  peritoneum.  This  distinction  is 
somewhat  arbitrary  but  nevertheless  useful,  and 
derives  justification  in  that  endothelia  arise  in 
the  first  instance  from  syncytial  mesoderm  (mes- 
enchyme)  and  mesothelium  from  epithelial  meso- 
derm. 

But  according  to  Bremer  (Amer.  Jour.  Anat., 
16,  4,  1914),  at  least  some  of  the  earliest  blood- 
vessels in  man  also  arise  from  true  mesothelial 
cells.  Mesothelium  lines  the  extra-embryonic 
body  cavity  and  is  reflected  over  the  yolk-sac  and 
body-stalk.  In  the  latter  location  Bremer  de- 
scribes ingrowths  of  mesothelium  into  the  mesen- 
chyme,  from  which  endothelium  and  blood-cells 
develop. 

This  classification  should  include  also  another 
group  of  closed  cavities,  namely,  the  tendon 
sheaths,  bursas,  joint  or  synovial  cavities,  cham- 
bers of  the  eye,  and  the  scales  tympani  and  vesti- 
buli  of  the  internal  ear.  These  cavities  arise  as 
splits,  or  by  the  union  of  isolated  spaces,  in  the 

mesenchyma,  the  mesenchymal  lining  cells  taking   -pIG  41 SEMIDIAGRAM- 

onepithelioid  characters  and  arranging  themselves  MATIC  ILLUSTRATION 
in  the  form  of  a  membrane.  In  their  method  of  OF  ENDOTHELIUM  LIN- 
,  .  ,.  ,,  ,,  ING  A  LARGE  AR- 

derivation  these  cells  resemble  more  closely  the       TERY 

earliest  endothelial  anlages.     The  most  satisfac- 
tory disposition  of  this  group  of  epithelia  seems  to  be  to  classify  them 
as  'false'  or  'meseiichymal'  epithelia,  as  proposed  by  F.  T.  Lewis. 

Such  epithelia  have  been  experimentally  produced  by  the  introduc- 
tion of  small  sheets  of  celloidin  and  masses  of  paraffin  into  the  subcuta- 


38  EPITHELIAL  TISSUES 

neous  tissue  and  cornea  respectively,  of  laboratory  animals :  the  connective 
tissue  cells  became  changed  into  large  flat  cells,  disposed  in  the  manner 
of  a  mesothelium.  These  results  suggest  the  conclusion  that  the  meso- 
thelial  cells  of  pleura,  pericardium  and  peritoneum  may  be  regenerated 
in  the  event  of  destruction  from  exposed  connective  tissue  cells  of  the 
subepithelial  stroma  (W.  C.  Clarice,  Anat.  Eec.,  8,  2,  1914). 

The  individual  squamous  cells  are  flat  plates  bulging  at  the  center 
where  the  oval  nucleus  is  located,  with  serrated  borders.    In  surface  view 


FIG.  42. — MESOTHELIUM  (surface  view),  FROM  THE  MESENTERY  OF  A  RAT. 
Silver  nitrate  and  hematein.     X  550. 

the  endothelial  cell  is  oblong,  the  long  axis  parallel  with  the  long  axis  of 
the  vessel  (Fig.  41),  while  the  mesothelial  cell  is  polygonal  in  outline 
(Fig.  42).  In  sections  through  the  nucleus,  these  cells  in  side  view 
present  a  flat  spindle-shaped  appearance. 

Mesothelia  exhibit  small  intercellular  spaces,  the  stigmata.  They 
have  been  regarded  as  openings  between  the  body  cavities  and  lymph 
spaces  and  vessels;  but  are  more  probably  transient  structures,  perhaps 
artifacts.  Abdominal  mesothelia  of  lower  forms,  e.g.,  frog,  contain  also 
permanent  openings,  or  stomata,  surrounded  by  specialized  guard  cells. 

The  mesenchymal  epithelial  cells  of  synovial  membranes  vary  greatly 
in  shape  according  to  the  degree  of  pressure  to  which  they  are  subjected. 
They  may  thus  be  of  the  cuboidal  or  the  squamous  type ;  and  they  may 
even  become  pressed  apart  so  as  to  expose  the  underlying  connective 
tissue.  (Compare  Figs.  44  and  240.) 


NON  STRATIFIED  EPITHELIA 


3!) 


2.     SIMPLE  COLIMXAI;  KI-ITHELIUM 

(a)      J'lain 

This  type  of  epithelium  consists  cf  columnar  or  cylindrical  elements 
(Fig.  30),  in  transverse  section  presenting  polygonal,  frequently  hex- 
agonal, outlines  (Fig.  40).  It 
may  be  tall,  medium  or  low 
columnar  epithelium,  depend- 
ing upon  the  height  of  the  in- 
dividual cell  of  the  particular 
membrane.  The  lower  types 
may  be  designated  cuboidal 
epithclia  (Fig.  43).  The  phe- 
nomenon of  polarity  is  partic- 


ELIUM FROM  THE 
s  OF  THE  RABBIT. 


FIG.  43.—  C 

RETE  TES 

a,  epithelium;  b,  connective  tissue.    Hema- 
tein  and  eosin.     X  550. 


ularly  well  exhibited  by  a  tall 
columnar  cell,  a  condition  inhering 


FlG.     44.— TIP    OF    A     VlLLUS    OF    THE 

SYNOVIAL    MEMBRANE    FROM    THE 
KNEE-JOINT  OF  AN  OLD  MAN. 
The    core    contains    capillaries    em- 
bedded in  a  compact,  delicately  fibrillar 
stroma.      A   distinct   basement    mem- 
brane appears  in  certain  regions.    The 
epithelium  is  of  the  low  columnar  or 
cuboidal  type. 


in  a  structural  and  functional  differ- 
entiation between  the  attached,  or 
proximal,  and  the  free,  or  distal,  end 
of  the  cell,  dependent  in  a  final  an- 
alysis in  larger  measure  upon  dis- 
tance from  source  of  the  nutritive 
and  oxygenative  stream  in  the  blood. 
The  nucleus  is  generally  located 
nearer  the  proximal  end;  this  end, 
moreover,  tapers  to  a  point  and  is 
occasionally  bifid;  and  it  contains 
the  presecretion  (ergastoplasm,  pro- 
xy mogen,  etc.)  granules,  rodlets  and 
fibrils  in  secreting  epithelia  (Fig. 
35  )  .  The  distal  border  is  frequently 
striated  (cutieular  margin,  striated 
border,  Fig.  38,  b),  an  appearance 
due  to  the  presence  of  minute  canals, 
or  more  frequently,  short  pseudo- 
podia,  mediating  absorption  or  the 
elimination  of  secretion.  Striated 
borders  are  particularly  prominent 
in  the  columnar  cells  of  the  intes- 
tine. In  the  secreting  cells  of  tiro 


40 


EPITHELIAL  TISSUES 


kidney  the  marginal  processes  are  more  prominent  and  divergent,  forming 
'brush  borders.'  Where  the  cell  membrane  becomes  greatly  thickened  on 
the  free  surface  of  a  columnar  cell,  it  is  termed  a  crusta.  Also,  in  neuro- 
epithelial  cells,  the  free  border  mediates  reception,  the  attached  pole 
transmission,  of  stimuli. 


(b)     Modified  'Columnar  Epithelium 

(1)  Ciliated  Epithelium. — Here  the   columnar   cells   carry  upon 
their  free  surface  a  group  of  delicate  hairlike  processes  called  cilia,  or  a 
single  flagellum   (flagellate  cells  of  lower  forms),  which  during  life  are 

capable  of  a  rapid  vibratory  or  undu- 
latory  motion,  a  further  expression  of 
cell  polarity.  The  direction  of  this 
ciliary  motion  is  constant  and  is  such 
as  to  produce  a  definite  current  within 
the  fluids  which  bathe  the  surface  of 
these  cells  whose  direction  is  invariably 
from  within  toward  the  external  surface 
of  the  body.  In  the  human  body  the 
cilia  occur  almost  exclusively  upon  the 
free  extremities  of  columnar  cells 
(Figs.  45,  51  and  52).  In  some  of  the 
lower  animals,  as  for  example  in  the 
mouth  of  the  frog,  cilia  are  found  also 
upon  polyhedral  and  pear-shaped  cells. 
In  simplest  form  cilia  are  pseudopod- 
like  extensions  of  the  cytoplasm  of  the 
cell  body,  and  may  be  regarded  as  modifications  of  its  exoplasm. 

The  ciliated  border  is  separated  from  the  protoplasm  of  the  cell  body 
by  a  fine  chromatic  line,  which  on  higher  magnification  resolves  into  a 
number  of  knob4ike  segments,  the  basal  granules  (Fig.  22,  Chap.  I).  The 
cytoplasm  and  nucleus  of  ciliated  epithelium,  except  for  the  peculiarities 
dependent  upon  the  formation  of  cilia,  is  similar  to  that  of  the  simple 
non-ciliated  columnar  cells.  Their  cytoplasm  as  in  other  types,  may 
contain  vacuoles,  pigment  granules,  metaplasm,  and  even  secretory 
granules,  e.g.,  epididymis. 

(2)  Glandular  Epithelium. — This  type  derives  its  name  from  the 
fact  of  the  predominance  of  the  glandular  function.     This  condition  is 


FIG.  45. — COLUMNAR  CILIATED  EPI- 
THELIUM FROM  THE  EPIDIDYMIS 
OF  A  RABBIT. 

a,  epithelium;  6,  connective  tissue; 
c,  cilia.  A  leukocyte  is  seen  between 
the  bases  of  the  columnar  cells. 
Hematein  and  eosin.  X  550. 


NON-STRATIFIED  EPITHELIA  41 

structurally  expressed  in  segregation  of  the  presecretion  bodies  (gran- 
ules, rods,  threads)  in  the  basal  end  of  the  cell,  and  of  the  secretion 
products  (granules,  spherules,  and  mucous  or  serous  fluid)  in  the  distal 
end  (Fig.  35).  Morphologically  it  represents  simply  a  modified  colum- 
nar cell,  its  pyramidal  shape  resulting  from  mechanical  factors  due  to 
its  disposition  in  saccular  or  spherical  acini,  the  periphery  of  the  cen- 
tral lumen  of  which  is  much  less  than  the  periphery  of  the  acinus, 
necessitating  the  modification,  in  shape  of  the  individual  cells  (Fig.  46). 
The  cells  of  glandular  epithelium  usually  lack  cuticular  borders.  Pyram- 
idal or  glandular  epithelium  is  found  in  tubules  of  the  kidney,  salivary 
glands,  the  pancreas,  in  the  -secreting 
glands  of  the  gastric  and  intestinal 
mucous  membrane,  in  the  mucous 
glands  of  the  esophagus,  pharynx, 
bronchial  tubes  and  oral  and  nasal 
cavities,  and  in  the  secreting  glands  of 
the  skin. 

(3)     Goblet  Cell  Epithelium.— A 
further  important  and  very  widespread 
modification  of  columnar  cells  in  epi-    FIG.  46. — A  GROUP  OF  CELLS  FROM 
thelia    concerns    the    elaboration    and        A  TRANSECTION  OF  AN  Acmus  OF 
, .  .   .  THE  HUMAN  PANCREAS;  GLAND  u- 

storage  of  mucous  secretion,  giving  to        ^  EPITHELIUM. 

the  loaded  cells  a  goblet  form  (Figs.  47        Hematein  and  eosin.     X  550. 
and  48) .    Goblet  cells  may  occur  among 

either  the  plain  or  ciliated  columnar  cells.  They  are  most  abundant  in 
the  intestinal  tract  but  are  also  to  be  found  in  the  stomach,  bronchial 
tubes,  trachea,  nasal  mucous  membrane,  and  in  the  ducts  and  tubules  of 
mucus  secreting  glands.  In  such  epithelial  membranes  certain  columnar 
cells,  if  not  indeed  all  of  these  cells,  are  destined  to  secrete  mucus.  The 
cytoplasm  of  such  cells  is  converted  into  a  glairy  mass  of  a  peculiar  vitre- 
ous appearance,  which  occupies  an  increasing  proportion  of  the  free  ex- 
tremity of  the  cell.  This  'mucinogen/  when  acted  upon  by  alcohol,  is 
precipitated  within  the  cell,  and  then  forms  fine  basophilic  fibrils  or  gran- 
ules which  stain  deeply  with  the  muchematein  and  mucicarmin  solutions 
of  P.  Mayer.  At  the  base  of  the  goblet  cell,  its  nucleus  is  embedded  in  a 
minute  mass  of  unaltered  granular  cytoplasm. 

The  accumulation  of  mucus  (mucinogen)  within  the  cytoplasm  ex- 
pands the  cell,  finally  ruptures  its  wall  in  the  direction  of  least  resistance, 
and  thus  permits  its  mucous  content  to  exude  upon  the  free  surface, 
leaving  behind  the  small  granular  protoplasmic  cell  remnant  attached  to 


4  o 


EPITHELIAL  TISSUES 


the  basement  membrane.  The  further  history  of  these  cell  remnants  is 
somewhat  doubtful.  They  are  possibly  resorbed  or  removed,  and  finally 
replaced  through  mitotic  division  of  adjacent  cells.  There  is,  however, 
some  evidence  to  show  that  after  function  they  are  still  capable  of  further 


FIG.  47. — GOBLET  CELLS   AS   SEEN  IN 
A  TRANSECTION  OF  A  CRYPT  OF  THE 
LARGE  INTESTINE  OF  MAN. 
Sections  of  five  goblet  cells  are  seen 

among  the   columnar    cells  which    line 

the   tubule.     Muchematein   and   eosin. 

X550. 


FIG.  48. — DIAGRAM  SHOWING  THE  AR- 
RANGEMENT OF  THE  COLUMNAR  AND 
GOBLET  CELLS  OF  THE  PRECEDING 
FIGURE. 

The  goblet  cells  are  represented  as 
being  empty;  their  unaltered  basal  por- 
tions containing  the  nucleus  are  dis- 
tinctly seen. 


growth,  whereby  they  may  regain  their  original  form  and  become  again 
able  to  pass  through  the  same  stages  of  secretory  activity. 

(4)  Neuro-epithelium. — The  cells  of  neuro-epithelium  are  colum- 
nar elements  specially  differentiated  to  form  nerve  end-organs.  They 
are  usually  elongated  cells  having  a  bulging  nucleated  center,  their  free 
extremity  either  projecting  beyond  the  epithelial  surface  as  a  bundle  of 
fine  cilia  or  as  a  slender  non-ciliated  process  which  terminates  within  a 
pore-like  opening  directly  connected  with  the  free  surface.  Their  at- 
tached extremity,  tapering  to  a  fine  process,  is  in  relation  with  the 
terminal  arborization  of  the  axis  cylinder  of  a  nerve  fiber.  Neuro-epithe- 
lium  is  found  only  in  the  several  organs  of  special  sense,  and  will  be  more 
fully  described  as  a  part  of  these  several  organs.  (See  chapters  of  the 
Eye,  the  Ear,  the  Olfactory  Organ,  the  Tongue,  and  on  the  ISTerve  End- 
Organs.) 


STKATIFIED  EPITHELIUM  43 

H.     STRATIFIED    EPITHELIUM 

1.     STRATIFIED  SQUAMOUS  EPITHELIUM 

This  variety  of  epithelium  occurs  as  a  membrane  of  varying  thickness 
but  always  comprising  several  cell  layers.  A  straight  line  perpendicular 
to  its  free  surface  would  penetrate  from  five  to  thirty  or  more  epithelial 
cells.  But  while  there  is  a  wide  diversity  in  the  thickness  of  the  epithelial 
layers,  the  character  of  the  cells  at  any  given  level  is  very  nearly  con- 

^^          ^      .  ®       &          ^ 

\    £      ~     *V:      &®*    *%> 
a,  <SS>          a,          <&> 

S%-e  •<»        ©      *   ® 

}®.      @ ">  '^ -»:..•! 

L*  ®  .  -  9o  9  '®      &      ® 
©<©  &  o  © 


FIG.  49. — STRATIFIED  EPITHELIUM  FROM  THE  HUMAN  ESOPHAGUS. 
a,  basement  membrane;  6,  connective  tissue.    Hematein  and  eosin.     X  410. 

stant.  Thus  the  deeper  cells,  those  nearest  the  basement  membrane,  are 
nucleated,  of  soft  consistence  and  may  contain  mitotic  figures,  indicating 
that  it  is  at  this  level  that  cell  reproduction  is  most  active.  Toward  the 
surface  of  the  membrane  the  cells  become  progressively  of  firmer  con- 
sistence, so  that  the  most  superficial  ones  present  a  horny  appearance  as 
a  result  of  the  gradual  keratization  of  the  cytoplasm  during  the  progress 


44  EPITHELIAL  TISSUES 

of  the  cell  toward  the  surface.  The  keratization  is  apparently  dependent 
upon  surrounding  physical  conditions,  for  it  is  much  more  marked  in 
the  skin,  which  from  constant  and  rapid  evaporation  is  comparatively 
dry,  than  in  the  mouth,  esophagus,  or  conjunctiva,  where  the  epithelium  is 
constantly  moistened  by  glandular  secretions;  the  margins  of  the  lips, 
eyelids,  etc.,  present  an  intermediate  state  of  keratization. 

With  these  chemical  changes  in  the  composition  of  the  cytoplasm 
there  are  corresponding  changes  in  its  nucleus.  In  the  deeper  cells,  the 
nucleus  is  oval  or  spherical  and  highly  chromatic.  Toward  the  surface, 
the  nucleus  becomes  more  and  more  flattened  and  more  and  more  obscured 
by  the  cornification  of  the  cell  protoplasm.  In  the  most  superficial  cells 
it  is  usually  impossible  to  demonstrate  the  nuclei,  except  by  acting  upon 
their  protoplasm  with  strong  reagents  such  as  caustic  alkalies,  soda  or 
potassa. 

But  the  most  characteristic  change  in  the  cells  of  stratified  epithelium 
is  the  progressive  transition  in  shape  undergone  during  their  passage 
from  the  deeper  layers  to  the  free  surface.  Xew  cells,  resulting  from  indi- 
rect division  of  the  cells  in  the  deeper  layers,  are  by  continued  reproduction 
gradually  pushed  toward  the  surface,  whence  they  are  constantly  being 
desquamated  in  small  scaly  masses.  The  pressure  exerted  in  this  process 
tends  to  gradually  flatten  these  cells  so  that  their  vertical  diameter,  that 
perpendicular  to  the  surface,  becomes  progressively  shorter  the  nearer 
they  approach  the  free  surface ;  on  the  other  hand,  their  transverse  diam- 
eter, that  parallel  to  the  surface  of  the  epithelial  membrane,  is  correspond- 
ingly increased.  The  deepest  cells  of  the  stratified  epithelium — those 
which  rest  upon  the  basement  membrane — are  elongated  in  their  vertical 
diameter  and  possess  an  irregularly  columnar  shape.  Their  nuclei  are 
likewise  elongated,  oval  or  elliptical  in  shape.  In  the  skin  of  brunettes 
and  the  dark-skinned  races,  and  in  the  epithelium  of  the  skin  of  the 
scrotum,  perianal  region,  and  areolae  of  the  breasts,  these  cells  contain 
small  granules  of  the  pigment  to  which  the  color  of  the  cuticle  is  largely 
due.  This  columnar  cell  layer  is  then  described  as  the  layer  of  pigment 
epithelium.  Superficial  to  these,  but  still  in  the  deeper  layers,  are  poly- 
hedral cells  with  spherical  nuclei,  which  are  known  as  prickle  cells  be- 
cause of  their  prominent  intercellular  bridges.  Superficial  to  the  prickle 
cells,  the  epithelial  cells  become  progressively  more  flattened,  until  at  the 
surface,  they  are  mere  scales.  This  gradual  transition  from  columnar 
and  polyhedral  cells  below,  to  thin  flat  scales  on  the  surface  is  character- 
istic of  all  stratified  epithelium. 

The  thin  superficial  scales  resemble  very  closely  in  shape  and  appear- 


STRATIFIED  EPITHELIUM 


45 


ance  the  squamous  epithelium  previously  described.  The  deeper  cells  have 
a  finely  granular  cytoplasm  and  distinct  nuclei  except  when  obscured  by 
the  appearance  of  keratin  within  their  protoplasm.  Many  of  these  cells 
contain  coarse  granules  of  eleidin  and  keratoltyalin — substances  chemi- 
cally intermediate  between  the  unaltered  and  keratized  protoplasm. 

As  stated,  the  formation  of  keratin  within  these  cells  is  more  active 
in  those  membranes  which  are  comparatively  dry  from  exposure  to  the 
air.  Consequently,  it  is  most  active  in  the  epidermis  of  the  skin.  If 
stratified  epithelium  is  at  all  times  well  moistened,  as,  for  example,  in  the 


FIG.  50. — EPIDERMIS  OF  THE  SKIN  OF  THE  FINGER  TIP,  SHOWING  EXTREME  KERATIZA- 

TION  OF  THE  EPITHELIUM. 

a,  keratized  epithelium;  6,  Malpighian  or  germinal  layer;  c,  connective  tissue. 
Hematein  and  eosin.     X  50. 

mouth  and  esophagus,  the  formation  of  keratin  is  slight,  and  the  soft 
polyhedral  cells  compose  the  major  portion  of  the  epithelial  membrane 
which  then  has  only  a  thin  superficial  covering  of  flattened  scaly  cells. 
In  the  comparatively  dry  epidermis,  on  the  other  hand,  the  flattened 
horny  cells  frequently  occupy  more  than  half  the  thickness  of  the  epithe- 
lial layer  (Fig.  50) .  In  the  superficial  squamous  cells  of  moist  membranes 
the  nucleus  can  always  be  readily  demonstrated,  even  in  the  keratized 
cells  of  the  extreme  surface.  Cells  of  the  intermediate  layers,  especially 
those  just  above  the  prickle  cell  layer,  frequently  show  nuclei  in  process  of 
amitotic  division.  This  condition  is  presumably  associated  with  an  early 
stage  of  degeneration  dependent  upon  a  scarcity  of  nutriment  due  to 
the  relatively  greater  distance  of  these  cells  from  the  source  of  supply. 


EPITHELIAL  TISSUES 


It  will  assist  in  the  understanding  of  the  structure  and  morphological 
characteristics  of  the  several  layers  of  cells  to  think  of  the  superficial 
a  squamous  cells  in  terms  of  the  innermost 

columnar  cells,  modified  during  the  pas- 
sage; to  the  surface  by  mechanical  (pres- 
sure), physical  (desiccation),  and  chem- 
ical (keratization)  factors. 


.•©e 


PSEUDO-STRATIFIED    COLUMNAR 

EPITHELIUM 


The  superficial  cells  only  of  this  va- 
riety of  epithelium  are  columnar  in 
shape,  and  except  in  one  or  two  unim- 
portant places  are  always  ciliated.  The 
deeper  extremities  of  these  columnar 
cells  taper  to  a  point,  and  extend  all  the 
way  to  the  basement  membrane.  Be- 
tween the  tapering  ends  of  these  cells 
small  spindle-shaped  and  spheroidal  cells 
The  several  varieties 


FlG.  51 . — P  S  E  U  D  O  -  STRATIFIED 
COLUMNAR  CILIATED  EPITHE- 
LIUM FROM  A  BRONCHIAL  TUBE 
OF  MAN. 

a,  a  goblet  cell;  1>,  cilia;  c,  super- 
ficial cytoplasrnic  layer;  d,  deeper 
nucleated  layer,  the  nuclei  of  the 
columnar  cells  are  somewhat  more 
deeply  stained  than  those  of  the 
basal  cells;  e,  basement  mem- 
brane;/, connective  tissue.  Hema- 
tein  and  eosin.  X  550. 

are  closely  packed. 

of  cells  thus  appear  to  be  superimposed,  though 
all  actually  rest  upon  the  basement  membrane. 
The  'superficial'  cells  of  this  variety  extend 
throughout  the  entire  thickness  of  the  mem- 
brane. Hence  this  form  of  epithelium  may  in 
one  sense  be  called  'simple'  rather  than  'strat- 
ified.' The  distribution  of  this  variety  of  the 
epithelium  is  practically  identical  with  that  of 
ciliated  cells.  The  deeper  extremities  of  the 
columnar  cells  are  occasionally  bifid  or  even 
somewhat  varicose  in  order  the  more  closely  to 
fit  between  the  spindle-shaped  and  spheroidal 
cells  of  the  deeper  portion.  The  nucleus  of  these 
latter  cells  is  usually  situated  a  little  below  the 
middle  of  the  columnar  cell,  so  that  all  the  nuclei 
of  the  epithelial  membrane  lie  within  its  deeper 
half,  thus  giving  to  tthis  portion  a  more  deeply 
chromatic  appearance  when  observed  in  stained  sections  under  low  mag- 
nification. The  superficial  half  of  the  epithelial  layer  contains  only 


FIG.  52.  —  DIAGRAM 
SHOWING  THE  MAN- 
NER IN  WHICH  ALL 
THE  EPITHELIAL 
CELLS  OF  PSEUDO- 
STRATIFIED  CILIATED 
EPITHELIUM  REACH 
THE  BASEMENT  MEM- 
BRANE. 

Letters  as  in  the  pre- 
ceding figure. 


/  STRATIFIED  EPITHELIUM  47 

the  cytoplasmic  portion  of  the  columnar  cells  with  their  ciliated  bor- 
ders. 

This  type  of  epithelium  is  frequently  designated  simply  'stratified 
columnar';  and  in  fact  in  certain  instances  under  conditions  of  further 
modification  involving  a  separation  of  the  taller  cells  from  the  basement 
membrane,  it  passes,  over  more  or  less  extensive  areas  in  the  respiratory 
and  male  genital  tracts,  into  actual  stratified  columnar  epithelium. 
Toward  the  proximal  end  of  the  male  urethra  the  epithelium  is  of  the 
true  stratified  columnar  (non-ciliated)  type. 

3.     TRANSITIONAL  EPITHELIUM 

This  variety  resembles  somewhat  stratified  squamous  epithelium  in 
that  it  is  composed  of  several  cell  layers,  the  deeper  cells  of  which  are 
mqre  nearly  polyhedral  but  are  somewhat  flattened  upon  the  free  sur- 
face, but  differs  in  having  a  smaller  number  of  cell  layers — in  which 
respect  it  is  'transitional* 

between  simple  and  strat-  ^  ^^     «.  ^^ 

ified   squamous    epitheli-          A  £  0&  t£y^ 

u  m — and  in  the  charac-       £  ^  £  /& 

ter     of     the     superficial  ®  fy  A        %    0 

cells.      Transitional   epi-        0  ^  ^ 

(helium    is    not    usually       ^        At        £  £|      _      A       £      A 
more  than  from  three  to  *  %  <j& 

ten  cells  deep,  four  to  six  %        %     flfc       C'  \|>    %         ^      $jh 

being    the     rule.       The      ^^      •       •SV  %^  fc  •  A 
number  of  cell  layers  and  ^  ^  ^  ^ 

the     consequent     actual       «n_  ^      ®  ^  ^ 

thickness     of     epithelial  «•  •&       ^^k^^^    " 

membranes  is  to  a  cer- 
tain    extent     dependent      FlG"  ^.-TRANSITIONAL  EPITHELIUM  FROM  A  THAN- 

SECTION    OF   THE    IjRETER    OF   AN    INFANT. 

upon  their  state  of  ten-  ...   ,.        ,  t.     A.  A  .        , 

.  r,  epithelium;  b,  connective  tissue.    Hematem  and 

sion  during  life;  thus  the      cooin.    X  550. 

transitional  epithelium  of 

the  urinary  bladder  is  much  thicker  when  the  organ  is  collapsed  than  dur- 
ing distension. 

The  deepest  "cells  are  polyhedral,  and  these  form  the  greater  portion 
of  the  membrane.  Only  the  more  superficial  layers  differ  therefrom. 
Those  polyhedral  cells  which  lie  in  the  midregion  of  the  epithelial  layer 
s  a  peculiar  flask  or  pear  shape,  with  well-rounded  bodies  and  a 


48 


EPITHELIAL  TISSUES 


broad  tapering  process  which  is  embedded  between  the  adjacent  cells  of 
the  deeper  layers.  The  rounded  extremities  of  the  pear-shaped  cells  fit 
into  peculiar  indentations  in  the  deeper  surface  of  the  superficial  layer 
of  epithelial  cells,  producing  peculiar  concave  facets,  which  are  specially 
characteristic  of  the  detached  superficial  cells  of  transitional  epithelium. 
The  superficial  cells,  while  somewhat  flattened,  usually  have  a  thick- 
ness equal  to  one-sixth  to  one-third  their  transverse  diameter.  In  this 
respect  they  differ  markedly  from  the  superficial  scaly  cells  of  stratified 
squamous  epithelium  and  are  easily  distinguished  therefrom,  even  in  the 


FIG.  54. — ISOLATED  CELLS  WHICH  MAY  APPEAR  IN  HUMAN  URINE. 
A,  from  the  vagina  of  a  woman  (stratified  squamous  epithelium);  B,  from  the 
ureter  of  a  child  (transitional  epithelium);  a,  cells  from  the  deep  layers;  6,  superficial 
cell.    Moderately  magnified. 

isolated  condition  in  which  they  are  frequently  found  in  the  urine. 
The  concave  facets  on  their  under  surface,  as  well  as  the  peculiar  pyri- 
form  shape  and  small  size  of  the  deeper  cells,  are  sufficient  to  distinguish 
the  transitional  cells  from  those  of  stratified  epithelium. 

There  is  little,  if  any,  formation  of  keratin  in  transitional  epithelium. 
This  is  possibly  explained  by  the  fact  that,  as  it  occurs  only  in  the 
urinary  system,  this  form  of  epithelium  is  always  well  moistened.  Differ- 
entiation of  this  variety  of  epithelial  tissue,  though  neglected  by  some 
authors,  becomes  most  important  in  the  clinical  examination  of  urine 
where  it  is  necessary  to  determine  the  origin  of  individual  cells.  Transi- 
tional cells  from  the  bladder  are  easily  distinguished  from  the  stratified 
squamous  cells  of  th*e  vagina,  urethra,  or  epidermis. 


CHAPTER   III 
CONNECTIVE   TISSUE— CARTILAGE— BONE 


CONNECTIVE  TISSUE 

General  Statements.— While  in  the  epithelial  tissues  the  cells  are 
developed  chiefly  at  the  expense  of  the  intercellular  elements,  in  the 
connective  or  supporting  tissues  the  conditions  are  the  reverse.  The 
intercellular  elements  are  here  developed  out  of  all  proportion  to  the 
connective  tissue  cells.  The  cells  of  these  tissues  therefore  are  scanty, 
the  ground  substance  considerable,  and  within  the  latter  a  new  element, 
the  connective  tissue  fiber,  makes  its  appearance.  The  fibers  are  of  three 


FIG.  55. — EMBRYONAL  CONNECTIVE 

TISSUE,  EARLY  STAGE. 
Highly  magnified.  (After  Mall.) 


FIG.  56. — EMBRYONAL  CONNECTIVE  TIS- 
SUE AT  A  LATER  STAGE  THAN  Is  REP- 
RESENTED IN  FIG.  55.  (After  Mall.) 


varieties:  wliite  or  collagenous  fibers,  elastic  fibers,  and  reticulum.  In 
any  given  location  either  of  these  varieties  may  predominate  to  such  an 
extent  as  to  determine  the  character  of  the  mature  tissue,  while  in  the 
immature  forms  of  connective  tissue  it  is  the  cellular  elements  which 
attain  the  greatest  prominence. 

The  minute  structure  of  connective  tissue  is  subject  to  great  and 
important  changes  during  its  development.  Beginning  as  it  does  with 
the  primitive  mesoderm,  connective  tissue  is  originally  a  cellular  struc- 
ture. The  cells  of  primitive  connective  tissue,  the  fibroblasts,  not  only 
increase  in  number  by  cell  division  but  also  secrete  an  intercellular 
ground  substance  of  semifluid  consistence.  The  fibroblasts  fuse  with  each 
5  49 


50 


CONNECTIVE  TISSUE— CARTILAGE— BONE 


other  and  finally  form  a  syncytial  tissue,  the  mesenclnjma,  in  which 
there  promptly  occurs  a  differentiation  of  the  cytoplasm  with  the  forma- 
tion of  an  endoplasm  and  an  exoplasm;  and  within  the  latter  tin.-  fine 
fibrils  soon  make  their  appearance,  according  to  Meves,  hv  processes 
of  fusion  and  chemical  alteration  of  mitochondria  (chundrioronta ). 
This  process  continues,  new  ground  substance  and  fibers  being  uon- 


\Vz     Kolf     Kl    Elf      Plz 


FIG.  57. — SUBCUTANEOUS  AREOLAR  CONNECTIVE  TISSUE  OF  GUINEA  PIG. 
(Maximow.) 

Elf,  elastic  fiber;  Kolf,  collagenous  (white)  fiber  bundles;  Fb,  fibroblast  (lamelhr 
cell);  Mz,  mast  cell;  Wz,  resting  wandering  cell  (clasmatocyte);  Plz,  plasma  cell;  Kl, 
clasmatocyte  ('macrophage');  Eos,  eosinophil.  X  1750. 

stantly  formed  at  the  expense  of  the  endoplasm,  until  finally  the  remnant 
of  the  latter  again  forms  isolated  cells.  The  culmination  of  these  changes 
results  in  the  mature  fibrillar  connective  tissue  in  which  the  cells  are 
shrunken  and  scarce,  though  still  apparently  capable  of  assuming  renewed 
activity  on  demand  of  altered  conditions.  The  definitive  fibrils  result  in 
part  from  a  longitudinal  splitting  of  the  coarser  primitive  fibers,  collage- 
nous  (Mall),  elastic  and  reticular. 

Embryonic  connective  tissue  is  therefore  typically  cellular  as  com- 
pared with  the  mature  type;  its  ground  substance  is  abundant  but  tlio 
fibers,  whose  development  is  as  yet  incomplete,  are  scanty.  Such  embvv- 


CONNECTIVE  TISSUE 


51 


onic  connective  tissue  is  found  not  only  in  the  fetus  but  also  in  early  child- 
hood and  in  the  adult,  especially  during  regeneration  of  destroyed  areas 
of  connective  tissue,  and  in  other  more  or  less  pathological  conditions. 


FIG.  58.  — PLASMA 
CELLS  OF  CONNEC- 
TIVE TISSUE  FROM 
THE  HUMAN  BREAST. 
Hematein  and  eosin. 
X  750. 


CONNECTIVE  TISSUE  CELLS 

Connective  tissue  cells  not  only  vary  in  number  as  they  approach  ma- 
turity, but  in  their  structure  and  appearance  as  well.  The  cells  of  em- 
bryonic connective  tissue  are  comparatively  large,  are  frequently  stellate 
from  the  presence  of  numerous  interlacing  and 
sometimes  anastomosing  branches,  and  their  cyto- 
plasm has  a  typical  reticular  or  granular  appear- 
ance. In  the  later  stages  of  their  development 
ameboid  motion  has  been  observed  in  such  cells, 
and  within  the  limits  of  the  tissue  in  which  they 
are  developed,  they  are  presumably  endowed  with 
the  power  of  locomotion. 

In  the  neighborhood  of  developing  blood-ves- 
sels plasma  cells  of  large  size  and  irregular  shape 
are  frequently  s*een.  The  cytoplasm  of  these  cells 

is  of  considerable  volume,  is  finely  granular,  stains  readily  in  most  dyes, 
especially  the  basic  varieties,  and  is  prolonged  into  broad  protoplasmic 
branches  of  considerable  length.    Both  in  the  cell  body  and  in  the  proc- 
esses vacuoles  are  so  numerous  as  to  give  the  cell  a  typically  reticular 
appearance,  a  peculiarity  which  is  emphasized 
^  by  the  removal  of  the  contents  of  the  vacuoles, 

^  ^  ^^  as  frequently  happens  in  the  preparation  of 

microscopical  specimens.  Plasma  cells  are 
found  in  considerable  numbers  in  the  mucous 
membrane  of  the  intestinal  tract  and  in  the 
subcutaneous  tissue,  where  they  are  frequently 
of  spheroidal  form. 

In  the  denser  forms  of  mature  connective 
tissue,  where  the  cells  are  apparently  subjected 

to  more  or  less  compression  between  the  firm  bundles  of  fibers,  the  con- 
nective tissue  cells  lose  their  typical  embryonal  stellate  form  and  become 
somewhat  fusiform;  they  are  then  known  as  the  spindle  cells  of  connec- 
tive tissue.  Such  cells  occur  in  great  abundance  in  the  stroma  of  the 
ovary  and  the  mucosa  of  the  uterus  and  oviduct. 

In  the  mature  tissue  of  the  adult  many  of  the  cells  become  more  or 


FIG.    59. — SPINDLE-SHAPED 
CONNECTIVE    TISSUE 
CELLS  FROM  THE  STROMA 
OF  THE  HUMAN  OVARY. 
Hematein      and 
X  550. 


eosm. 


CONNECTIVE  TISSUE— CABTILAGE— BONE 


FlG.  60. — PlGMENTED  CELLS  FROM  THE 

CHOROID  COAT  OF  THE  Ox's  EYE. 

Unstained;  hence,  only  the  pigment 
granules  appear  in  the  figure.  1,  gran- 
ules contained  within  the  cytoplasm ;  2, 
free  granules  which  have  escaped  from 
cells  injured  during  the  process  of  teas- 
ing; 3,  the  non-pigment  ed  nuclei. 


less  flattened  and  are  often  closely  applied  to,  or  even  wrapped  around, 
the  fiber  bundles.  These  lamellar  cells  have  a  small  nucleus,  a  consider- 
able rim  of  cytoplasm,  which  fre- 
quently has  a  shrunken  appearance, 
and  sometimes  a  few  short  cytoplas- 
mic  processes.  The  branching  stel- 

.-™™r  -  .        late  forms,  however,  are  characteris- 

y  *  '^jfeg&  .     tic  of  the  younger  connective  tissues. 

ffi$f3  In  certain  locations  a  deposit  of 

pigment  granules  occurs  within  the 
connective  tissue   cells.      Such  pig- 

""^BterfS^".    '         •    .'*•..!     ment  .cells  are  usually  found  where 
B\.  protection  against  light  seems  desir- 

able, and  are  most  abundant  in  the 
choroid  coat   and  iris   of   the   eye. 
The  pigment  granules  are  entirely 
confined    to   the    cytoplasm   of   the 
cell ;  the  nucleus  is  never  invaded  by 
the  deposit.     These  granules  belong 
to  the  melanin  series  of  pigments. 
The  cytoplasm  of  certain  cells  found  in  connective  tissue  contains 
coarse   basophil  granules,  which   stain  with   dahlia  and   similar   basic 
dyes.     This  type  is  known  as  lasophil  granule  cells, 
or  mast  cells  (Mastzellen  of  the  German  authors). 
The  granules  of  other  granulocytes  are  readily  stained 
with  acid  dyes,  such  as  eosin  (eosinopliil,  acidopliil 
or  oxyphil  granulocytes).    According  to  the  observa- 
tions of  H.   B.   Shaw    (Jour.   Anat.  and  Physiol., 
1901),  certain  of  the  granule  cells  abound  in  those 
locations  where  fat  is  deposited,  and  have  a  special 
relation  to  the  development  of  the  fat  cells  of  adipose 
tissue.    These  granulocytes  of  fibro-elastic  connective 
tissue  are  apparently  identical  with  those  of  the  blood. 
Lymphocytes  and  phagocytic  leukocytes  are  also  pres- 
ent in  connective  tissue. 

It  is  a  disputed  point  whether  the  granulocytes  of 
connective    tissue    differentiate   from    fibroblasts    or 
from  lymphocytes ;  the  weight  of  evidence  seems  to  incline  to  the  latter 
position.     Plasma  cells  seem  more  probably  altered  fibroblasts  but  have 
also  been  regarded  by  some  as  lymphocyte  derivatives.     The  so-called 


FIG.  61. — GRANULE 
CELLS  FROM  THE 
FIBROUS  CON- 
NECTIVE TISSUE 
OF  THE  HUMAN 
MAMMARY  GLAND. 

A,  a  basophile 
cell;  B,  an  eosino- 
phile  cell.  Hema- 
tein  and  eosin.  X 
750. 


CONNECTIVE  TISSUE  53 

testing-wandering'  cells,  or  'clasmatocytes,'  are  perhaps  to  be  regarded 
as  varieties  of  basophilic  granulocytes  characterized  principally  by  the 
presence  of  irregular  protoplasmic  processes.  According  to  Kite  (Jour. 
Infec.  Dis.,  15,  2,  1914)  the  'clasmatocytes'  described  for  the  frog  by 
Ranvier  in  1891  are  lymphocytes  which  have  protruded  pseudopods. 
Evans  classifies  them  with  the  'macrophages'  of  Metschnikoff. 

TYPES  OF  CONNECTIVE  TISSUE 

The  proportions  and  character  of  the  cells  and  fibers  present  in 
any  given  connective  tissue,  to  a  certain  extent  determine  its  character. 
If  the  collagenous  fibers  of  connective  tissue  are  closely  packed  in  dense 
parallel  bundles,  the  elastic  fibers  being  comparatively  insignificant  in 
number,  the  type  of  connective  tissue  may  then  be  said  to  be  dense 
fibrous  or  white  fibrous  tissue. 

In  elastic  tissue  on  the  other  hand,  the  yellow  elastic  fibers  are  highly 
developed,  the  white  fibers  forming  only  insignificant  and  very  delicate 
sheaths  which  inclose  the  coarser  elastic  fibers. 

Again,  it  is  the  variety  of  delicate  connective  tissue  fiber  known  as 
reticulum  which  preponderates  in  reticular  tissue,  and  if  the  meshes  of 
this  reticular  network  become  infiltrated  by  lymphocytes,  which  then  mul- 
tiply by  division  until  they  exceed  the  other  tissue  elements,  the  connective 
tissue  is  then  said  to  be  of  the  lymphoid  or  adenoid  variety.  Large  num- 
bers of  the  fixed  cells  of  areolar  connective  tissue  may  change  into  fat  cells, 
the  tissue  as  a  whole  then  forming  adipose  tissue.  In  all  we  distinguish 
the  following  varieties  of  connective  tissue:  (1)  Embryonal;  (2)  mucous; 
(3)  reticular;  (4)  loose  fibro-elastic  or  areolar;  (5)  dense  fibrous;  (6) 
dense  elastic;  (7)  adipose;  (8)  adenoid;  (9)  cartilage;  (10)  bone. 

Embryonal  Connective  Tissue.— Embryonal  connective  tissue  (Figs. 
55  and  56)  occurs  not  only  in  fetal  and  infantile  life,  but  also  during  the 
regeneration  of  destroyed  connective*  tissue  areas  and  in  pathological 
neoplasms.  It  is  distinctly  cellular  in  character.  Its  cells  are  spindle- 
shaped  and  stellate,  are  much  branched,  and  through  their  larger  proc- 
esses they  frequently  anastomose. 

The  fibers  are  extremely  fine;  they  are  not  usually  arranged  in  bun- 
dles, but  form  a  delicate  network  which  permeates  the  ground  substance 
in  every  direction.  In  the  very  immature  types  the  fibers  are  all  of  the 
collagenous  variety ;  delicate  elastic  fibers  appear  later.  The  fluid  ground 
substance  forms  an  abundant  mass  of  tissue  juice  which  occupies  the 
meshes  of  the  fibrous  net.  The  earliest  developmental  stages  are  ideuti- 


54  CONNECTIVE  TISSUE— CARTILAGE— BONE 

cal  with  mesenchyma;  from  the  viewpoint  of  progressive  differentiation 
it  properly  heads  the  list  of  connective  tissues. 

Mucous  Connective  Tissue. — Mucous,  gelatinous  or  mucoid  connec- 
tive tissue  occurs  only  in  the  umbilical  cord,  where  it  forms  the  'jelly  of 
Wharton,'  and  in  the  vitreous  humor  of  the  eye.  Its  semifluid  ground 
substance  is  of  a  gelatinous  consistence  and  forms  the  greater  portion  of 
the  tissue;  in  the  vitreous  humor  there  is  little  else. 

The  cells  are  mostly  of  the  branched  lamellar  variety,  are  few  in  imm- 


FIG.  62. — GELATINOUS  CONNECTIVE  TISSUE  FROM  THE  UMBILICAL  CORD  OF  A  XEW- 
BORN  INFANT. 

Safranin  and  water  blue.     X  410. 

ber  in  the  vitreous,  but  more  abundant  in  the  umbilical  cord.  In  the 
vitreous  humor  also,  there  arc  very  few  fibers;  those  which  are  present 
are  very  line  and  form  a  delicate  reticulum.  In  the  umbilical  cord  the 
fibers  are  more  abundant,  and  possess  a  tendency  to  form  bundles  which 
are  disposed  in  parallel  cylindrical  layers  around  the  large  blood- 
vessels. Elastic  fibers  are  wanting.  This  type  lacks  also  nerves,  blood- 
vessels and  lymph-vessels;  the  two  large  umbilical  arteries  and  the 
umbilical  vein  have  no  vascular  connection  with  the  mucous  tissue  of 
the  cord. 

The  essential  chemical  body  in  mucus  is  mucin,  a  glycoproteid.  The 
most  typical  mucous  substance  is  the  secretory  content  of  goblet  cells. 
The  mucus  of  embryonic  and  gelatinous  connective  tissue  is  closely 


CONNECTIVE  TISSUE 


55 


similar.  Less  closely  similar  'mucous'  substances  of  the  more  compact 
connective  tissues  are  properly  designated,  mucoids. 

Reticular  Tissue  (Reticulum). — Reticular  tissue  occurs  as  the 
stroma  of  adenoid  tissue  in  the  lymphatic  glands  and  other  lymphoid  or- 
gans, and  according  to  Mall  (Johns  Hopkins  Hosp.  Rep.,  1896),  is  found 
also  in  the  membraria  propria  of  the  secreting  tubules  of  the  stomach, 
intestine,  kidney,  tostis,  and  thyroid,  and  in  the  marrow  of  bone  and  the 
walls  of  the  pulmonary  air  sacs. 

Like  the  other  connective  tis- 
sues, reticular  tissue  consists  of 
cells,  fibers,  and  ground  substance ; 
the  latter,  however,  is  no  more 
than  a  fluid  tissue  juice  which,  at 
least  in  the  lymphoid  organs,  is 
identical  with  the  lymph.  The 
fibers  are  extremely  fine  and  are 
arranged  in  slender  bundles,  which 
freely  anastomose  to  form  a  deli- 
cate close-meshed  reticulum.  In- 
dividual fibers  can  be  readily  dem- 
onstrated in  these  bundles  only 
after  the  action  of  alkalies,  diges- 
tion by  artificial  gastric  juice,  or 
oy  other  methods  of  dissociation, 
yet  on  careful  examination  indica- 
tions of  fibrillar  structure  can  be 
seen  in  the  reticulum  of  fresh  tis- 
iiie  and  in  ordinary  microscopical 

preparations.  The  chemical  reactions  of  the  reticular  fibers  are  similar 
to  those  of  collagenous  fibers  except  that  the  former  are  much  less  readily 
digested  by  artificial  gastric  juice. 

Flattened  connective  tissue  cells  clasp  the  bundles  of  reticular  fibers ; 
they  are  mostly  found  at  the  intersections  of  the  anastomosing  bundles. 
This  fact  was  accountable  for  the  former  theory,  which  regarded  reticu- 
lar 1  issue  as  formed  by  the  anastomosing  branches  of  stellate  cells.  The 
careful  investigations  of  Carlier  (Jour.  Anat.  and  Physiol.,  1895)  and 
others  have  shown  the  true  nature  of  the  lamellar  cells  and  their  under- 
lying fiber  bundles. 

The  fibers  of  reticular  tissue  very  closely  resemble  the  collagenous 
fibers  of  areolar  tissue,  but  differ  from  them  in  having  a  clearer,  more 


FIG.  63. — RETICULUM  OF  A  CERVICAL 
LYMPH  NODE  OF  MAN,  FROM  A  THIN 
SECTION  FROM  WHICH  THE  LYMPHATIC 
CORPUSCLES  HAD  BEEN  PARTIALLY 
WASHED  OUT. 

a,  polynuclear  lymphatic  corpuscle;  b, 
large  mononuclear  cell;  c,  connective  tis- 
sue cells  of  the  reticular  tissue;  d,  fibrous 
bundle  of  the  reticulum;  e,  small  mono- 
nuclear  lymphocyte.  Hematein  and 
eosin.  X  500. 


56  CONNECTIVE  TISSUE— CARTILAGE— BONE 

highly  refractive  appearance.  Their  digestion  in  pepsin  begins  only  after 
an  interval  of  two  hours,  while  white  fibers  are  digested  in  a  few  minutes ; 
they  also  stain  less  readily  than  white  fibers  and  yield  reticulin,  which 
differs  somewhat  from  the  gelatin  of  white  fibrous  tissue.  The  intimate 
histologic  relation  between  the  reticular  and  white  fibrous  tissue  is  shown 
by  the  fact  that  the  two  tissues  are  frequently  continuous  and  exhibit 
similar  staining  reactions. 

Mall  (Amer.  Jour,  of  Anat.,  1902)  has  attempted  to  show  that  reticu- 
lar tissue  should  be  considered  as  that  form  of  connective  tissue  which 
has  been  least  differentiated  from  the  embryonic  mesenchymal  type. 
He  accordingly  considers  the  cells  of  the  reticulum  as  formed  by  the  un- 
differentiated  endoplasm,  and  the  reticular  fibers  as  representing  the 
specialized  exoplasm  of  this  most  primitive  type  of  true  connective 
tissue.  In  the  liver,  the  reticulum  arises  from  the  endothelial  cells  of  von 
Kuppfer  instead  of  from  mesenchyme  (Mall). 

Loose  Fibro-elastic  or  Areolar  Connective  Tissue. — Loose  fibro- 
elastic  or  areolar  connective  tissue  (Fig.  57)  is  the  most  widely  distrib- 
uted of  all  the  varieties;  it  fills  all  otherwise  unoccupied  spaces  within 
the  body,  and  in  all  microscopical  sections  areolar  tissue  is  almost  in- 
variably to  be  found.  It  is  also  known  as  loose  connective  tissue  in.  con- 
tradistinction to  the  more  compact  or  dense  varieties.  This  tissue  con- 
nects the  skin  with  the  underlying  structures,  maintains  the  position  and 
relation  of  adjoining  muscles,  surrounds  the  heart  and  its  great  vessels, 
envelops  the  abdominal  viscera  as  submucous  and  subserous  sheets,  occu- 
pies the  spaces  of  the  mediastinum,  and  fills  similar  intervals  between 
the  various  organs  in  all  parts  of  the  body.  Areolar  tissue  of  course 
varies  in  the  degree  of  its  laxity  or  density. 

The  ground  substance  of  areolar  tissue  is  a  coagulable  fluid,  the  tissue 
juice.  Solutions  of  silver  nitrate  injected  into  the  interstices  of  areolar 
tissue  coagulate  its  tissue  juice  or  ground  substance  and  darken  it 
slightly.  It  is  then  seen  to  be  permeated  by  broad  lymphatic  channels, 
which  are  lined  by  delicate  endothelioid  mesenchymal  cells  (W.  G.  Mac- 
Callum,  Arch.  f.  Anat.,  1902;  also  Bull.  Johns  Hopkins  Hosp.,  1903). 

Both  collagenous  and  elastic  fibers  occur  in  areolar  tissue,  the  former 
being  far  in  excess  of  the  latter.  The  comparatively  loose  reticular  ar- 
rangement of  the  fibers  of  fibro-elastic  tissue  affords  a  most  favorable 
opportunity  for  the  study  of  these  connective  tissue  elements.  . 

The  collagenous  or  white  fibers  in  mature  tissues  are  invariably  ar- 
ranged in  bundles  which  interlace  with  one  another  to  form  an  open  net- 
work. Each  bundle  consists  of  a  number  of  very  fine  fibers  whose 


CONNECTIVE  TISSUE  57 

course  is  characteristically  wavy  or  undulating.  Though  the  individual 
fibers  rarely  branch,  the  fiber  bundles  frequently  anastomose  with  one  an- 
other. The  white  fibers  are  readily  stained  with  most  'acid'  dyes,  and 
possess  a  special  affinity  for  acid  fuchsin.  Chemically  they  consist  of  the 
albuminoid  collagen,  which  on  boiling  in  water  yields  gelatin,  and  is 
readily  dissolved  by  boiling  in  dilute  acids  or  alkalies.  Collagen  fibers 
are  digested  by  artificial  gastric  juice  in  five  or  ten  minutes  but  are 


x         x 

^  ' 

x 
-»  ^ 

f' 


FIG.  64. — DENSE  FIBROUS  TISSUE  FROM  THE  TENDON  OF  ONE  OF  THE  OCULAR 
MUSCLES  OF  A  CHILD. 

Hematein  and  eosin.     X  550. 

scarcely  altered  after  several  hours  when  acted  upon  by  solutions^of  paii- 
creatin.  After  boiling,  however,  white  fibers  are  readily  digested  by  pan- 
creatin.  In  dilute  acids  they  swell  and  become  transparent. 

The  elastic  fibers  of  areolar  tissue,  in  comparison  with  the  collagenous 
fibers,  are  few  in  number.  They  occur  as  isolated  fibers — never  in  bundles 
— which  frequently  branch  and  anastomose,  forming  in  this  way  a  very 
fine  net  with  wide  meshes,  within  which  are  the  interlacing  bundles  of 
white  fibers.  The  elastic  fibers  exist  under  a  certain  tension  during  life, 
so  that  their  course  under  favorable  conditions  is  invariably  straight. 
When  areolar  tissue  is  removed  from  the  body  this  tension  is  frequently 
relieved  and  the  elastic  fibers  then  curl  up,  especially  at  their  free  ends. 


58 


CONNECTIVE  TISSUE— CARTILAGE— BONE 


Under  these  conditions  they  are  no  longer  straight,  but  present  a  grace- 
fully curved  contour.  The  elastic  fibers  also  possess  a  glassy,  shining,  or 
highly  refractive  appearance,  the  collagenous  fibers  by  comparison  look- 
ing dull  and  opaque. 

Elastic  fibers  stain  but  slightly  with  most  dyes;  they  are  readily 
colored  by  orcein  and  by  Weigerfs  elastic  tissue  stain  (resorcin-fuchsin), 
both  of  which  serve  as  specific  dyes  for  these 
fibers,  coloring  the  fibers  dark  brown  or 
black.  Elastic  fibers  are  not  dissolved  by 
dilute  acids  or  alkalies  even  when  boiled,  and 
are  only  digested  by  artificial  gastric  juice 
after  a  lapse  of  several  hours ;  they  are,  how- 
ever, readily  digested  in  faintly  alkaline  solu- 
tions of  pancreatin.  They  consist  of  the  al- 
buminoid body,  elastin,  which  on  boiling  does 
not  yield  gelatin.  Both  collagenous  and  elas- 
tic fibers  arise  by  a  similar  process  involving 
transformation  of  the  exoplasm  of  their  re- 
spective fibroblast  progenitors  into  a  fibrillar 


FIG.  65. — LONGITUDINAL  SECTION  OF  TENDON  OF 
HUMAN  FINGER. 

Only  the  nuclei  of  the  tendon  cells  are  conspicu- 
ous, scattered  in  rows  among  the  collagenous  fibrils. 
The  rows  of  nuclei  mark  the  boundaries  of  the 
primary  bundles.  X  750. 


FIG.    66.  —  PORTION    OF 
TENDON  FROM  A  Cow. 

conn.  t.  c.,  connective  tis- 
sue cells  (tendon  cells)  seen 
from  the  side  and,  in  one  case, 
from  the  surface.  (From 
Dahlgren  and  Kepner's  "Ani- 
mal Histology,"  Macmillan 
Co.) 


structure.     Whether  the  fibers  are  deposited  as  such  or  arise  by  coales- 
cence of  more  fundamental  granular  elements  is  a  disputed  point. 

The  cells  of  areolar  tissue  are  few  in  number,  but  may  include  any 
of  the  several  varieties,  though  lamellar  and  spindle  cells  together  with 
leukocytes  form  the  more  common  types.  Many  of  the  lamellar  cells  are 


CONNECTIVE  TISSUE 


closely  applied  to,  or  even  wrapped  around  the  bundles  of  white  fibers. 
Fat  cells  occur  in  considerable  numbers  in  all  areolar  tissue  and  in  some 
places  are  aggregated  into  large  groups  which  form  lobules  of  fatty 
tissue. 

Dense  Fibrous  Tissue. — In  dense  fibrous  tissue  the  ground  substance 
is  comparatively  deficient.  Large  bundles  of  collagenous  fibers  are  ar- 
ranged in  approximately  parallel  rows,  and  are  so  closely  packed  as  to 


FIG.  67. — TRANSVERSE  SECTION  OF  PORTION 

OF  TENDON  OF  HUMAN  FINGER. 
a,  three-winged  cell;  b,  four-winged  cell; 
c,  primary  bundle,  completely  ensheathed  by 
the  wings  of  tendon  cells,  and  divisible  into 
still  smaller  bundles  of  collagenous  fibers 
outlined  by  finer  processes  of  the  wings. 
The  individual  fibers  are  not  shown.  Gold 
chlorid.  X  1000. 


FIG.   68. — PIECE   OF   TENDON   FROM 

TAIL  OF  WHITE  MOUSE. 
Between  the  bundles  of  connec- 
tive-tissue fibrils  are  cells  arranged 
in  rows.  Some  are  seen  in  surface 
view,  and  others  in  optical  section. 
X  400.  (From  Szymonowicz-Mac- 
Callum,  "Histology  and  Microscopic 
Anatomy.") 


form  a  dense,  firm,  highly  resistant  tissue.  Its  scanty  connective  tissue 
cells  are  of  the  lamellar  variety  and  are  usually  arranged  in  rows  which 
occupy  the  interstices  between  the  parallel  fiber  bundles. 

Dense  fibrous  tissue  occurs  typically  in  tendons;  in  these  the  connec- 
tive tissue  cells  often  have  a  peculiar  quadrate  shape  and  are  arranged 
in  rows  of  exceptional  regularity  (Figs.  G'4-07).  These  should  be  studied 
in  dissociated  tendinous  tissue.  It  also  forms  the  ligaments,  the  fasciae, 
the  muscular  sheaths  (aponeuroses),  and  the  enveloping  capsules  of  many 
of  the  viscera.  Thus  it  surrounds  the  liver,  kidney,  lymphatic  nodes,  and 
other  organs;  it  also  forms  the  valves  of  the  heart,  the  tendinous  rings 


60 


CONNECTIVE  TISSUE— CAKTILAGE— BONE 


FIG.  69. — ISOLATED  TENDON  CELLS. 

A,  with  two  'wings';  B,  with  four  'wings.'     (From  Maximow,  after  Tourneau.) 
X  1000. 

which  surround  the  cardiac  orifices,  and  the  chordae  tendineae  which  are 
attached  to  its  valves ;  and  in  general,  it  is  found  wherever  great  firmness 

and  resistance  are  required. 

Elastic  fibers  in  this  tissue  are 
relatively  few  in  number  and  are  so 
obscured  by  the  dense  bundles  of  white 
fibers  as  to  be  scarcely  demonstrable 
except  by  means  of  the  specific  stains. 
Tendon  will  be  further  discussed  in 
connection  with  striped  muscle. 

Dense  Elastic  Tissue.— I  n  this 
form  of  tissue  the  elastic  fibers  are  de- 
veloped at  the  expense  of  the  colla- 
genous  fibers.  The  ground  substance 
is  insignificant  in  amount,  and  the 
connective  tissue  cells  are  scanty  and 
are  confined  to  the  white  fibrous 
sheaths  in  which  the  elastic  fibers  are 
enveloped.  The  elastic  fibers  are  of 
very  large  size  (10  to  15  /x  )  as  com- 
pared with  those  of  other  forms  of 
'connective  tissue.  But  except  for  their 
larger  size,  these  fibers  have  the  same 
peculiar  characteristics  as  the  elastic 
fibers  of  areolar  tissue.  In  their 
straight  course,  frequent  branches,  and 
their  glistening,  highly  refractive  appearance,  as  also  in  their  character- 
istic reactions  to  specific  dyes  and  other  reagents,  these  fibers  are  identical 


FIG.  70. — COARSE  ELASTIC  FIBERS 

FROM  THE    LlGAMENTUM    NlJCHJE 
OF  THE  Ox. 

Isolated  by  teasing.     Partly  dia- 
grammatic.    X  about  250. 


CONNECTIVE  TISSUE 


61 


FIG.  71. — TRANSECTION  OF  A  FASCIC- 
ULUS OF  THE  LlGAMENTUM  NUCH^B 

OF  THE  Ox,  SHOWING  THE  VERY 
LARGE  ELASTIC  FIBERS  EMBEDDED 
IN  A  VERY  DELICATE  NETWORK  OF 
COLLAGENOUS  FlBERS. 

Picro-fuchsin.     X  550. 


with   the   elastic   fihers  of  the   other 
types  of  connective  tissue. 

The  elastic  fibers  are  bound  to- 
gether by  delicate  sheaths  of  very  fine 
collagenous  fibers,  and  are  united  into 
bundles  by  coarser  bands  of  fibrous 
tissue.  Elastic  tissue  is  found  in  the 
ligamenta  flava,  the  stylohyoid  liga- 
ment and  in  the  ligamentum  nuchaB 
(Svhitleather')  of  quadrupeds.  In 
these  locations  it  occurs  in  consider- 
able quantity  and  has  a  peculiar  yel- 
lowish color ;  it  is  for  this  reason  that 
it  is  frequently  described  as  yellow 
elastic  tissue.  It  occurs  also  as  fen- 
estrated  membranes  in  arteries.  These  are  formed  by  a  coalescence  of 

neighboring  fibers.  In  the  process  of 
occlusion  of  the  postfetal  ductus  ar- 
teriosus  of  the  pig  by  increase  in  the 
amount  of  the  elastic  tissue  in  the 
wall  of  the  artery,  the  new  elastic 
fibers  arise  both  from  latent  fibro- 
blasts  and  by  delamination  of  fibers 
from  preformed  elastic  tissue  (J.  P. 
Schaeffer,  Jour.  Exp.  Med.,  vol.  19, 
1914). 

Adipose  Tissue  (Fat  Tissue).— 
Wherever  areolar  tissue  occurs,  adipose 
tissue  may  also  be  found ;  its  distribu- 
tion is  therefore  identical  with  that  of 
areolar  tissue.  It  forms  a  consider- 
able mass,  panniculus  adiposus,  be- 
neath the  skin  of  many  parts.  In  it 
are  embedded  the  kidneys,  adrenals, 
and  many  lymphatic  nodes.  The  mes- 
entery and  omentum  are  freely  sup- 
plied with  fat.  The  same  tissue  is 
found  in  the  grooves  of  the  heart  wall 
and  it  also  occupies  the  spaces  of  the  mediastinum. 

Adipose  tissue  is  composed  of  lobules  or  groups  of  fat  cells  which  are 


t.  c. 


ffy 

S/ 


FIG.  72. — PORTION  OF  LIGAMENTUM 

NUCHJE  OF  Ox. 

conn.  t.  c.,  connective  tissue  cells. 
(From  Dahlgren  and  Kepner.) 


62  CONNECTIVE  TISSUE— CARTILAGE— BONE 

supported  by  fibrous  bands  and  septa  and  are  abundantly  supplied  with 
small  blood-vessels. 

The  fat  cells  arise  from  the  connective  tissue  cells  bv  a  deposil 
of  fat  droplets  within  the  cytoplasm  of  the  latter.  These  droplets 
continue  to  increase  in  number  and  fuse  with  each  other  to  form  globules 


i.e. 


FIG.  73. — PORTION  OF  A  FAT  LOBULE  FROM  THE  AREOLAR  CONNECTIVE  TISSUE  SUR- 
ROUNDING THE  ESOPHAGUS  OF  A  CAT. 

cap.,  capillary;  ct.  c.,  nucleus  of  a  connective  tissue  cell;  /.  c.,  fat  cell  showing 
nucleus;  tr.,  trabecula  of  nbro-elastic  connective  tissue.     X  500. 

of  increasing  size,  until  the  cytoplasm  finally  becomes  so  excavated  as  to 
form  a  mere  limiting  membrane  or  cell  wall  (Fig.  74).  The  nucleus  is 
pushed  to  one  side  in  this  process  and  is  flattened  against  the  cell  mem- 
brane ;  it  is  usually  embedded  in  a  remnant  of  granular  cytoplasm.  Be- 
ing thus  distended  with  fluid  fat,  the  cell  acquires  a  spheroidal  shape. 
The  routine  specific  stains  for  fat  are  osmic  acid,  which  colors  the 


CONNECTIVE  TISSUE 


FIG.  74.— A  GROUP  OF  FAT 
CELLS  FROM  THE  SUBCU- 
TANEOUS TISSUE  OF  A 
YOUNG  RABBIT. 

Cells  a  show  stages  in  de- 
velopment; cell  6  is  cut  tan- 
gentially  through  the  nucle- 
ated pole.  X  iOOO. 


fat  globules  black;  sudan  III,  which  gives  a 
red  reaction  :  and  srharlack  II  (fettponceau), 
which  also  stains  fat  red.  For  the  successful 
application  of  these  stains  it  is  required  that 
the  tissue  has  not  been  previously  subjected 
to  treatment  involving  the  use  of  alcohol  or 
ether,  since  these  reagents  extract  fat  from 
the  cells.  Fat,  in  cooling,  solidifies  and  pre- 
cipitates delicate  threads,  the  margarin  crys- 
tals. 

During  periods  of  starvation  or  malnu- 
trition, at  which  time  fat  decreases  greatly 
in  volume,  many  of  the  fat  cells  return  to  a 
condition  which  approximates  their  former 
state.  As  the  fat  is  removed  the  cytoplasm 
of  the  cell  increases  in  amount,  but  assumes 
a  peculiar  fluid  appearance  and  is  not  read- 
ily colored  by  the  usual  dyes.  These  cells, 
which  still  contain  a  number  of  fat  droplets, 
are  known  as  'serous'  fat  cells. 

The  origin  of  the  fat  cell  is  still  somewhat  in  doubt.  It  was  for- 
merly thought  that  it  might 
result  from  a  deposit  of  fat 
within  any  of  the  connective 
tissue  cells.  A  second  theory 
maintains  that  it  arises  only 
from  a  special  fat-forming 
connective  tissue  cell.  The 
demonstration  of  large  num- 
bers of  peculiar  ovoid  granular 
cells  within  areas  where  fat 
cells  were  undoubtedly  form- 
ing in  fetal  and  young  sub- 
jects, and  the  demonstration 
of  similar  cells  in  areas  show- 
ing fat  formation  in  adult  tis- 
sues, has  .lent  support  to  the 
hypothesis  that  these  granular 

cells  are  the  only  progenitors  of  the  fat  cells  (Shaw,  Jour.  Anat.  and 
Physiol.,  1H01).     According  to  Weiskoiten  and  Steensland  (Anat.  l?ec., 


FIG.  75  — FAT  CELLS  FROM  A  TEASED  PREP- 
ARATION OF  ADIPOSE  TISSUE  OF  MAN. 
X  110. 


-  CONNECTIVE  TISSUE— CARTILAGE— BONE 


FIG.  76. — ADIPOSE  TISSUE. 

The  fat   cells  have  been  blackened  by   osmium 
tetroxid.     X  110. 


8,  2,  1914)  fat  cells 
can  arise  also  by  a 
process  involving  the 
enclosure  of  free  fat 
spherules  by  endothe- 
lial  cells.  They  suggest 
that  fat  cells  may  be 
modified  endothelial 
cells  rather  than  mod- 
ified fibroblasts. 

The  forerunners  of 
the  original  smallest 
fat  droplets  are  gran- 
ules (Altmann,  1890). 
In  the  subcutaneous 
tissue  of  Myxine  (Hag- 
fish)  embryos,  Schrei- 

ner  (Anat.  Anz.  48,  7,  1915)  has  described  the  process  of  fat  elaboration 

in  minute  detail.    The  pre-fat  granules  originate  from  rod-like  chromidia 

('mitochondria')     by     process 

of   segmentation.      The   chro- 
midia arise  as  nucleolar  buds 

which     wander     through    the 

nucleus  and  traverse  the  nu- 
clear  membrane   as   spherical 

granules.        These      'primary 

granules'   elongate   into   rods, 

and  subsequently  segment  into 

'secondary     granules/     which 

liquefy   and  coalesce  to  form 

the    definitive    fat    spherules. 

This    important    investigation 

suggests  a  functional  role  for 


FIG.  77. — DEVELOPING  ADIPOSE  TISSUE  FROM 
THE  SUBCUTANEOUS  TISSUE  OF  AN  INFANT. 


The  fat  has  been  removed  by  immersion  in 
alcohol  and  ether.  The  polygonal  outlines  of 
the  fat  cells  are  well  shown.  Within  many  of 
them  is  seen  the  finer  cytoplasmic  network  by 
which  the  inclosed  droplets  of  fat  were  in- 
vested; this  network  had  not  been  completely 
replaced  by  the  accumulation  of  fat.  Hema- 
tein  and  eosin.  Photo.  X  325. 


mitochondria  in  terms  of  a 
nutritive  material  upon  which 
cell  metabolism  and  differen- 
tiation may  depend.. 

Lymphoid   Tissue    (Ade- 
noid Tissue). — Lymphoid  tissue  is  a  reticular  tissue  the  meshes  of  whose 
network  are  occupied  by  a  closely  packed  mass  of  lymphocytes,  cells  with 


FIG.  78. — RETICULUM  FROM  THE  MUCOSA  OF  THE  FUNDUS  REGION  OF  THE  DOG'S 

STOMACH. 

The  section  was  made  parallel  to  the  surface  and  the  glandular  tissue  removed 
by  shaking  in  water.    Picro-carmin.     X  125.     (After  Mall.) 


Lymph  smu 


Cortical 
ubstance 


Capsule     ^ 
Medullary  cord 


J  ^Trabeculx 

Medullary  substance 

FIG.  79. — SECTION  THROUGH  A  SMALL  LYMPH  NODE  OF  A  DOG.     X  20. 
(From  Szyrnonowicz-MacCallum,  "Histology  and  Microscopic  Anatomy.") 
6  65 


CONNECTIVE  TISSUE— CARTILAGE— BONE 


a  deeply  staining  nucleus  enveloped  by  a  narrow  shell  of  homogeneous 
slightly  basophilic  cytoplasm.  The  lymph  cells  (lymphocytes)  are  so 
closely  packed  that  it  is  almost  impossible  to  distinguish  the  fine  threads 
of  the  reticular  stroma,  except  in  those  portions  where  some  of  the 
lymphatic  cells  have  been  washed  out  or  displaced  in  the  preparation  of 
fc  n  h  the  specimen.* 

The   density   of   the   lymphoid 
tissue  varies  much,  however,  in  dif- 


FIG.  80. — FROM  A  SECTION  THROUGH  THE 
MEDULLA  OF  A  CERVICAL,  LYMPH  NODE 
OF  MAX. 

a,  a  fcord'  of  dense  lymphoid  tissue; 
1),  looser  lymphoid  tissue  of  the  medullary 
sinuses;  c,  the  margin  of  a  fibrous  tra- 
becula;  d,  nucleus  of  the  connective  tis- 
sue reticulum;  e,  endothelial  lining  of  the 
lymphatic  sinus.  Hematein  and  eosin. 
X  475. 

mouth,"  tongue,  pharynx,  esophagus, 
In  the  basement  membranes  of 
kidney,  tear  and  mammary — and  in 
cells  of  the  umbilical  cord,  Mallorv 


,.  n     ,1  m1 

portions  of  the  same  organ.  The 
denser  accumulations  of  lymphoid 
corpuscles  may  form  either  ovoid 
lymph  nodules  or  follicles,  or  long 

<lcnse  trabeculse>  the  lymphatic 
ro/v/x,  which  are  surrounded  by 

i  ,.  »  i  i.    -a  A: 

looser  portions  of  lymphoid  tissue. 
Lymphatic  corpuscles  are  fre- 
quently infiltrated  into  the  connec- 
tive tissue  of  the  mucous  mem- 
branes, where  they  form  irregular 
collections,  which  may  be  termed 
diffuse  lymphoid  tissue,  in  contra- 
distinction to  compact  lymphoid 
tissue,  which  occurs  in  the  lymph 
nodes,  tonsils,  thymus,  and  spleen, 
and  in  the  aggregate  and  solitary 
nodules  of  the  intestinal  canal. 
Diffuse  lymphoid  tissue  is  found  in 
the  mucous  membranes  of  (A)  the 
respiratory  tract  —  nose,  nasophar- 
ynx, larynx,  trachea,  and  bronchi; 
and  (B)  the  alimentary  tract  — 
stomach,  and  intestines. 
certain  tubular  glands  —  e.g.,  sweat, 
the  peripheral  portion  of  the  large 
(Jour.  Med.  Ees.,  1903  and  1905) 


*  Mall's  technic  for  this  purpose  consists  in  injecting  gelatin  into  a  fresh 
lymph  organ  (e.  g.,  spleen),  freezing  the  tissue,  and  placing  thin  sections  into 
warm  water  when  the  lymphocytes  are  largely  carried  away  by  the  dissolving 
gelatin  leaving  the  reticulum  free. 


CAETILAGE  67 

has  discovered  robust  fibers  extending  also  from  cell  to  cell,  resembling 
somewhat  white  fibers,  but  unrelated  by  transition  elements  to,  and  dif- 
fering microchemically  from,  collagenous  fibers.  They  are  said  to  be 
similar  to  the  fibrils  of  neuroglia  cells  of  nervous  tissue  and  to  the 
border  or  myoglia  fibrils  of  plain  muscle  cells. 

BLOOD  AXD  NERVE  SUPPLY  OF  THE  CONNECTIVE  TISSUES 

The  connective  tissues,  but  especially  the  areolar  variety,,  form  a 
supporting  substance  through  which  the  various  blood  and  lymphatic 
vessels  and  nerve  trunks  are  distributed  to  all  portions  of  the  body. 
Within  the  connective  tissues  these  vessels  are  everywhere  present,  and 
from  them  the  connective  tissue  itself  receives  its  supply  of  capillary 
vessels  and  terminal  nerve  fibrils. 

The  vascular  supply  of  the  connective  tissues  is  very  abundant. 
Small  arteries,  which  are  derived  from  the  main  trunks,  form  a  capillary 
plexus  throughout  the  tissue,  the  capillaries  finally  reuniting  to  form  the 
veuules. 

It  is  in  this  capillary  plexus  that  the  fluid  portions  of  the  blood  exude 
into  the  surrounding  peri  vascular  lymphatic  or  tissue  spaces  of  the  con- 
nective tissue.  The  tissue  juices  which  arise  in  this  manner  are  most 
active  agents  in  the  physiological  processes  of  assimilation.  From  the 
tissue  juice  spaces,  lymph  reenters  the  abundant  capillary  lymphatic 
vessels  to  be  finally  returned  to  the  venous  blood.  This  transfer  is 
mediated  by  process  of  filtration  and  osmosis,  the  tissue  spaces  being 
generally  regarded  as  closed  spaces  making  no  direct  connection  with 
the  lymphatic  terminals.  Of  the  several  varieties  of  connective  tissue, 
the  adipose  possesses  the  most  abundant  blood  supply;  the  lymphoid,  on 
the  other  hand,  is  most  richly  supplied  with  lymph. 

Abundant  nerves  are  distributed  to  the  connective  tissues,  some  of 
which,  the  sympathetic  nerves,  supply  its  blood-vessels  while  others, 
medullated,  terminate  in  special  forms  of  sensory  nerve  end-organs. 


CARTILAGE 

Cartilage  is  a  dense,  firm,  but  elastic  substance,  resembling  connective 
tissue  in  that  it  is  developed  from  similar  mesodermal  cells.  It  contains 
a  ground  substance,  the  cartilage  matrix,  and  at  times,  fibers  which 
may  be  either  collagenous  fibers  or  elastic.  The  presence,  absence,  or 


68  CONNECTIVE  TISSUE— CARTILAGE— BONE 

character  of  these  fibers  determines  the  variety  of  cartilage.  Three 
varieties  are  thus  distinguished:  hyaline  cartilage,  in  which  no  specific 
fibers  can  ordinarily  be  demonstrated  within  the  matrix ;  elastic  cartilage, 
whose  matrix  is  permeated  by  elastic  fibers;  and  fibro cartilage,  whose 
matrix  contains  collagenous  fibers. 


*   ••    •    t 

:•*  ", c 


FIG.  81. — TRANSECTION  OF  A  PLATE  OP  HYALINE  CARTILAGE,  FROM  THE  TRACHEA  OP 

A  CHILD. 

The  margin  of  the  fibrous  perichondrium  can  be  seen  on  either  side  of  the  plate  of 
cartilage,  in  the  upper  right  and  lower  left  hand  corners  of  the  figure.  Hematein 
and  eosin.  Photo.  X  400.  The  dark  bodies  are  shrunken  cells  within  lacunae. 

Hyaline  Cartilage. — This  is  the  most  abundant  of  the  three  varie- 
ties, commonly  known  as  gristle.  It  is  found  in  the  respiratory  system, 
forming  the  cartilages  of  the  nose,  larynx,  trachea,  and  bronchial  tubes; 
in  the  costal  cartilages  of  the  ribs;  as  articular  cartilages  covering  the 
ends  of  long  bones ;  and  in  the  fetus,  where  in  the  course  of  development 
of  the  bones,  the  entire  skeleton,  excepting  only  the  flat  bones  of  the  skull 
and  face,  at  first  consist  of  hyaline  cartilage.  In  most  of  these  loca- 
tions the  cartilage  occurs  as  platelike  masses,  which  are  invested  by  a  vas- 


CARTILAGE 


cular  membrane  of  dense  fibre-elastic  tissue.  This  membrane  is  the 
perichondrium.  The  inner  portion  of  this  membrane  is  richly  supplied 
with  small  cells,  and  it  is  from  this  cell  layer,  the  chondrogenetic  layer,, 
that  the  cartilage  is  presumably  developed. 

The  cartilage  blastema  is  essentially  mesenchyma.  The  chondro- 
genetic cells  of  this  pre cartilage  multiply,  and  deposit  about  themselves 
the  structureless  mass  which  first  forms  merely  a  capsule  to  the  cell, 
but  which  as  it  increases  in  amount,  separates  the  various  cells  by 
wider  areas  and  becomes  the  cartilage  matrix.  The  cells,  which  in  the 
perichondrium  are  small  and 
decidedly  flattened,  likewise  in- 
crease in  size  during  this  proc- 
ess, and  become  more  nearly 
spherical,  so  that  those  cartilage 
cells  which  lie  near  the  center  of 
the  cartilaginous  plates  are 
spheroidal  in  shape,  while  those 
toward  the  surface  are  more  and 
more  flattened  or  elongated, 
their  long  axes  gradually  re- 
volving from  a  perpendicular 
position  in  the  center  of  the 
plate  to  one  parallel  with  the 
perichondrium  at  the  surface. 
Each  cartilage  cell  is  inclosed 
within  a  small  space  or  lacuna, 
which  during  life  it  entirely  fills. 

Cell  multiplication  in  carti- 
lage is  peculiar  in  that  cell  di- 
vision occurs  within  a  firm  capsule  and  results  in  the  formation  of  two 
daughter-cells,  which  at  first  lie  within  the  same  encapsuled  space.  These 
two  cells  may  each  again  undergo  division  within  the  same  space  with 
formation  of  four  new  cells.  As  a  result  of  this  peculiar  method  of  cell 
division  the  cartilage  cells  are  arranged  in  groups  of  two,  four,  or  even 
eight  cells.  Each  of  the  cells  in  the  group  deposits  its  capsule,  and  thus 
forms  a  matrix  about  itself,  so  that  the  increasing  space  thus  produced 
between  the  cells  of  a  group  may  separate  them  until  they  become  com- 
pletely isolated  cartilage  cells  each  within  its  own  lacuna.  In  this  way 
the  matrix  of  the  cartilage  is  produced.  Enlargement  of  a  cartilage  plate 
occurs  through  a  combination  of  interstitial  and  perichondrial  growth. 


FIG.  82. — CELLS  AND  MATRIX  OP  HYALINE 
CARTILAGE  FROM  THE  WALL  OF  A  LARGE 
BRONCHUS  OF  MAN. 

The  grouping  in  pairs  and  fours,  and  the 
tendency  to  produce  a  so-called  'capsule,' 
are  especially  noticeable.  Hematein.  X550. 


70 


CONNECTIVE  TISSUE— CARTILAGE— BONE 


The  matrix  of  hyaline  cartilage  is  devoid  of  fibrous  or  cellular  structure. 
Chemically  it  consists  of  collagen,  chondromueoid  and  albuminoid  sub- 
stances. Von  Korff  (1914)  interprets  hyaline  matrix  as  being  composed 
of  matrical  fibrils  masked  by  a  homogeneous  cementing  substance. 

During  life,  or  if  the  tissue  is  examined  in  the  fresh  state,  the  car- 
tilage cell  entirely  fills  the  lacuna  in  which  it  lies.  But  shortly  after  death 
shrinkage  of  these  cells  begins,  so  that  after  some  hours  a  considerable 
space  intervenes  between  the  cell  and  the  wall  of  its  lacuna.  It  has  been 
supposed  that  this  space  was  occupied  during  life  by  lymph.  It  would, 

however,  seem  more  probable 
that  it  is  partially  the  result  of 
post-mortem  shrinkage  of  the 
cell. 

Frequently,  and  especially  in 
developing  cartilage,  concentric 
lines  may  be  seen  surrounding 
each  lacuna.  These  lines  have 
been  described  as  the  'cell  cap- 
sule/ They  appear  only  to  in- 
dicate the  successive  layers  of 
material  which  have  been  de- 
posited by  the  cell,  and  which 
have  fused  together  to  form  its 
surrounding  matrix. 

Cartilage  arises  from  a  mes- 
enchymal  syncytium  in  which 
the  matrix  is  formed  from  the 
exoplasm  of  the  syncytial  tissue, 

the  cartilage  cell  representing  its  endoplasm.  The  so-called  capsule  of 
the  cartilage  cell  would  accordingly  represent  the  partially  modified  bor- 
der line  between  the  original  endo-  and  exoplasm,  and  would  thus  cor- 
respond to  similar  conditions  which  are  observed  in  other  forms  of  devel- 
oping connective  tissue. 

Cartilage  cells  frequently  contain  small  droplets  of  fat,  and  these  may 
coalesce  until  the  cell  is  completely  transformed  into  a  fat  cell.  Isolated 
masses  of  adipose  tissue,  resulting  from  the  transformed  groups  of  carti- 
lage cells,  thus  make  their  appearance  within  the  cartilaginous  plates.  This 
fatty  metamorphosis  is  most  marked  in  the  elastic  variety  of  cartilage. 

By  coloration  with  iodin,  glycogen  granules  may  also  be  demonstrated 
in  the  cartilage  cells. 


FIG.   83. — ELASTIC   CARTILAGE   FROM  THE 

HUMAN  EPIGLOTTIS,  SHOWING  THE  LARGE 

OVOID  CARTILAGE  CELLS  AND  THE  VERY 

DELICATE  RETICULUM  OF  ELASTIC  FIBERS. 

Ehrlich's  triacid  stain.     X  550. 


CARTILAGE  71 

Elastic  Cartilage. — Elastic  cartilage  occurs  in  the  external  ear,  in 
the  auditory  tube,  in  the  epiglottis  and  in  the  cuneiform  and  corniculate 
cartilages  and  the  vocal  processes  of  the  arytenoid  cartilages  of  the 
larynx.  It  is  essentially  hyaline  cartilage  the  matrix  of  which  has 
become  permeated  with  delicate  elastic  fibers  forming  a  dense  interlacing 
network.  The  large  spheroidal  cartilage  cell  lies  in  a  lacuna  bounded 
by  a  capsule  and  surrounded  by  a  layer  of  hyaline  matrix  free  of  elastic 
fibers.  The  plates  of  elastic  cartilage,  like  the  hyaline  variety,  are  sur- 
rounded by  a  dense  fibrous  perichondrium.  Neither  blood-vessels,  nerves, 
nor  lymphatics  are  distributed  within  the  matrix  of  elastic  cartilage. 

Fibrocartilage — This  tissue  forms  the  interarticular  cartilages  of  the 
lower  jaw,  the  clavicle,  and  the  knee;  composes  the  intervertebral  disks 
and  the  other  cartilaginous  symphyses  of  the  body;  lines  the  tendon 
grooves  of  the  bones,  and  forms  the 
glenoid  ligament  of  the  shoulder  and  the 
cotyloid  ligament  of  the  hip.  Fibrocar- 
tilage is  intermediate  in  structure  between 
hyaline  cartilage  and  such  very  dense 

fibrous  tissue  as  occurs  in  the  tendons  of 

FIG.  84. — FIBROCARTILAGE,  PROM 
muscles.     At  the  attached  margins  of  the      INTERVERTEBRAL  DISK  OF  Ox. 

cartilaginous  plates  its  tissue  is  continued 

by  imperceptible  gradations  into  the  surrounding  fibrous  connective  tis- 
sues. Like  the  other  forms  of  cartilage,  this  variety  is  also  non-vascular 
and  devoid  of  nerves. 

Microscopically,  fibrocartilage  differs  from  such  dense  white  fibrous 
tissue  as  is  found  in  the  ligaments  and  tendons,  in  that  the  meshes  of 
the  dense  fibrous  tissue  of  fibrocartilage  are  everywhere  permeated  by  a 
hyaline  matrix  in  which  here  and  there  are  small  groups  of  ovoid  car- 
tilage cells.  Each  cartilage  cell  is  occasionally  surrounded  by  a  charac- 
teristic, concentric,  lamellar  appearance  of  the  adjacent  matrix,  the  so- 
called  'capsule/  Plates  of  fibrocartilage,  unlike  the  other  varieties,  are 
not  surrounded  by  a  perichondrium. 

A  peculiar  sort  of  connective  tissue  of  entodermal  origin  is  found 
in  the  nuclei  pulposi  of  the  in  vertebral  disks.  It  is  the  sole  adult 
vestige  of  the  embryonic  axis,  the  notochord.  According  to  Williams 
(Amer.  Jour.  Anat.,  8,  3,  1908),  who  carefully  studied  its  cytomorphosis 
in  the  pig,  "It  is  primarily  cellular  and  epithelial;  later  it  becomes  a 


72  CONNECTIVE  TISSUE— CARTILAGE— BONE 

syncytial  network  with  a  mucin-like  substance  in  its  vacuoles ;  and  finally 
it  becomes  cellular  and  closely  resembles  cartilage."' 

The  Perichondrium. — The  perichondrium  is  a  dense  fibrous  mem- 
brane which  surrounds  each  individual  plate  of  cartilage.  It  is  continuous 
with  the  surrounding  connective  tissue,  and  is  well  supplied  with  blood- 
vessels and  lymphatics ;  it  may  also  contain  terminal  nerve  fibrils. 

The  cartilage  itself  is  an  absolutely  bloodless  and  nerveless  tissue. 
Neither  are  lymphatic  channels  demonstrable  within  the  cartilage  matrix. 


FIG.  85. — NOTOCHORDAL  TisstrE. 

A,  from  pig  embryo  of  150  mm.;  the  syncytium  contains  many  mucin-filled  spaces. 
X  800.  B,  from  nucleus  pulposus  of  an  adult  pig;  the  three  cells  shown  are  greatly 
vacuolated.  X  452.  (After  L.  W.  Williams,  Amer.  Jour.  Anat.,  8,  3,  1908.) 

After  long  maceration  or  artificial  digestion  the  matrix  assumes  a  granu- 
lar or  fibrous  appearance,  and  small  channels  have  been  demonstrated 
within  it,  which  have  been  said  to  connect  the  various  lacunae;  but  it  is 
evident  that  these  appearances  were  possibly  the  result  of  artificial  de- 
structive processes  and  could  not  therefore  be  considered  as  evidences  of 
the  presence  of  such  structure  in  living  cartilage. 


BONE 


General. — Bone  is  a  firm  calcareous  tissue  which  is  found  only  in 
the  skeletal  system.  In  the  flat  bones  it  forms  a  double  layer  of  dense 
osseous  tissue  between  which  is  a  narrow  space,  bridged  across  at  fre- 
quent intervals  and  thus  subdivided  into  a  number  of  compartments,  the 


BONE 


marrow  cavities.  This  central  stratum  presents  a  spongy  appearance  as 
compared  with  the  denser  periphery;  it  is  therefore  said  to  contain 
spongy  or  cancellous  ~bone,  while  the  more  superficial  lamellae  contain 
compact  bone. 

In  the  long  bones  a  similar  condi- 
tion exists  in  the  epiphyses,  which 
consist  of  a  wall  of  compact  bone 
within  which  the  marrow  cavity  is 
subdivided  by  bony  partitions  into 
numerous  compartments.  The  epi- 
physis  consists,  therefore,  of  spongy 
bone.  The  shaft  or  diaphysis  of  the 
bone,  however,  contains  a  single  large 
marrow  cavity  whose  walls,  except  for 
a  thin  layer  at  either  end,  consist  en- 
tirely of  compact  bone.  A  little 
spongy  structure  is  present  for  some 
distance  at  either  end  of  the  shaft,  in 
that  portion  which  adjoins  the  mar- 
row cavity. 

The  ends  and  facets  of  the  bones 
are  covered  by  a  disk  of  hyaline  car- 
tilage, which  forms  the  articulating 
surfaces  of  those  bones  which  enter 
into  the  formation  of  the  movable 
joints.  These  articular  cartilages  are 
peculiar  in  that  they  are  not  covered 
by  a  perichondrium,  and  their  deeper 
cells,  which  adjoin  the  bone,  are  so 
arranged  that  their  long  axes  are  per- 
pendicular to  the  free  surface,  as  is 
the  case  in  the  central  portion  of  free 
cartilaginous  plates.  Toward  the  free 
surface  of  the  cartilage  the  long  axis 
of  the  cell  lies  more  nearly  parallel  to 
the  surface,  as  is  likewise  the  case  at 
the  surface  of  cartilaginous  plates 

elsewhere.  In  the  long  bones  of  younger  individuals  a  plate  of  hyaline 
cartilage  is  found  also  at  the  epiphyxcul  lines  between  the  epiphysis  and 
the  diaphysis.  This  plate,  which  extends  through  the  entire  axis  of  the 


FIG.  86. — TRANSECTION  THROUGH  THE 
COMPACT  BONY  WALL  OF  A  HUMAN 
METACARPAL  BONE. 

a,  outer  circumferential  lamellae;  b, 
inner  circumferential  lamellae;  c, 
Haversian  canals;  d,  interstitial  lamel- 
lae; e,  lacunae,  with  delicate  radiating 
canaliculi.  From  a  thin  section  of 
ground  bone.  X  90.  (After  Kolli- 
ker.) 


CONNECTIVE  TISSUE— CARTILAGE— BONE 


bone,  becomes  ossified  later  in  life.  It  represents  the  line  of  growth,  and 
is  the  last  portion  of  fetal  cartilage  to  be  transformed  into  adult  bony 
tissue. 

Periosteum. — All  those  portions  of  the  bone  which  are  not  covered  by 
an  articular  cartilage  are  supplied  with  a  membranous  coat  of  fibrous 
tissue,  the  periosteum.  The  outermost  layer  of  this  membrane  consists 

of  interlacing  bundles  of  dense  fibrous 
tissue  in  which  are  the  larger  blood- 
vessels, whose  branches  are  distributed 
to  the  underlying  bone.  The  inner 
portion  of  this  layer  forms  a  firm 
fibro-elastic  stratum,  which  in  older 
individuals  is  closely  attached  to  the 
surface  of  the  bone.  The  periosteum 
of  developing  and  growing  bone,  how- 
ever, contains  a  third  or  innermost 
areolar  layer,  in  which  are  smalJ 
blood-vessels,  fine  connective  tissue 
fibrils,  and  numerous  small  osteogenic 
cells,  the  osteollasts.  After  growth 
of  the  bone  has  ceased,  the  deepest 
layer  of  the  periosteum  contains  few 
small  blood-vessels  and  only  occa- 
sional osteoblasts.  These  cells,  how- 
ever, are  present  in  sufficient  numbers 
to  accomplish  the  regeneration  of  the 
bone  after  destruction  of  its  osseous 
tissue. 

The  medullary  surface  of  the  bone 
is  likewise  supplied  with  an  osteo- 
genic membrane  of  fibrocellular  tis- 
sue, similar  to  the  innermost  layer  of 

the  periosteum ;  it  is  known  aa  the  periosteum  internum,  endosteum,  or 
membrana  medullaris. 

Compact  Bone. — Compact  bone,  such  as  that  composing  the  shafts 
of  the  long  bones,  consists  of  concentric  lamellae  of  calcified  fibrous  tissue 
which  constitute  the  Haversian  systems.,  together  with  groups  of  parallel 
lamina,  which  are  interposed  between  adjacent  Haversian  systems  and 
are  known  as  the  interstitial  or  ground  lamellae.  Many  of  the  interstitial 
lamellae  are  the  .remains  of  Haversian  systems  which  have  been  partially 


FIG.  87. — LONGITUDINAL  SECTION  OP 
GROUND  BONE  FROM  THE  SHAFT  OF 
THE  HUMAN  FEMUR. 

a,  Haversian  canals;  b,  lacunae;  c, 
canaliculi.     X  100.    (After  Kolliker.) 


BONE 


75 


FIG.  88. — ISOLATED  BONE  CELL, 
SHRUNK  AWAY  FROM  WALL 
OF  LACUNA  AT  I. 

(Schafer,  after  Joseph.) 


absorbed  during  the  development  of  the  bone.  In  a  section  through 
the  shaft  of  a  long  bone  the  Haversian  systems  are  found  in  the  middle  of 
the  wall,  while  superficial  to  them  and  just  within  the  periosteum  are  a 
number  of  lamellae  which  may  be  traced 
much  or  all  of  the  way  around  the  cir- 
cumference of  the  cylindrical  shaft,  and 
which  are  known  as  the  external  circum- 
ferential or  periosteal  lamellae.  On  the 
inner  surface  of  the  compact  bony  wall  is 
a  similar  group  of  parallel  laminae  which 
adjoin  the  marrow  cavity,  and  are  known 
as  the  internal  circumferential  or  endos- 
teal  lamellce.  In  their  finer  structure 
the  circumferential  lamellae  are  exactly 
similar  to  the  cylindrical  bony  lamella?  of 
the  Haversian  systems. 

HAVERSIAN  SYSTEM. — A  Haversian  system  contains  a  small  central 
canal  (0.05-0.1  mm.  dia.),  which  is  occupied  by  connective  tissue,  marrow 
cells  derived  from  the  marrow  cavity  during  the  process  of  development, 

small  blood-vessels,  nerve  fibers,  and 
perivascular  lymphatics.  Concen- 
trically arranged  around  the  Haver- 
sian canal  are  parallel  layers  of 
dense  fibrous  tissue,  the  Haversian 
lamellce.  The  fiber  bundles  of  this 
tissue  form  an  interlacing  network 
whose  bundles  frequently  cross  each 
other  at  right  angles  and  whose  in- 
terstices are  occupied  by  a  solid  cal- 
careous mass,  consisting  chiefly  of 
the  phosphates  (about  80  per  cent.) 
and  carbonates  of  calcium.  From 
four  to  twenty  such  calcareous  lam- 
ellae are  found  in  each  Haversian 
system.  The  organic  substance  of 

bone  consists  chemically  of  collagen,  osseomucoid  and  small  amounts  of 
other  albumiroid  bodies. 

Both  in  and  between  the  lamellae  are  many  small  ovoid  spaces  which 
are  partially  filled  by  small  flattened  cells,  the  bone  cells;  these  spaces 
are  known  as  the  lacunae.  From  each  lacuna  minute  canals,  the  canaliculi, 


FIG.  89. — AN  HAVERSIAN  SYSTEM, 
INCLUDING  THE  CENTRAL  CANAL, 
SEVERAL  LAMELLA,  LACUN/E  AND 
CANALICULI. 


76 


CONNECTIVE  TISSUE— CAETILAGE— BONE 


radiate  in  all  directions,  thus  placing  the  lacuna  in  open  communication 
with  its  neighbors,  and  eventually  with  the  lymph  spaces  of  the  cen- 
tral Haversian  canal.  The  branching  processes  of  the  bone  cells  fre- 
quently project  for  a  short  distance  into  the  canaliculi.  These  cyto- 
plasmic  branches  are  more  numerous  in  newly  formed  bone,  later  they 
are  retracted  and  the  cells  become  more  or  less  shriveled  in  appearance. 
The  Haversian  system,  being  developed  about  a  central  canal  which 
marks  the  course  of  a  blood-vessel,  necessarily  acquires  a  slender  columnar 
shape,  its  long  axis  being  usually  disposed  in  a  direction  nearly  parallel 
to  that  of  the  bone  of  which  it  forms  a  part.  The  Haversian  canals  fre- 
quently branch  to  permit  a  corre- 
sponding division  of  their  blood-ves- 
sels, and  all  of  the  Haversian  canals 
are  connected  either  directly  or  indi- 
rectly with  the  periosteum,  the  nu- 
trient foramina,  or  the  marrow  cavity 
— thus  forming  a  complete  connected 
system  between  marrow  cavity  and 
surface — from  the  blood-vessels  of 
which  -their  vascular  supply  is  de- 
rived. 

INTERSTITIAL  LAMELLAE. — The  in- 
terstitial lamellae  are  likewise  com- 
posed of  dense  interlacing  bundles  of 
calcined  fibrous  tissue,  within  and  be- 
tween which  are  lacunae,  canaliculi, 
and  bone  cells,  all  disposed  in  a  man- 
ner exactly  similar  to  their  arrangement  within  the  concentric  lamellse 
of  the  Haversian  systems.  Coursing  through  the  interstitial  and  circum- 
ferential lamellae  are  Vollcmanns  canals,  which  are  similar  in  origin,  con- 
tents, and  function  to  the  Haversian  canals  but  which  are  not  surrounded 
by  concentric  lamellae.  Volkmann's  canals  frequently  arise  as  branches  of 
the  Haversian  canals  which  wander  out,  as  it  were,  into  the  interstitial 
lamellae. 

CIRCUMFERENTIAL  LAMELLA;. — The  circumferential  lamellae  do  not 
differ  in  structure  from  the  other  osseous  lamellae.  They  possess  the 
same  arrangement  of  laminated  calcareous  connective  tissue,  with  lacunae, 
canaliculi,  and  bone  cells,  as  in  the  concentric  and  interstitial  lamellae. 
Even  more  than  elsewhere,  however,  the  outer  circumferential  lamellae  are 
firmly  bound  together  by  collagenous  and  elastic  fibers  which  pass  from 


FIG.   90. — TRANSVERSE  SECTION  OP 
HAVERSIAN  CANAL,  WITH  CONTENTS. 

a,  arteriole;  v,  venule;  I,  lymphatic; 
n,  non-medullated  nerve  fibers;  c, 
bone  cell.  (After  Schafer.) 


BONE  77 

the  periosteum  into  and  through  the  superficial  lamella? ;  these  are  known 
as  the  perforating  fibers  of  Sharpey.  Similar  fibers  connect  together  the 
concentric  and  interstitial  lamellae.  The  perforating  elastic  fibers  are 
frequently  surrounded  by  an  envelope  of  fibrous  connective  tissue. 

Bone  Marrow. — Bone  marrow  consists  of  a  variety  of  connective 
tissue,  largely  reticular,  which  is  rich  in  fat  cells  and  blood-vessels  and 
which  also  contains  osteogenic  and  hemogenic  elements,  the  marrow 
cells  or  myelocytes.  According  to  the  relative  proportion  of  these  ele- 
ments marrow  is  said  to  present  two  types,  the  yellow  and  the  red  marrow. 
The  yellow  marrow  consists  almost  entirely  of  fat,  with  only  occasional 
bands  of  true  marrow  tissue.  The  red  marrow  contains  very  little  fat, 
bub  is  so  abundantly  supplied  with  blood  and  marrow  cells  as  to  closely 
resemble  a  very  vascular  lymphoid  tissue.  The  embryonic  medulla  of  all 
bones  contains  fetal  red  marrow,  but  in  later  life  the  larger  masses  in 
the  medulla  of  the  shafts  of  the  long  bones  are,  in  man,  changed  to  the 
yellow  variety.  The  red  marrow,  however,  persists  in  the  epiphyses  of 
the  long  bones  and  in  cancellous  bone  generally;  it  is  especially  charac- 
teristic of  the  marrow  cavities  of  the  ribs,  vertebrae,  base  of  the  skull,  and 
sternum.  It  is  the  source  of  supply  of  blood-cells  in  the  adult. 

BED  MARROW. — Eed  marrow  consists  of  fibrous  and  reticular  tissues 
which  are  infiltrated  by  marrow  cells  and  richly  supplied  with  small 
blood-vessels.  The  smaller  veins  possess  exceedingly  thin  walls,  readily 
pervious  to  the  blood-cells.  The  walls  are  so  delicate  that  it  becomes 
very  difficult  to  determine  with  certainty  whether  or  not  their  eiidothe- 
lium,  as  also  that  of  the  capillaries,  may  be  occasionally  absent,  thus 
placing  the  blood-stream  in  direct  communication  with  the  pulp  of  the 
bone  marrow. 

The  hemogenic  elements  of  marrow  will  be  described  under  the 
subject  of  blood  development,  where  red  marrow  must  again  be  con- 
sidered. At  this  point  it  is  only  necessary  to  describe  the  osteogenic 
elements.  These  are  (1)  the  osteoblasts,  or  bone  builders,  and  (2)  the 
osteoclasts,  or  bone  destroyers.  The  osteogenic  process  as  a  whole  is  of 
course  dependent  upon  the  blood,  with  all  its  hemal  elements. 

OSTEOBLASTS. — These  are  cells  which  may  assume  various  shapes 
depending  upon  their  spatial  relationship  to  the  bony  substance.  When 
free  they  are  of  round  or  slightly  oval  shape;  lining  the  marrow  cavity 
or  covering  the  bone  as  portions  of  the  periosteum  or  applied  to  spicules 
of  cancellous  bone  they  may  become  considerably  flattened.  The  nucleus 
is  generally  round  or  oval,  deeply  chromatic  and  granular.  As  spheroidal 
cells  they  have  an  average  diameter  of  about  8  microns.  They  are  with 


78  CONNECTIVE  TISSUE— CAKTILAGE— BONE 

difficulty  distinguished  from  lymphocytes  except  when  characteristically 
arranged  as  a  membranous  coat  upon  the  surface  of  bony  walls  or  spic- 
ules.  They  become  the  bone  cells  of  compact  bone.  Osteoblasts  and  lympho- 
cytes are  genetically  closely  related,  both  being  relatively  slightly  differen- 
tiated mesenchymal  cells.  In  the  bone  marrow  of  the  turtle  osteoblasts 
may  differentiate  into  leukocytes.  It  seems  probable  that  persistent  fetal 
osteoblasts  of  adult  red  marrow  may  function  as  parent  blood-cells. 

OSTEOCLASTS. — These  are  giant  multinuclear  cells,  often  containing 
as  many  as  ten  to  twenty  or  more  nuclei.  They  are  the  cells  by  whose 
agency  bone  is  destroyed  during  the  processes  of  development  and  growth. 
They  are  similar  to,  but  not  identical  with,  the  polykaryocytes  of  hemo- 
genic  foci  which  are  concerned  with  the  process  of  blood-cell  formation. 
The  osteoclasts  originate  by  a  process  of  fusion  of  reticular  cells  of  the 
marrow;  the  hemogenic  polykaryocytes  originate  from  lymphocytes 
(hemoblasts)  by  repeated  amitotic  division  of  the  nucleus. 

Blood  Supply. — Marrow,  and  especially  the  red  variety,  is  richly 
supplied  with  blood.  The  nutrient  or  medullary  artery  penetrates 
obliquely  through  the  nutrient  foramen  to  the  marrow  cavity  of  a  long 
bone  where  it  divides  into  an  ascending  and  descending  branch  and 
supplies  an  abundance  of  small  arteries  to  all  portions  of  the  medulla. 
The  terminal  arteries  end  in  broad  capillary  vessels  whose  wide  lumen 
and  delicate  endothelial  walls  determine  their  character  as  sinusoids.  It 
was  formerly  thought  that  the  endothelial  walls  of  these  vessels  were  here 
and  there  deficient,  and  although  recent  investigations  discredit  the 
former  observations,  the  all-important  fact  remains  that  the  endothelial 
walls  are  pervious  to  both  red  and  white  blood-cells.  Certain  of  the  ter- 
minal arteries  anastomose  with  those  of  the  cancellous  epiphyses,  and 
with  the  arteries  which  enter  the  Haversian  canals  of  the  compact  bone 
from  the  periosteum. 

Efferent  veins  return  the  blood  from  the  sinusoidal  capillaries  of  the 
marrow.  These  veins,  passing  as  companion  veins  to  the  medullary 
artery  through  the  nutrient  foramen,  or  independently  through  separate 
foramina,  as  also  those  of  the  bony  tissue,  are  not  supplied  with  valves. 
Outside  of  the  bones,  however,  these  same  veins  contain  abundant  valves. 

The  Lymphatics. — The  lymphatics  of  bone  occur  in  great  abundance 
in  the  periosteum,  and  as  perivascular  spaces  penetrate  the  canals  of 
Havers  and  Volkmann  and  thus  reach  the  medullary  cavity.  The  exist- 
ence of  lymphatics  within  the  marrow,  other  than  in  the  sheaths  of  the 
blood-vessels,  is  doubtful. 

The  Nerves. — The  nerves  accompany  the  blood-vessels  in  all  portions 


BONE  79 

of  the  bone  and  marrow  and  form  a  rich  perivascular  plexus  which  is 
distributed  to  the  walls  of  the  vessels ;  occasional  side  fibrils  are  also  dis- 
tributed to  the  marrow.  Nerve  endings  have  not  been  demonstrated  in 
compact  bone  nor  in  the  articular  cartilages.  In  the  periosteum  terminal 
nerve  fibrils  are  supplied  to  the  musculature  of  the  blood-vessels,  and 
other  sensory  fibrils  end  in  lamellar  corpuscles. 

Development  of  Bone — Bone  tissue  makes  its  appearance  relatively 
late  in  fetal  life.  The  long  bones  are  first  mapped  out  by  masses  of 
hyaline  cartilage.  The  entire  skeleton,  with  the  exception  of  the  flat 
bones  of  the  face  and  those  of  the  vault  of  the  skull,  is  thus  primarily 
formed  by  plates  of  fetal  cartilage.  The  process  by  which  these  cartilag- 
inous plates  are  transformed  into  bone  is  known  as  intracartilaginous  or 
enchondral  ossification.  The  process  is  essentially  one  of  replacement 
of  cartilage  by  bone,  not  one  of  change  of  cartilage  into  bone.  The 
resulting  bones  are  known  as  substitution  bones. 

The  flat  bones  of  the  face  and  skull  (including  the  interparietals, 
parietals,  frontals,  squamosals,  tympanics,  median  pterygoid  plate  of  the 
sphenoid,  nasals,  lacrimals,  malars,  palatine,  vomer,  maxilla,  and  a 
portion  of  the  mandible)  are  formed  directly  from  the  mesenchymal 
blastema  without  the  intervention  of  cartilage.  This  method  of  bone 
formation  differs  somewhat  from  the  above  and  is  known  as  intramem- 
Iranous  ossification. 

INTRACARTILAGINOUS  OSSIFICATION. — This  process  begins  with  the 
formation  of  plates  of  hyaline  cartilage  whose  shape  corresponds  more  or 
less  closely  with  that  of  the  future  bone.  This  type  of  fetal  cartilage 
differs  from  the  hyaline  cartilage  of  the  adult  only  in  the  irregular  form 
and  distribution  and  greater  abundance  of  its  cartilage  cells. 

Each  plate  of  fetal  cartilage  is  enveloped  by  a  layer  of  embryonal 
fibrous  tissue,  the  fetal  perichondrium.  The  outer  portion  of  the  fibro- 
cellular  layer  is  destined  to  become  the  periosteum  of  the  future  bone; 
its  innermost  portion  contains  many  small  round  cells,  which  from  their 
intimate  relation  to  bone  production,  are  known  as  osteoblasts.  The 
inner  portion  of  the  perichondrium  forms  the  osteogemc  layer  of  the 
future  periosteum. 

Centers  of  Ossification. — Ossification  of  the  cartilage  begins  at  one  or 
more  points  which  are  called  centers  of  ossification.  In  the  long  bones, 
in  which  the  process  of  bone  formation  can  be  most  readily  traced,  there 
are  usually  three  such  centers,  one  near  the  middle  of  the  cartilaginous 
plate,  from  which  the  diaphysis  is  formed,  and  one  epiphysial  center  at 
each  extremity.  The  centers  for  the  epiphyses  make  their  appearance 


SO  CONNECTIVE  TISSUE— CARTILAGE— BONE 

much  later  than  that  for  the  shaft  of  the  bone,  for  the  most  part  not 
until  some  mouths  after  birth,  and  from  an  extension  of  marrow  from 
the  primary  center. 

Enlargement  of  the  Cartilage  Cells. — The  first  indication  of  begin- 
ning bone  formation  is  evidenced  by  an  enlargement  of  the  cartilage  cells 
which  promptly  arrange  themselves  in  rows  or  columns  that  radiate  from 
the  center  of  ossification  (calcification).  This  process  is  accompanied 
by  absorption  of  the  adjacent  cartilage  matrix,  so  that  the  enlarged  car- 

C 


FIG.  91. — THE  PRIMARY  CHANGES  IN  INTRACARTILAGINOUS  BONE  FORMATION. 

A,  metatarsus;  B  and  C,  phalanges  of  human  fetus.  In  A,  the  earliest  enlarge- 
ment of  cartilage  cells  at  the  center  of  ossification  is  shown.  B  and  C  are  successively 
later  stages.  The  bones  are  cut  in  longitudinal  section.  Carmin  hematoxylin  stain. 
X  27.  (After  Toldt.) 

tilage  cells  are  contained  within  broad  spaces  or  areolce.  The  cartilage 
cells  now  appear  to  undergo  a  gradual  but  progressive  absorption ;  their 
cytoplasm  becomes  shrunken  and  granular  and  finally  disappears,  even 
the  nucleus  at  last  succumbs  to  the  process. 

Calcified  Cartilage. — The  absorption  of  the  cartilaginous  matrix  pro- 
ceeds more  rapidly  in  those  portions  which  separate  the  individual  cells 
in  the  columns  than  in  those  other  portions  which  intervene  between 
the  adjacent  rows  of  cartilage  cells.  While  the  former  portions  are 
entirely  absorbed,  remnants  of  the  latter  remain,  and  in  them  calcium 
salts  are  deposited  in  an  irregular  manner.  Calcified  cartilage,  the  most 
primitive  of  the  calcareous  tissues,  is  thus  formed. 


FIG.  92.— A  LONGITUDINAL  SECTION  OF  THE  Two  DISTAL  PHALANGES  FROM  THE 
FINGER  OF  A  FIVE-MONTHS'  HUMAN  FETUS. 

Kn,  cartilage  showing  calcification  and  resorption;    ek,  enchondral  bone;  M, 
marrow  cavity;  pk,  periosteal  bone.      X  15.    (From  Sabotta's  "Histology.") 

81 


CONNECTIVE  TISSUE— CAETILAGE— BONE 


tear.  c. 


Primordial  Mar- 
row Cavities. — The 
absorption  of  the 
cartilage  matrix  re- 
sults in  the  forma- 
tion of  broad  spaces 
into  which  osteo- 
genic buds  of  prim- 
itive marrow  tissue 
push  their  way  from 
the  perichondrium. 
Thus  the  primordial 
marrow  cavities  are 
formed.  The  fetal 
marrow  which  now 
occupies  these  cav- 
ities is  derived  from 
the  osteogenic  layer 
of  the  primitive  peri- 
osteum. The  oste- 
ogenous  tissue  of  this 
layer,  containing  os- 
teoblasts,  osteoclasts, 
and  developing 
blood-vessels,  grows 
into  the  cartilage  in 
the  form  of  budlike 
cords  which  are  pre- 
ceded by  absorption 
of  the  adjacent  car- 
tilage matrix.  This 
so-called  'eruptive 
tissue  '  promptly 
reaches  the  center  of 
ossification  and  bur- 
rows its  way  into  the 
enlarged  cartilage 
lacunas  whose  cells  are  now  replaced  by  primary  osteogenic  marrow.  The 
destruction  of  cartilage  is  initiated  and  maintained  by  agency  of  the 
osteogenic  tissue,  presumably  through  specific  cells,  the  so-called  chon- 


--gi.  c. 


FIG.  93. — RECONSTRUCTION  OF  CARTILAGE  INTO  BONE. 

car.  c.,  cartilage  cells  in  successive  stages  of  degenera- 
tion; ost,  osteoblasts;  gi.  c.,  giant  cells  (osteoclasts);  b, 
young  bone;  bl.  c.,  blood  cells.  (From  Dahlgren  and 
Kepner.) 


BONE 


drodasts,  the  morphological  marks  of  identification  of  which  are  not  yet 
known.  According  to  some  investigators  (e.g.,  Retterer,  1900)  the  car- 
tilage cells  do  not  disintegrate  but  pass  into  the  marrow  cavity  where 
they  become  osteoblasts. 

Primary  Bone. — The  osteoblasts  which  thus  gain  access  to  the  pri- 
mary marrow  cavities,  now  arrange  themselves  along  the  surface  of  the 
remnants  of  calcified  cartilage  and 
begin  the  deposit  at  their  proximal 
surface  of  the  fibrous  tissue  and 
calcareous  salts  which  compose  the 
primary  bone.  The  osseous  matrix 
is  commonly  assumed  to  be  the 
product  of  a  transformation  of  the 
exoplasm  of  the  osteoblasts.  Many 
of  the  osteoblasts  apparently  be- 
come entangled  in  this  newly 
formed  tissue  and  form  the  bone 
cells.  The  fetal  cartilage  is  thus 
transformed  into  a  spongy  mass  of 
primary  osseous  tissue  whose  spic- 
ules  are  formed  by  a  core  of  calci- 
fied cartilage  upon  which  are  de- 
posited successive  layers  of  bony 
tissue  with  their  included  Iacuna3 
and  bone  cells.  In  sections  stained 
with  hematoxylin  and  eosin,  the 
central  strand  of  calcified  cartilage 
is  colored  blue,  the  primary  bone, 
red. 

Axial  sections  of  long  bones  at 
this  stage  of  ossification  show  all 
the  above  changes  in  regular  suc- 
cession from  the  fetal  hyaline  car- 
tilage at  the  extremities  to  the  primary  bone  with  its  marrow  cavities  in 
the  center.  The  process  of  ossification  steadily  progresses  toward  the  ends 
of  the  bone,  the  line  of  enlarged  cartilage  cells  constantly  advancing 
farther  and  farther  from  the  original  center  of  ossification. 

Absorption  of  the  Newly  Formed  Bone. — It  is  at  this  stage,  however, 
that  the  giant  cell  osteoclasts  become  most  active  and  the  absorption  of 
the  newly  formed  bone  progresses  rapidly.  The  osteoclasts  collect  along 


FIG.     94. — TRABECULA     OF     PRIMARY 
ENCHONDRAL     BONE,     SHOWING     A 
CENTRAL    DEEP-STAINING    CORE    OP 
CALCIFIED   CARTILAGE   AND    A    PER- 
IPHERAL LAYER  OF  OSTEOBLASTS. 
Osteoblasts  have   become   incorpora- 
ted within  the  bone  as  bone  cells.    From 
the  finger  of  a  human  fetus. 


84 


CONNECTIVE  TISSUE— CARTILAGE— BONE 


the  surface  of  the  spiculcs  of  primary  bone  in  considerable  numbers  and 
appear  to  sink  into  little  recesses  which  they  form  within  the  bony 
tissue.  The  little  bays  which  are  thus  formed  in  the  primary  bone  are 
the  lacuna  of  Howsliip.  The  continued  absorption  soon  breaks  down 
and  removes  the  trabeculas  and  partitions  of  spongy  bone  and  forms  a 
central  medullary  cavity  of  constantly  increasing  size. 

Perichondrial  Ossification. — Coincident  with  these  changes  within  the 
cartilage  the  osteogenic  tissue  which  forms  the  inner  layer  of  the  peri- 

chondrium  produces  succes- 
sive layers  of  bony  tissue 
upon  the  surface  of  the  fetal 
cartilage.  This  process  of 
perichondrial  (periosteal) 
ossification  proceeds  in  a 
manner  similar  to  that  by 
which  bone  is  formed  in 
membrane  which  is  not 
closely  applied  to  cartilage. 
Perichondrial  bone  for- 
mation is  essentially  of  the 
intramembranous  type.  In 
essence  there  is  no  valid  dis- 
tinction between  endochon- 
dral,  perichondrial  a  n  d 
membrane  bone  develop- 
ment, since  each  involves 
calcification  of  a  fibrillar 
matrix  by  agency  of  the 
same  cell,  the  osteoblast.  At 
irregular  intervals  the  osteo- 
clasts  collect  and  the  pri- 
mary perichondrial  bone  is 

absorbed.  Into  these  cavities  buds  of  vascular  osteogenic  tissue  push 
their  way  to  form  canals  of  considerable  length.  Upon  the  surface  of  the 
canals  which  are  thus  hollowed  out  of  the  perichondrial  bone,  the  Haver- 
sian  spaces,  the  osteoblasts  deposit  successive  concentric  layers  of  bony 
tissue  and  the  Haversian  systems  make  their  appearance.  Finally,  upon 
the  surface  of  the  periosteal  bone  successive  layers  of  newly  formed  bony 
tissue  compose  the  external  circumferential  lamella;,,  while  upon  the 
wall  of  the  medullary  cavity  a  similar  endosteal  layer  of  bone-forming 


FIG.  95. — TRABECTTLA  OF  PRIMARY  BONE  FROM 
THE  FINGER  OF  A  HUMAN  FETUS. 

Three  giant  cells  (osteoclasts)  are  shown  at 
the  right,  two  resting  in  Howship's  lacunae. 


BONE  85 

cells  deposits  the  internal  circumferential  lamella.  The  Haversian  canals 
are  actually  continuations  of  the  marrow  cavity,  and  the  larger  are  even 
lined  by  endosteum. 

With  the  formation  of  the  perichondrial  bone  the  lateral  expansion 
of  the  organ  by  endochondral  bone  formation  necessarily  ceases.  Hence- 
forth increase  in  diameter  of  the  bone  is  only  produced  by  continued 
absorption  internally  of  the  compact  bony  wall  and  the  formation  of  new 
bone  beneath  the  periosteum  by  frequent  repetitions  of  the  processes  of 
periosteal  (perichondrial)  ossification  as  already  described.  The  rem- 
nants of  those  Haversian  and  circumferential  lamellae  which  are  only 
partially  absorbed  in  this  process  form  the  interstitial  lamella  of  the  ma- 
ture bone.  In  the  long  bones  and  in  flat  cartilage  bones  ossification  at 
first  proceeds  in  the  perichondrium,  endochondral  ossification  appearing 
only  later ;  in  the  short  bones  ossification  is  endochondral  until  the  carti- 
lage is  entirely  replaced  by  bone. 

Epiphytal  Ossification. — During  the  processes  of  endochondral  and 
perichondrial  ossification  within  the  shaft  of  the  bone,  the  epiphysial 
cartilages  continue  to  grow.  Finally,  however,  ossification  begins  in  the 
epipliysis,  osteogenic  tissue  having  pushed  in  from  the  primary  center  of 
the  diaphysis,  and  proceeding  in  the  same  manner  as  in  the  shaft, 
results  in  the  formation  of  primary  spongy  bone,  some  of  which  is  ab- 
sorbed and  replaced  by  more  compact  bony  tissue,  as  occurs  in  the  wall 
of  the  diaphysis.  In  its  central  portions  the  tissue  retains  its  spongy 
arrangement  and  but  few  Haversian  systems  are  formed.  It  is  thus 
that  the  cancellous  bone  of  this  part,  as  also  of  the  ends  of  the  diaphysis, 
is  formed. 

At  the  point  where  the  expanding  centers  of  ossification  of  the  shaft 
and  epiphysis  are  about  to  meet,  a  line  of  unossified  cartilage,  the 
epiphysial  line,  persists  until  growth  of  the  bone  is  complete.  It  is  by 
growth  of  this  cartilaginous  disk,  with  continued  formation  of  cartilage 
mainly  on  its  inner  surface,  and  its  concomitant  replacement  by  bone, 
that  the  bone  increases  its  length.  After  ossification  of  this  epiphysial 
synchondrosis  at  about  the  twenty-first  year,  growth  in  length  must 
cease.  Meanwhile  the  perichondrium  has  become  periosteum. 

The  following  is  a  resume  of  the  various  stages  of  endochondral  ossifi- 
cation : 

1.  Formation  of  the  fetal  hyaline  cartilages  from  precartilage  mesen- 

chyme  blastema. 

2.  Enlargement  of  the  cartilage  cells  with  a  rearrangement  into 

radiating  cell  rows  at  the  center  of  ossification. 
7 


86  CONNECTIVE  TISSUE— CARTILAGE— BONE 

3.  Absorption  of  the  cartilage  matrix  between  the  cells  of  the  rows 

and  finally  also  of  the  cells  themselves.  Calcification  of  per- 
sistent remnants  of  cartilage  matrix  between  the  rows  of 
cells. 

4.  Eruption  of  the  subperiosteal  osteogenic  tissue,  invasion  to  center 

of  cartilage  plate,  and  the  formation  of  primary  marrow  cavi- 
ties at  the  center  of  ossification. 

5.  Gradual  extension  of  the  above  processes  followed  by  a  deposit 

of  primary  bone  by  the  osteoblasts  upon  the  calcified  cartilage 
spicules.  Coincident  osteoblastic  deposit  of  perichondrial  bone 
beneath  and  within  the  perichondrium  of  the  cartilage  plate. 

6.  Absorption  of  portions  of  the  primary  bone  by  the  osteoclasts  to 

form  the  large  central  marrow  cavity  or  medulla.  The  ab- 
sorption involves  both  the  endochondral  and  the  perichondrial 
bone  and  is  accompanied  by  a  further  deposit  of  new  bone 
at  the  periphery.  In  the  perichondrial  bone  cylindrical  axial 
channels  are  formed,  in  which  the  deposit  of  new  bone  pro- 
duces the  Haversian  systems  of  the  compact  bony  tissue. 

INTRAMEMBRAXOCS  OSSIFICATIOX. — This  is  the  simpler  and  more 
direct  method  of  bone  formation.  In  principle  it  is  identical  with  peri- 
chondrial ossification.  Endochondral  bone  development  differs  from  it 
only  in  respect  of  the  additional  processes  involved  in  the  removal  and 
replacement  of  the  hyaline  cartilage. 

Membrane  bones,  including  the  flat  bones  of  the  face  and  the  vault  of 
the  cranium,  arise  directly  in  the  meseuchyma.  The  first  indication  of 
ossification  is  the  enlargement  and  rounding  up  of  a  group  (or  groups) 
of  mesenchyme  cells,  and  their  association  in  the  form  of  an  irregular 
membrane.  Among  the  cells  appear  bundles  of  delicate  collagenous 
fibrils,  the  osteogenic  fibers  (Sharpey),  radiating  beyond  the  limits  of 
the  cell  group.  The  cells  of  this  initial  ossific  group  begin  to  function 
as  osteoblasts  and  deposit  osseous  matrix  among  the  fiber  bundles. 
This  original  osseous  trabecula  marks  approximately  the  center  of  the 
future  bone.  The  surrounding  loose  mesenchyma  has  meanwhile  become 
increasingly  vascular.  Vaguely  outlining  the  peripheral  limits  of  the 
definitive  bone  appears  a  relatively  thick  layer  of  denser,  more  cellular 
mesenchyma,  the  cells  in  general  maintaining  a  fusiform  shape.  This 
represents  the  primitive  periosteum  of  the  forming  bone.  The  bone  takes 
shape  internally  by  the  appearance  of  numerous  trabecula?,  which  arise 
in  the  manner  described  for  the  initial  spicules  and  then  unite  into  a 


BONE  87 

bony  sponge-like  structure  enclosing  vascular  mesenchyma,  the  primary 
marrow.  The  spicules  of  the  cancellous  bone  contain  numerous  bone  cells 
— the  representatives  of  original  osteoblasts  which  have  become  enmeshed 
in  their  own  product  of  osseous  matrix — and  are  covered  with  an  epithe- 
lioid  membrane  of  a  single  or  double  layer  of  osteoblasts,  which  contribute 


FIG.  96. — INTRAMEMBRANOUS  BONE  FORMATION  IN  THE  LOWER  JAW  OF  A  SHEEP 

FETUS. 

a,  bone;  b,  primary  marrow  cavity;  c,  osteoblasts;  d,  growing  point  of  the  primitive 
bone,  beyond  which  primary  marrow  is  developing  in  the  connective  tissue  of  the 
mesoblast.  X  300.  (After  Bohm  and  von  Davidoff.) 

to  the  further  growth  of  the  bony  trabeculac.  The  marrow  includes 
besides  osteoblasts  and  the  specific  marrow  cells — somewhat  less  numerous 
than  in  the  primary  marrow  of  endochondral  bone — numerous  osteoclasts 
under  whose  absorptive  agency,  assisted  by  the  productive  activity  of 
the  osteoblasts,  the  inner  conformation  of  the  growing  bone  continually 
alters  its  details.  Peripheral  osteoblasts,  arising  from  the  inner  layer 
of  the  periosteum,  produce  the  more  compact  external  plates  of  the  bone. 


88  CONNECTIVE  TISSUE— CARTILAGE— BONE 

In  the  flat  bones  of  the  skull,  the  central  cancellous  bone  is  designated 
diploe,  the  peripheral  compact  bone,  tables.  Membrane  bones  may  con- 
tain typical  Haversian  systems  (Arey,  Anat.  Rec.,  17,  1,  1919). 

The  conditions  which  determine  that  certain  bones  may  arise  directly 
in  mesenchyma  while  others  must  pass  through  a  cartilaginous  stage  are 
obscure. 

It  is  commonly  believed  that  periosteum  is  essential  for  bone  regenera- 
tion, and  its  preservation  is  aimed  at  where  new  growth  is  desired  after 
osteotomy.  But  according  to  W.  Macewen  ("The  Growth  of  Bone," 
Maclehose  &  Sons,  Glasgow,  1912),  who  has  made  a  comprehensive  ex- 
perimental study  of  osteogenesis  in  regenerating  bone  in  dogs,  the  perios- 
teum functions  simply  as  a  confining,  nutritive,  and  protective  membrane, 
but  has  no  osteogenic  significance.  His  observations  lead  him  to  conclude 
also  that  in  the  long  bones  the  osteoblasts  are  derived  from  proliferating 
cartilage  nuclei  freed  from  the  disappearing  matrix.  Under  more  favor- 
able conditions  regeneration  is  said  to  occur  through  direct  osteoblastic 
activity,  under  less  favorable  conditions  a  cartilaginous  transition  stage 
intervenes.  He  deduces  from  his  experiments  that  "diaphyseal  bone  is  re- 
produced by  proliferation  of  osteoblasts  derived  from  preexisting  osseous 
tissue,  and  that  its  regeneration  takes  place  independently  of  the  perios- 
teum/' The  periosteum  is  conceived  as  being  an  important  factor  in  de- 
termining the  conformation  and  growth  limit  of  bone. 


JOINTS 

Joints  are  divisible  into  two  main  types,  the  movable  and  the  'im- 
movable/ or  (1)  diarthroses  and  (2)  synarthroses.  These  and  their 
several  modifications  call  for  histologic  description.  Synarthroses  include 

(a)  syndesmoses,  or  joints  in  which  the  connecting  substance  is  a  dense 
fibro-elastic  tissue  joining  the  bones  immovably  as  in  the  articulation  of 
the  skull  (sutura),  or  where  it  consists  of  ligamentous  tissue  permitting 
slight  movement  as  between  the  lower  ends  of  the  tibia  and  fibula ;  and 

(b)  synchondroses,  in   which  the   connection   is  effected  by   cartilage, 
either  hyaline  (e.g.,  between  the  epiphyses  and  diaphysis  of  young  bones) 
or  fibrous  (e.g.,  the  inter  vertebral  disks  of  the  vertebral  column). 

In  relation  with  diarthroses  are  in  several  instances  (mandibular, 
lower  radio-ulnar,  costosternal,  sternoclavicular,  acromioclavicular) 
mtra-articular  menisci  of  fibrocartilage ;  here  the  articular  cartilages  of 
the  bones  concerned  are  also  of  the  fibrous  variety.  The  semilunar  car- 
tilages of  the  knee  and  the  glenoid  cartilage  of  the  shoulder  joint  are  also 


JOINTS  8D 

of  the  fibrous  type.  These  cartilages  serve  to  deepen  the  sockets  in  which 
the  respective  ends  of  the  femur  and  humerus  move  and  are  known  as 
adaptation  cartilages  or  labra  glenoidalia. 

The  joint  cavity  of  a  diarthrosis  is  enveloped  in  a  capsule  consisting 
of  two  layers,  an  outer  fibre-elastic  continuous  with  the  periosteum  and 
an  inner  cellular  layer,  the  synovial  membrane,  consisting  of  epithelioid 
cells  forming  a  mesenchymal  epithelium.  The  function  of  the  synovial 
membrane  is  to  secrete  a  lubricating  fluid,  the  synovia,  consisting  of  about 
94  per  cent,  water  with  small  amounts  of  mucoid  substances  and  oil. 
In  the  large  joints  the  synovial  (serous)  membrane  is  thrown  into  villus- 
like  folds  (Fig.  240).  The  covering  cellular  membrane  is  occasionally 
imperfect;  the  cells  vary  from  the  flattened,  typical  mesothelial  cells,  to 
the  cubic  variety  (Fig.  44),  and  rest  directly  upon  a  vascular,  frequently 
fatty,  fibrous  stroma. 


CHAPTER   IV 

MUSCULAR   TISSUE 

GENERAL    CONSIDERATIONS 

Muscular  tissue  consists  essentially  of  protoplasm  in  which  the  gen- 
eral vital  property  of  contractility  has  become  predominant.  However, 
the  path  of  contraction  is  practically  limited  to  one  direction,  the  long 
axis  of  the  cell.  This  phenomenon  of  contractility  results  from  the  dif- 
ferentiation of  specially  contractile  fibrils,  the  myofibrils,  from  the  pro- 
toplasm of  embryonic  muscle  elements,  the  myoblasts.  The  protoplasm 
of  the  muscular  tissue  is  called  sarcoplasm.  Adult  muscular  tissue  may 
be  divided  into  three  classes:  smooth,  cardiac,  and  striped.  All  three 
types  arise  from  mesoderm,  with  the  exception  of  the  dilator  and  sphinc- 
ter muscles  of  the  iris  of  the  eye,  and  the  muscle  of  the  secretory  portion 
of  the  sweat  gland — both  of  the  smooth  variety — which  are  generally  be- 
lieved to  be  of  ectodermal  origin.  In  lower  forms,  muscle  tissue  may  be 
largely  derived  from  the  ectoderm  and  even  from  the  entoderm. 

The  smooth  muscle  is  in  general  limited  to  the  viscera ;  it  is  not  under 
the  control  of  the  will,  hence  also  called  involuntary  muscle.  The  cardiac 
type  is  limited  to  the  heart,  and  to  the  middle  layer  of  the  roots  of  the 
aorta,  pulmonary  artery,  and  pulmonary  veins.  It  is  striped,  but  like 
smooth  muscle,  controlled  by  the  sympathetic  nervous  system;  therefore 
independent  of  the  will,  hence  also  of  involuntary  type.  So-called  striped 
or  skeletal  muscle  is  practically  limited  to  the  skeleton,  and  subserves  the 
function  of  skeletal  movement.  This  group  includes  also  the  muscles 
of  the  eyeball,  the  ear,  the  upper  third  of  the  esophagus,  diaphragm, 
and  tongue.  It  is  under  the  control  of  the  will,  hence  designated  volun- 
tary. The  striped  muscle  of  the  diaphragm  and  the  esophagus  is  appar- 
ently only  partially  voluntary. 

It  is  obvious  from  the  above  that  there  is  demanded  a  more  specific 
terminology:  involuntary  smooth  (unstriped) ;  involuntary  striped  (car- 
diac);  and  voluntary  striped  (skeletal).  The  three  types  pass  through 
very  similar,  perhaps  identical,  earlier  stages  of  histogenesis.  The  essen- 

90 


GENERAL  CONSIDERATIONS 


91 


tial  difference  seems  to  be  one  of  degree 
differentiation.  In  general,  skeletal  mus- 
cle is  most  highly  differentiated,  cardiac 
muscle  being  intermediate  between 
smooth  and  the  voluntary  striped  type. 

For  a  proper  understanding  of  the 
structure  of  these  three  types  it  is  neces- 
sary that  we  now  consider  the  process  of 
muscle  histogenesis.  The  student  should 
gather  the  several  criteria  by  which  he 
may  distinguish  between  smooth,  cardiac, 
and  skeletal  muscle,  both  in  transverse 
and  longitudinal  sections. 


HISTOGENESIS  AND  STRUCTURE 


Smooth  Muscle.— As  stated  above,  the 
germ  layer  involved  in  muscle  histogene- 
sis is  the  mesoderm.  Smooth  muscle  is 
derived  chiefly  (exception:  arrectores  pil- 
orum)  from  the  visceral  or  splanchnic 
layer.  This  is  at  first  an  epithelial  struc- 
ture of  a  single  layer  of  cells,  the  prim- 
itive mesothelium.  The  cells  subsequent- 
ly proliferate  and  change  their  shape  in 
general  to  a  fusiform  type.  Intercellular 
connections  (cytodesmata)  are  either 
maintained  or  established,  and  the  tissue 
is  permanently  more  or  less  in  a  syncytial 
condition.  These  so-called  intercellular 
bridges  are  particularly  pronounced  and 
can  be  readily  demonstrated  in  the  tunica 
media  of  the  blood-vessels  of  the  umbilical 
cord.  It  must  be  emphasized,  however, 
that  the  outlines  of  the  genetic  units  in 
smooth  muscle  are  always  distinct,  where- 
as in  striped,  especially  the  cardiac  type, 
the  outlines  of  the  original  myoblasts  are 
lost. 


FIG.    97. — SMOOTH  MUSCLE 
CELLS. 

A,  an  isolated  cell  from  the 
cat's  intestine.  The  nucleus  is 
surrounded  by  coarsely  granular 
sarcoplasm,  continuous  periph- 
erally with  the  finely  granular 
interfibrillar  sarcoplasm.  The 
innermost  myofibrils  may  er- 
roneously suggest  a  cell  mem- 
brane. The  fusiform  element  is 
invested  by  a  true  cell  mem- 
brane, or  sarcolemma.  X  750. 
B,  oblique  transverse  section  of 
a  cell  from  the  muscularis  mu- 
cosse  of  the  cat's  esophagus. 
The  perinuclear  sarcoplasm  has* 
contracted  away  from  the  nu- 
cleus leaving  a  clear  space  limited 
by  a  sharp  line,  external  to  which 
lies  the  perinuclear  granular  sar- 
coplasm. Hematoxylin  and 
eosin.  X  750. 


92  MUSCULAR  1  ISSUE 

The  early  myoblast,  of  short  spindle  shape  with  central  oval  nucleus, 
contains  a  granular  cytoplasm,  limited  hy  a  delicate  membrane,  the 
sarcolemma.  The  granules  may  be  called  myocliondria;  whether  identi- 
cal with  cytomicrosomes  or  with  mitochondria,  whether  of  cytoplasmic 


FIG.  98. — SMOOTH  MUSCLE  CELLS  FROM  THE  PIG'S  STOMACH. 
Isolated  in  equal  parts  of  alcohol,  glycerin,  and  water.     Unstained.     X  410. 

or  of  nuclear  origin,  are  disputed  points.  No  evidence  of  a  distinct 
spongioplasm  is  discernible.  This  observation  tends  to  invalidate  the 
teaching  of  certain  histologists,  that  the  contractile  fibrils  (myofibrils) 
represent  modified  spongioplasmic  threads  arranged  in  rectilinear  meshes. 


FIG.  99. — SMOOTH  MUSCLE  CELLS  PROM  THE  WALL  OF  THE  HUMAN  INTESTINE. 
Longitudinal  section.    Hematein  and  eosin.     X  665. 

Moreover,  it  has  been  established  by  direct  observation  (McGill,  et  al.) 
that  the  myofibrils  arise  through  process  of  alignment  and  subsequent 
fusion  of  the  myocliondria.  McGill  (Tnternat.  Monatschr.  Anat.  u.  Phys., 
Bd.  24,  1907)  recognizes  two  types  of  myofibrils,  namely,  stouter  periph- 
eral border  fibrils  (myoglia)  which  may  pass  beyond  the  limits  of  a 
cell  and  form  intercellular  bridges;  and  the  more  central,  or  myofibrils 


HISTOGENESIS  AND  STRUCTURE  93 

proper,  which  are  limited  to  the  cells  proper  and  are  considerably  more 
delicate.  It  is  believed  that  border  fibrils  may  subsequently  arise  by 
fusion  of  the  more  delicate  fibrils. 

The  function  of  the  border  fibrils  is  disputed,  some  claiming  that 
they  serve  to  straighten  the  cell  following  contrac- 
tion produced  by  the  central  fibrils,  others  claim- 
ing that  they  have  a  contractile  role  similar  to  the  • 
central  myofibrils.    Whatever  their  complete  func-    ':*  .  ^ 
tion  may  be,  they  certainly  seem  to  bind,  together            9 
with  the  connective  tissue,  the  individual  cells  into       •           »        ^ 
a  compact  tissue  in  which  coordinated  movement, 

as  in  peristalsis  of  the  intestine,  becomes  possi-   r 

FIG.    100.— SMOOTH 
ble — an  obviously  important  condition.  MUSCLE   CELLS 

The  oval  or  rod-shaped  nucleus  retains  its  cen-  FROM  THE  WALL  OF 
tral  location,  and  is  surrounded  by  a  mass  of  gran-  THE  HUMAN  INTES- 
ular,  relatively  undifferentiated  sarcoplasm,  con-  Transection  Hema- 
taining  mitochondria,  lipoid,  and  glycogen  gran-  tein  and  eosin.  X  750. 
ules.  It  changes  its  shape  with  the  phase  and 

degree  of  contraction,  occasionally  even  assuming  a  short,  spiral  form. 
It  has  been  shown  (McGill,  Amer.  Jour.  Anat.,  9,  4,  1909)  that  during 
contraction  the  nucleus  decreases  markedly  in  length  and  increases  in 
thickness ;  and  that  the  uniformly  distributed  chromatin  granules  stream 
toward  the  poles,  where  they  collect  in  coarse  strands.  This  structural 
intranuclear  change  is  apparently  unaccompanied  by  any  change  in 
volume. 

Smooth  muscle  cells  vary  greatly  in  size — from  the  shortest  of  about 
50  microns,  to  some  of  500  microns  in  length  in  the  pregnant  uterus. 
When  in  the  contracted  condition,  they  show  a  number  of  broad,  more 
deeply  staining  contraction  bands,  very  conspicuous  in  the  smooth  mus- 
cle of  the  lower  portion  of  the  esophagus.  As  seen  in  transverse  section 
these  fibers  vary  in  size  from  a  mere  point  up  to  their  maximum  diame- 
ter, according  as  the  section  happens  to  pass  through  the  end  or  through 
the  middle  of  a  fiber.  Because  of  its  central  location,  the  nucleus 
is  only  found  in  the  larger  transections. 

Smooth  muscle  fibers  may  be  joined  together  in  interlacing  groups 
as  in  the  wall  of  the  uterus  or  bladder;  or  they  may  form  broad  mem- 
branous layers  as  in  the  wall  of  the  alimentary  tract;  or  again, 
they  may  form  small  isolated  bundles,  as  in  the  skin.  In  any  case, 
the  muscle  bundles  are  united  by  a  delicate  network  of  connective 
tissue. 


94 


MUSCULAR  TISSUE 


Smooth  muscular  tissue  occurs  chiefly  in  the  walls  of  the  hollow  or 
tubular  viscera.    Its  distribution  may  be  classified  as  follows : 

(1)  In  the  alimentary  tract:  lower  portion  of  J;he  esophagus,  stom- 
ach, small  and  large  intestines. 

(2)  In  the  respiratory  system:  trachea  and  bronchial  tubes. 

(3)  In  the  genii o-urinary  system:  ureter,  bladder,  urethra,  penis, 
prostate,  vagina,  uterus,  oviduct,  and  ovary. 

(4)  In  the  vascular  system:  ar- 
teries, veins,  and  the  larger  lymphatic 
vessels. 

(5)  In  the  ducts  of  all  secreting 
glands:  gall  ducts  and  gall  bladder, 
and  the  ducts  of  the  pancreas,  sal- 
ivary glands,  testicle,  etc. 

(6)  It  is  also  found  in  the  cap- 
sules   of   the    spleen    and   lymphatic 
nodes,  in  the  skin,  and  in  the  intrin- 
sic muscles  of  the  eye. 

Small  numbers  of  branching  cells 
have  been  described  in  the  walls  of 
the  urinary  bladder  and  the  large 
arteries. 

Cardiac  Muscle. — Heart  muscle 
likewise  takes  origin  from  splanchnic 
mesothelium,  which  soon  becomes 
modified  into  a  loose-meshed  syncy- 
tium,  in  which  all  trace  of  the  orig- 
inal cellular  element  is  lost.  The 
myoblast  areas  of  stellate  and  irreg- 
ular form  contain  a  central  oval  nu- 
cleus and  a  finely  granular  cytoplasm. 
In  a  manner  similar  to  that  described 
for  smooth  muscle  histogenesis,  the 
myochondria  form  myofibrils  which 
extend  for  great  lengths  throughout 
the  sarcoplasmic  meshwork.  In  car- 
diac muscle  the  myofibrillae  subse- 
quently acquire  a  cross  striation.  Adult  muscle  consists  of  stouter  mus- 
cle fibers  or  trabeculae  joined  into  an  intricate  close  meshwork,  by  means 
of  less  robust  branches.  The  nuclei  retain  their  axial  position  in  the 


FIG.  101. — Two  STACKS  IN  THE  HIS- 
TOGENESIS   OF    SMOOTH    MUSCLE, 
FROM  THE  WALL  OF  THE  ESOPHAGUS 
OF  A  PIG  EMBRYO. 
A,  10   mm.  stage  of  development. 
The  central  nucleus  of  the  mesenchy- 
mal  syncytium  has  become  enlarged 
and  is  enveloped  by  a  greater  mass 
of  cytoplasm.     It  represents  a  myo- 
blast; the  peripheral  myochondria  have 
become  aligned  preparatory  to  fusion 
to  form  a  muscle  fibril.     B,  21  mm. 
stage  of  development.     Four  adjacent 
myoblasts,     with    peripheral  stouter 
myoglia  fibrils  and  central  more  deli- 
cate myofibrils.     X  1500. 


HISTOGENESIS  AND  STBUCTUEE 


95 


fibers  and  are  surrounded  by  an  oval  area  of  undifferentiated  granular 
sarcoplasm.  The  cardiac  fibers  and  their  branches  contain  peripheral 
myofibrils,  which  during  growth  of  the  muscle  arise  by  longitudinal 
splitting  of  the  original  fibrils  and  take  position  progressively  toward  the 
center.  Cardiac  muscle  thus  consists  of  a  slender  axial  core  of  undiffer- 
entiated sarcoplasm  swelling  to  an  oval,  more  expansive  mass  where  the 


Fi«.  102. — A  GROUP  OF  MYO- 

BLASTS    FROM    THE    HEART 

MUSCLE  SYNCYTIUM  OF  A 
48  HOUR.  CHICK  EMBRYO. 
Showing  myofibrils,  myo- 

chondria   and   mitochondria. 

The    latter    are    the    deeper 

staining    granules.      Meves' 

technic.     X  2000. 


FIG.  103. — CARDIAC 
MUSCLE  OF  GUINEA 
PIG,  SHOWING  SEV- 
ERAL BRANCHES, 
CROSS  STRIATIONS 
(GROUND  MEM- 
BRANES) AND  A  NUM- 
BER OF  INTERCALATED 
DISKS. 

Zimmermann's     tech- 
nic.    X  1000. 


nuclei  are  located ;  this  core  is  surrounded  by  successive  rows  of  myofibrils 
arranged  in  groups  representing  Cohnheim's  fields  in  transverse  section ; 
and  the  whole  is  invested  by  a  delicate  sarcolemma.  The  striations  of 
the  fiber  result  from  the  fact  of  a  transverse  alignment  of  identical  areas 
in  adjacent  fibrillae — a  correspondence  which  indicates  a  definite  func- 
tional stimulus  to  a  structural  modification  (Fig.  103).  The  sarcoplasm 
contains  mitochondria  (Fig.  102),  lipoid,  albuminoid  (interstitial  gran- 


96  MUSCULAR  TISSUE 

ules  of  Kolliker),  and  glycogen  granules.  Fat  granules,  'liposomes' 
(Bell)  of  probably  nutritive  significance,  and  varying  greatly  in  amount 
according  to  the  functional  condition  of  the  individual,  are  normally 
present  in  cardiac  muscle  (Bullard,  Amer.  Jour.  Anat.,  14,  1,  1912). 
This  fatty  content  can  be  demonstrated  by  the  several  microchemical 
technics  for  lipoids.  According  to  Meves,  Duesberg,  and  others,  the  myo- 
fibrils  of  striped  muscle  differentiate  from  the  mitochondria  of  the  myo- 
blasts;  but  since  mitochondria  can  be  demonstrated  in  highly  developed 


J 


FIG.    104. — CARDIAC   MUSCLE  'CELLS'  FROM    THE    PIG'S    HEART,    ISOLATED    IN 

EQUAL  PARTS  OF  ALCOHOL,  GLYCERIN,  AND  WATER. 
Unstained.     (The  nuclei  are  somewhat  darker  than  they  actually  appear.)      X  410. 

fibers  (Fig.  116)  it  seems  improbable  that  mitochondria  have  anything 
directly  to  do  with  the  development  of  muscle  fibrils. 

It  has  been  claimed  that  heart  muscle  and  striped  muscle  generally 
can  be  interpreted  in  terms  of  muscle  cells,  and  intercellular  myofi brills?, 
in  analog}7  with  connective  tissue  (Baldwin).  But  the  presence  of  a  con- 
tinuous axial  core  of  undifferentiated  sarcoplasm,  lack  of  a  definite  cell 
membrane  separating  this  sarcoplasm  from  the  outlying  myofibrillas,  in- 
ability to  separate  such  'cells'  by  dissociation  methods,  and  the  extension 
of  the  telophragma  to  the  nuclear  wall,  seem  to  render  this  view  unten- 
able. 

The  myofibrils  must  be  further  considered.  ISTo  distinction  between 
border  fibrils  and  central  fibrils,  as  in  smooth  muscle,  is  possible  in  car- 
diac muscle.  But  the  myofibrils  undergo  greater  differentiation.  This 


HISTOGENESIS  AND  STKUCTUKE  97 

expresses  itself  in  an  alternation  of  light  and  dark  disks  ('bands,'  'seg- 
ments/ 'stripes'),  said  to  consist  of  isotropic  and  anisotropic  substances 
respectively.  While  the  disks  are  conspicuous  both  in  fresh  and  stained 
tissue,  the  demonstration  of  their  physical  properties  under  the  polari- 
scope  is  a  matter  of  difficulty.  Indeed  with  crossed  Xichols  the  entire 


FIG.  105. — CARDIAC  MUSCLE  OF  THE  HUMAN  HEART;  THE  ABUNDANT  BRANCHES 

ARE  PLAINLY  SHOWN. 
Longitudinal  section.     Hematein  and  eosin.     Photo.     X   120. 

fiber  appears  lighter  than  the  field,  showing  the  presence  of  aiiisotropic 
^materials  (granules)  scattered  throughout  the  fiber,  but  a  definite  band- 
ing corresponding  to  the  light  and  dark  disks  of  fresh  muscle  is  not 
apparent  in  all  striped  muscle.  It  seems  more  probable  that,  though 
anisotropic  granules  are  more  abundant  in  the  dark  disk,  they  are  not 
absent  in  the  lighter  disk;  moreover,  they  are  more  or  less  definitely 
aggregated  in  the  dark  disk  according  to  the  phase  of  contraction.  The 


08 


MUSCULAE  TISSUE 


lighter  disk,  or  intermediate  disk  of  Krause,  is  commonly  designated  by 
the  letter  J  (Isotrope  streife)  ;  the  dark  disk,  or  transverse  disk  of 
Briicke,  by  the  letter  Q  (Querscheibe).  On  closer  inspection  the  J 

disk  is  seen  to  be  bisected  by  a 
dark  disk  or  membrane,  the 
ground  membrane  of  Krause. 
designated  by  the  letter  Z 
(Zwischenscheibe) .  Indeed 
this  is  the  most  conspicuous 
stripe,  and  gives  to  the  mus- 
uc  cle,  as  seen  under  ordinary 
low  magnification,  its  band- 
ed appearance  in  uncontracted 
fibers.  The  term  teloi>ln-it<nna 
has  recently  been  employed  by 


FIG.  106. — THE  CENTRAL  PORTION  OF  THE 
PRECEDING  FIGURE,  MORE  HIGHLY  MAG- 
NIFIED. 

o,  intercalated  disk;  en,  endothelial  nuclei 
of  a  capillary;  Nuc,  nucleus  of  muscle  syn- 
cytium.  '  Hematein  and  eosin.  X  500. 


Heidenhain  for  this  mem- 
brane. The  myofibrils  are  in- 
timately connected  with  it. 
Similarly,  the  Q  disk  is  bi- 
sected by  a  narrow  light  disk,  the  median  disk  of  Hensen  (H),  which  in 
turn  is  said  to  be  bisected  by  the  intermediate  membrane  of  Heidenhain, 
or  meeophragma  (M,  Mittelscheibe).  Both  telo-  and  mesophragmata 
(inophragmata)  are  supposed  to  unite  with  the  sarcolemma  peripherally, 
and  to  be  structurally  similar.  The  telophragma  is  in  intimate  connec- 
tion both  with  the  sarcolemma 

and  the  nuclear  membrane.  But  ^^  £ 

the   mesophragma,    at   least  in        (J-  W 

striped  muscle  of  certain  forms,  A 

e.g.,    Limulus,    is    not    a    true  A 

membrane  to  which  the  fibrils  • 

are  attached  in  the  manner  of 

the  telophragma.    Indeed  it  re-  4    %  1 

mains  an  open  question  whether  ^ 

heart  muscle  actually  possesses 
a  mesophragma. 

The  portions  of  a  fibril,  or 
sarcostyle,  included  between 
successive  telophragmata,  con- 
stitute structural  units,  the  sar- 
comeres,  or  inokommata  (Heidenhain,  Fig.  110).  In  macerating  fluids 


FIG.   107. — TRANSECTION  OF  A  GROUP  OF 
CARDIAC-  MUSTLE  FIBERS  FROM  A  PAPIL- 
LARY MUSCLE  OF  THE  HUMAN  HEART. 
Hematein  and  eosin.     X  550. 


• 
•     • 


HISTOGENESIS  AND  STRUCTURE  99 

fractures  occur  at  the  Z  lines.  These  membranes  extend  completely  across 
the  fiber,  through  the  axial  strand  of  sarcoplasm — a  significant  fact  con- 
troverting the  cellular  idea  of  cardiac  muscle  originally  advanced  by 
Apathy.  The  interstitial  granules  of  Kolliker  (sarcosomes  of  Retzius) 
scattered  throughout  the  Q  and  J  disks  in 
striped  muscle,  both  cardiac  and  skeletal,  A  m^ 

are  designated  the  Q  and  J  granules  re-  ^ 

spectively  (Holmgren). 

INTERCALATED  DISKS. — A  unique  char- 
acteristic of  cardiac  muscle  pertains  to  the 
presence  of  the  intercalated  disks,  func- 
tional lines/  or  bands  of  Eberth.  These 
arc  barely  visible  in  ordinary  .historic 
preparations,  but  can  be  rendered  conspic-  HUMAN  FETUS  AT  SEVEN 
uous  by  the  special  technics  of  Heidenhain  MONTHS. 
and  of  Zimmermann.  In  gross  appear-  Fibrillse  are  well  developed  at 
ance  they  are  of  several  sorts:  straight  ^/^^^^ 
bands,  step-like  forms,  and  serrated  forms,  presents  a  clear  appearance  and 
The  bands  (disks)  may  extend  completely  in  some  cases  *  partially  occu- 
across  a  fiber,  or  only  the  width  of  a  single  ^^^7^'  **""*** 
fibril  (granule  type) ;  the  step  form  may 

consist  of  one  or  many  groups  of  steps  and  risers,,  the  'risers'  being  the 
height  of  one  or,  occasionally,  several  inokommata;  the  saw-tooth  type 
also  may  be  of  small  or  greater  extent,  and  of  the  height  of  one  or  several 
inokommata.  All  three  types  may  be  arranged  in  rings  or  even  longer  or 
shorter  spirals.  The  intercalated  disks  are  peripheral  in  position,  extend- 
ing for  varying  depths,  but  never  completely  through  a  fiber,  and  never 
central  to  the  axial  sarcoplasm.  They  are  occasionally  on  the  same  level 
with  the  nucleus.  They  have  been  found  in  the  heart  qf  representatives 
of  all  the  animal  groups  to,  and  including,  teleost  fishes  (Jordan  and 
Steele).  They  are  present  sparsely  and  in  simple  form  also  in  the  heart 
of  Limulus.  They  are  probably  a  morphologic  incident  of  the  rhythmic 
contraction  of  cardiac  muscle.  They  appear  only  late  in  fetal  life,  toward 
the  end  of  the  last  week  of  gestation  in  the  guinea  pig. 

The  earliest  disks  are  all  of  the  coarsely  granular  band  type.  Subse- 
quently they  increase  in  number  and  complexity,  the  older  stages  being 
characterized  by  occasional  saw-tooth  forms.  Once  formed,  they  are 
evidently  for  the  most  part  permanent  structures,  undergoing  modifica- 
tion largely  through  mechanical  factors.  On  closer  inspection,  under 
the  higher  powers  of  the  microscope,  they  are  seen  to  consist  of  units 


100 


MUSCULAR  TISSUE 


FIG.  109. — CARDIAC  MUSCLE 

FIBERS. 

A,  portion  of  a  fiber  from  a 
macerated  preparation  of  a 
cat's  heart,  drawn  according 
to  its  appearance  in  the  opti- 
cal longitudinal  plane.  Two 
nuclei  are  shown,  connected 
by  a  continuous  axial  strand 
of  coarsely  granular  sarco- 
plasm.  The  sarcolemma  ap- 
pears festooned  between  suc- 
cessive ground  membranes. 
There  is  no  evidence  of  a  cell 
membrane  separating  the  cen- 
tral granular  from  the  periph- 
eral non-  or  finely-granular 
sarcoplasm.  X  1000.  B, 
median  longitudinal  section 
of  a  fiber  from  the  ventricle 
of  an  adult  white  mouse. 
Note  the  continuity  of  the 
axial  sarcoplasm.  Hematox- 
ylin  and  eosin.  X  1000. 


corresponding  to  portions  of  a  single  fibril. 
These  units  may  be  granular  or  compact. 
The  units  are  bisected  or  bounded  on  one  side 
by  the  Z  membrane.  Association  of  the  units 
in  transverse  lines  gives  rise  to  the  band 
forms;  they  may  be  drawn  into  spirals  by 
longitudinal  traction  of  the  fibers  involved; 
unequal-  transverse  and  oblique  tractions 
probably  produce  the  step  forms;  the  saw- 
tooth form  arises  by  process  of  longitudinal 
splitting  of  fibrils,  enlargement  of  fibers,  and 
the  various  tensions  characteristic  of  hyper- 
trophying  fibers.  The  exclusive  type  of 
hypertrophied  heart  muscle  is  the  more  or 
less  complex  saw-tooth  type.  The  practically 
exclusive  type  of  atrophied  heart  muscle  is 
the  'comb  type/  a  type  produced  from  a  band 
type  by  a  modification  involving  longitudinal 
tension  (Fig.  114,  d).  In  brief,  the  unit  of 
structure  is  a  modified  focus  on  a  myofibril, 
in  essence  involving  an  accumulation  of  gran- 
ules about  the  Z  membrane.  Such  foci  asso- 
ciated in  various  ways  produce  the  various 
types  of  bands  and  steps,  the  latter  in  part 
due  also  to  external  mechanical  factors,  the 
extreme  condition  of  such  effect  being  saw- 
tooth forms. 

A  significant  point  concerns  the  similarity 
between  the  phylogenetic  and  ontogenetic  de- 
velopment of  intercalated  disks :  that  is,  below 
birds,  as  in  all  fetal  hearts,  only  simple  bands 
appear;  in  birds  as  in  young  hearts,  step  forms 
are  present;  only  in  mammals  and  in  old 
hearts  do  the  more  complex  types  appear. 
What  then  is  the  meaning  of  these  disks  ?  Any 
interpretation  must  be  more  or  less  tentative 
at  present.  It  is  easier  to  say  what  they  prob- 
ably are  not,  than  what  they  probably  are. 
They  were  originally  interpreted  as  cell  boun- 
daries, or  intercellular  cement  lines  (Schweig- 


HISTOGENESIS  AND  STRUCTURE 


101 


ger-Seidel)  ;  this  interpretation  has  recently  been  again  supported  by 
Zimmermann.  This  interpretation  would  mean  that  from  a  syncytium  a 
cellular  tissue  has  secondarily  arisen  by  the  appearance  of  cement  lines, 
secondary  cells  having  been  formed  in  a  syncytium,  irrespective  of  the 
original  genetic  units.  A  number  of  facts  render  this  interpretation  inad- 
missible, chief  among  which  are  their  occasional 
supernuclear  position,  and  their  peripheral  loca- 
tion. A  more  recent  interpretation  conceives  of 
them  as  places  where  the  muscle  fiber  grows,  that 
is,  as  sarcomeres  in  the  making  (Heidenhain). 
Among  the  countervailing  facts  to  such  interpre- 
tation are  chiefly  the  absence  of  transition  stages, 
their  relative  scarcity  at  the  period  of  greatest 
growth  of  the  heart,  and  their  continued  abun- 

Telophr 


Q-granule 

Mesophragma 


Transverse 
—     fiber  net- 
work 


FIG.  111. — LONGI- 
TUDINAL SECTION 
OF  PORTION  OF 
WING  MUSCLE 
FIBER  OF  MANTIS, 
AT  MID-PHASE  OF 

CONTRACTION. 

z,  telophragma; 
h,  Hensen's  disk; 
j,  isotropic  disk; 
q,  anisotropic  disk; 
q.  s.,  g-sarcosome ; 
j.  s.,  j-sarcosome. 
X1600. 


FIG.      110.  —  DIAGRAM     OF    A 
STRIPED   MUSCLE  FIBER,  AC- 
CORDING TO  HEIDENHAIN. 
The  transverse  fiber  network 
may  be  a  trophospongium. 
dance  in  full-grown,  even  aged,  hearts.     The  suggestion  has  been  made 
that  they  are  related  to  a  phase  of  contraction.    This  seems  more  likely. 
Since,  once  formed,  disks  are  largely  permanent,  and  undergo  subsequent 
modification,  they  must  represent  an  irreversible  condition  of  the  con- 
traction phase.     The  interpretation  of  the  disks  as  irreversible  contrac- 
tion bands  rests  upon  the  similarity  of  the  simplest  types  and  the  con- 
traction bands  of  Rollet,  both  characterized  by  accumulation  of  dark  stain- 


102 


MUSCULAR  TISSUE 


ing  granules  about  the  Z  membrane.  In  the  older  hearts,  where  they  are 
mechanically  modified,  and  in  diseased  hearts,  as  in  hypertrophies,  where 
probably  a  chemical  modification  is  also  suffered,  they  represent  lines  of 
weakness.  These  are  the  locations  of  fracture  in  fragmented  and  segmented 
pathological  hearts — a  significant  point  in  relation  to  'heart  failure.' 

Heart  muscle  is  syncytial  in  structure,  and  the  myofibrillae  pass  unin- 
terruptedly through  the  intercalated  disks.  These  facts  are  of  special  im- 
portance because  of  their  bearing  on  the  opposed  theories  of  the  origin  and 
conduction  of  the  stimulus  to  the  heart  beat,  the  myogenic  and  the  neuro- 
genic.  A  complete  cellular  structure  with  actual  cement  lines,  combined 
with  the  fact  that  the  atria  are  apparently  completely 
separated  from  the  ventricles  by  intervening  con- 
nective tissue,  was  once  urged  as  a  strong  argument 
against  the  validity  of  the  myogenic  theory  of  heart 
beat — the  theory  which  proclaimed  the  adequacy  of 
heart  muscle  to  initiate  and  conduct  the  stimulus  to 
contraction  without  the  intervention  of  nerve  ele- 
ments, that  is,  to  beat  automatically  and  indepen- 
dently of  the  nervous  system.  The  neurogenic  the- 
ory, which  holds  that  nerve  elements  are  essential 
for  the  conduction  of  stimuli  for  contraction,  on  the 
other  hand,  seemed  contradicted  by  the  observation 
that  in  the  chick  the  heart  beat  rhythmically  before 
the  appearance  of  nerve  fibers.  However,  there  re- 
mained the  possibility  that  nerve  fibers  were  present 
but  undemonstrable  by  the  method  employed;  also 
that  while  nerves  might  be  unnecessary  for  maintain- 
ing rhythmic  contraction  during  embryonic  life,  they 
nevertheless  became  necessary  in  fetal  and  adult  life. 
The  discovery  of  the  atrioventricular  bundle  of 
His  (1893)  at  first  added  apparently  the  strongest 
evidence  to  the  support  of  the  application  of  the  myogenic  theory  of  heart 
beat  in  the  mammalian.  This  is  a  muscular  bundle  which  effects  an  inti- 
mate connection  between  the  atria  and  the  ventricles.  See  heart,  p.  199. 
An  important  matter  is  the  observation  that  the  final  ramifications 
of  the  bundle  of  His  are  identical  with  the  so-called  PurJcinje  fibers. 
These  have  long  been  known,  especially  in  the  sheep's  heart,  where 
they  are  unusually  large  and  abundant.  They  are  limited  to  a  region 
directly  under  the  ventricular  endocardium.  They  are  coarser,  less 
branched,  with  fewer  intercalated  disks,  almost  exclusively  of  the  band 
type,  than  are  the  fibers  of  the  myocardium  proper.  They  would 


FIG.  112. — LONGI- 
TUDINAL SECTION 
OF  PORTION  OF 
ATRIO  -  VENTRICU- 
LAR BUNDLE  OF 
HEART  OF  BEEF. 
MANY  OF  THE 
CELLS  ARE  BINU- 

CLEATED.     X  160. 


HISTOGENESIS  AND  STRUCTURE 


103 


seem  to  represent  a  younger  or  less  highly  differentiated  stage  of  muscle 
fiber.    In  cross  section  they  are  of  greater  diameter,  with  fewer  peripheral 
myofibrils  and  a  far  greater  amount  of  central  undifferentiated  sarco- 
plasm,  rich  in  glycogen.    According  to  Lange  (Arch.  mikr.  Anat.,  Bd. 
84,  1914)  the  Purkinje  fibers  cannot,  however,  be  regarded  as  remains  of 
embryonic  muscle  cells,  since  they  are  clearly  distinguishable  already  in 
very  young  mammalian  embryos ;  they  constitute  the 
non-nervous  apparatus  for  conducting  stimuli  to  heart 
beat. 

The  myogenic  theory  accordingly  seemed  well  es- 
tablished.   It  was  apparently  strongly  supported  by  the 

experiments    of    Erlanger    (1906),    who    clamped    the 

bundle  in  the  dog's  heart  and  produced  a  condition  of 

'heart  block' — a  disturbance  of  the  coordinated  rhyth- 

micity  of  the  atria  and  ventricles — without,  however, 

interfering  with  the  conduction  of  impulse,  since  there 

resulted  no  stoppage  of  contraction  in  the  ventricles. 

But  the  subsequent  discovery  of  abundant  nerve  fibers 

and  ganglion  cells  (Tawara,  Wilson,  McGill)   in  the 

bundle,  intimately  related  to  the  cardiac  fibers,  robbed 

this  experiment  of  its  specific  applicability  and  seemed 

for  a  time  to  force  an  interpretation  favoring  the  neu- 

rogenic  theory.     Carlson,  moreover,  demonstrated   its 

validity    for     the     Limulus     heart,    which,    after     the 

removal  of  its  ganglion,   could  not  be  made  to  beat. 

But  more  recently  Burrows    (1911)    has  shown  that 

single  cells  of  a  14-  to   18-day  embryo  chick  heart, 

grown  in  artificial  culture  media,  may  begin  to  beat 

automatically  and  rhythmically — an  observation  which 

would  seem  to  settle  the  point  that  heart  muscle  may 

beat  rhythmically  in  the  absence  of  nerve  supply  or 

even  nerve  stimulus. 

Furthermore,  Hooker  (Jour.  Exp.  Zool.,  11,  2,  1911)  showed  that  in  the 
frog  larvae  in  which  the  nervous  system  was  entirely  removed,  the  cardiac 
muscle  will  differentiate  and  function  normally,  independently  of  nervous 
control.  The  myogenic  theory  is  further  supported  by  the  fact  that  it  has 
been  possible  to  revive  the  excised  heart  of  man  to  rhythmic  activity  20 
hours  after  death  (Flack,  "Further  Advance  in  Physiology,"  Ed.,  Hill,  1909), 
whereas  the  longest  time  that  a  nerve  cell  is  known  to  survive  (in  the  intes- 
tine) is  3V2  hours  (Cannon  and  Eurkeit,  Amer.  Jour.  Phys.,  vol.  32,  p.  347, 
1913).  In  the  superior  cervical  ganglia,  nerve  cells  may  survive  1  hour, 
while  in  the  brain  the  maximum  time  of  survival  is  said  to  be  15  minutes. 


FIG.  113. — LONGI- 
TUDINAL SECTION 
OF  A  TRABECULA 
OP  LIMULUS 
(KING  CRAB) 
HEART  MUSCLE, 
SHOWING  AN  IN- 
TERC ALATED 
DISK  SEPARAT- 
ING A  CONTRACT- 
ED FROM  AN  UN- 
CONTRACTED 
PORTION. 

Nitric  acid-alco- 
hol fixation  (Zlm- 
mermann's  tech- 
nic),  iron-hematox- 
ylin  stain.  X  1300. 


104 


MUSCULAR  TISSUE 


Any  interpretation  of  the  intercalated  disks  as  actual  intercellular  struc- 
tures (cement  substance)  would  seem  inconsistent  with  the  myogenic  theory 
of  the  heart  beat,  which  now  seems  largely  to  prevail.  The  present  status 
of  the  matter  seems  to  be  that  the  origin  of  stimulus  to  heart  beat  in 
vertebrates  is  myogenic,  in  invertebrates  probably  neurogenic.  The  differ- 
ence may  inhere  in  the  absence  in  the  hearts  of  invertebrates  of  a  muscular 
coordinating  structure  analogous  to  the  atrioventricular  bundle  of  verte- 
brate hearts. 


FIG.  114. — SEMIDIAGRAMMATIC  ILLUSTRATIONS  OF  VARIOUS  TYPES  OF  INTERCALATED 

DISKS. 

a,  from  guinea  pig's  heart;  b,  from  chipmunk's  heart;  c,  from  monkey's  heart; 
d,  from  monkey's  heart;  e,  from  guinea  pig's  heart;/,  from  chipmunk's  heart.   X  1200. 

Voluntary  Striped  or  Skeletal  Muscle. — The  unit  of  structure  of 
skeletal  muscle  is  essentially  the  same  as  that  described  for  cardiac  mus- 
cle, namely,  a  myofibril  or  sarcostyle.  The  fiber  is  likewise  divisible  into 
successive  sarcomeres  or  iiiokommata.  A  difference  in  detail  inheres  in 
a  greater  definiteness  of  striation,  and  a  greater  complexity,  due  to  the 
presence  generally  of  an  additional  disk  in  the  J  stripe.  This  stripe 
or  accessory  disli  of  Engelmann  (X  line;  nebenscheibe)  bisects  the 


HISTOGENESIS  AND  STRUCTURE 


105 


portion  of  the  J  disk  between  the  Z  line  and  the  succeeding  Q  disk. 
It  is  interpreted  more  or  less  tentatively  by  Heidenhain  as  due  to  a  linear 
arrangement  of  J  granules.  The  median  segment  of  the  J  disk,  that  is, 

the  portion  between  the  N  line  and 
the  Z  line,  is  called  the  terminal 
disk  of  Merkel  (E  disk;  endscheibe). 
This  complex  condition  of  striping  is 
conspicuous  only  in  certain  insect 
muscles  (e.g.,  leg  and  wing  muscles 
of  wasp,  etc.)  where  powerful  activity 
or  great  rapidity  of  beat  is  required. 
In  general,  complexity  of  striation  of 
conspicuous  character  corresponds 
with  a  relatively  greater  irritability 
and  a  capacity  for  more  powerful  or 
relatively  more  rapid  function. 

Another  difference  between  skel- 
etal and  cardiac  muscle  pertains  to 
the  diameter  of  the  fiber  and  the  posi- 
tion of  the  nucleus.  In  skeletal  mus- 


FIG.  115. — SUCCESSIVE  STAGES  OP 
SKELETAL  MUSCLE  HISTOGENESIS 
IN  MAMMALS. 

a,  myoblast  with  fine  cytoplasmic 
granules  (myochondria),  from  a  13 
mm.  sheep  embryo;  b,  myoblast 
with  homogeneous  myofibrils,  from 
a  10  mm.  guinea-pig  embryo;  c, 
myoblast  with  cross  striped  fibrils, 
from  a  8.5  mm.  rabbit  embryo. 
(From  Heidenhain,  after  Godlew- 
ski.) 


FIG.  116. — TRANSVERSE 
SECTION  OF  A  STRIPED 
MUSCLE  FIBER  OF  A 
NEWLY-HATCHED  RAIN- 
BOW TROUT,  SHOWING 
THE  PROCESS  OF  MYO- 
FIBRIL  INCREASE  BY  RA- 
DIAL LONGITUDINAL 
SPLITTING. 

Mitochondria  are  seen  in 
the  peripheral  sarcoplasm 
and  around  the  nucleus  at 
the  right.  Meves'  technic. 
X  2000. 


cle  the  fiber  has  a  greater  diameter,  is  more  nearly  circular  in  cross  sec- 
tion, the  myofibrils  are  scattered  throughout  its  diameter,  and  the  nuclei 
are  peripheral,  lying  just  beneath  the  sarcolemma.  The  nuclei  are  envel- 


106 


MUSCULAR  TISSUE 


FIG.  117. — STRIATED 
MUSCLE  FIBERS  RUP- 
TURED BY  TEASING, 
SHOWING  THE  SARCO- 

LEMMA. 

a,  ruptured  end  of  the 
muscle  fiber;  B,  a  bundle 
of  fibrils  projecting  from 
the  torn  end;  m,  a  muscle 
fiber;  n',  a  nucleus  of  the 
muscle  cell;  at  p,  the 
muscle  substance  has 
shrunken  away  from  the 
sarcolemma;  s,  sarcolem- 
ma.  Moderately  magni- 
fied. (After  Ranvier.) 


oped  in  a  small  amount  of  granular  sarcoplasm. 
The  sarcolemma  is  a  homogeneous,  plastic,  non- 
nucleated  membrane,  the  representative  and 
product  of  the  cell  membrane  of  the  original 
myoblasts. 

In  routine  laboratory  preparations  only  the 
Z,  Q,  and  J  stripes  are  conspicuous.  Meigs 
(Zeitschr.  allg.  Phys.,  8,  1,  1908)  recognizes  at 
most  only  three  different  substances  in  striped 
muscle  sarcostyles  (fresh  wing  muscle  of  fly)  : 
Q,  Z,  and  M.  He  regards  J  and  H  as  optical 
effects  dependent  upon  the  reflection  of  light  by 
the  Z  and  M  membranes. 

Thulin  (Arch.  mikr.  Anat,  86,  3,  1915) 
records  the  absence  of  both  Z  and  M  membranes 
in  the  wing  muscles  of  certain  insects  (Coleop- 
tera)  and  the  analogous  (pectoral)  muscles  of 
birds  and  bats. 

'  The  perinuclear  sarcoplasm  contains  filar  and 
granular  mitochondria.  Both  the  perinuclear 
and  interfibrillar  sarcoplasm  contain  also  fat 
granules  and  globules  (liposomes),  interstitial 
granules  of  Kolliker  and  glycogeu. 

Heidenhain  (Anat.  Anz.,  44,  11-12,  1913)  has 
conclusively  shown  that  in  the  trout  embryo  the 
progenitor  (the  manner  of  whose  origin  is  un- 
known) of  the  definitive  myofibrillae  is  a  single, 
stout,  deeply  staining  column,  close  to  the  nuclear 
wall  externally,  which  undergoes  a  succession  of 
radial  and  concentric  longitudinal  divisions.  This 
observation  would  seem  to  dispose  of  the  assump- 
tion of  a  direct  mitochondrial  origin  of  myofibril- 
lae in  this  form  at  least,  in  the  manner  of  the 
current  descriptions.  And  this  conclusion  is 
strengthened  by  the  demonstration  of  mitochon- 
dria throughout  the  earlier  development  (Fig. 
116). 

Skeletal  muscles  develop  from  a  portion  of 
the  mesodermic  segments  qr  primitive  somites, 
called  the  myotomes.  The  myoblasts  pass  through 


FIG.  118. — ISOLATED  FRAGMENTS  OF  STRIATED  MUSCLE  FIBERS,  UNSTAINED. 

The  one  above  is  from  the  end  of  a  fiber;  that  on  the  right  shows  at  one  end  a 
tendency  to  cleavage  into  transverse  disks.     X  360. 


FIG.  119. — STRIATED  MUSCLE  FIBERS  OF  THE  DOG,  SEEN  IN  TRANSECTION. 
The  areas  of  Cohnheim  are  indistinctly  outlined.    Hematein  and  eosin.     X  490. 

107 


108 


MUSCULAR  TISSUE 


the  early  histogenetic  changes  already  described  for  cardiac  muscle.  In 
the  frog,  irritability  was  shown  by  Hooker  to  follow  closely  upon  differen- 
tiation of  the  fibrillae,  and  the  establishment  of  nervous  connections. 
The  adult  skeletal  muscle  fiber  is  a  multinucleated  structure.  Is  this 
condition  the  result  of  fusion  of  distinct  myoblasts,  or  of  growth  of  a 
single  myoblast  accompanied  by  nuclear  proliferation  ?  Both  interpreta- 
tions have  been  advanced ;  manv  observational  data  tend  to  show  that 


FIG.  120. — A  PORTION 
OF  A  STRIATED  MUS- 
CLE FIBER  SEEN  IN 
LONGITUDINAL  SEC- 
TION. 

The  alternate  light' 
and  dark  cross  stria- 
tions  are  well  shown. 
h,  light  line,  Hensen's 
line,  in  the  middle  of 
the  dark  disk  Q.  z, 
dark  line,  Krause's 
membrane  or  Dobie's 
line,  in  the  middle  of 
the  light  disk.  Hema- 
tein.  X  1200.  (After 
Bohm  and  von  David- 
off.) 


FIG.  121.— A  SMALL 
PORTION  OF  A  MUS- 
CLE FIBER  OF  A 
CRAB  SHOWING  BE- 
GINNING SEPARATION 
INTO  FIBRILS. 

Drawn  from  a  pho- 
tograph. X  600.  (After 
Schafer.) 


a  skeletal  muscle  fiber  represents  a  myoblast  which  has  elongated  and 
multiplied  its  nuclei.  In  the  trout  embryo,  however,  considerable  fusion 
of  myoblasts  occurs.  The  mode  of  nuclear  division  appears  to  be  at  first 
mitotic,  and  subsequently  amitotic.  In  the  tongue  a  small  number  of 
branched  fibers  have  been  described. 

Striped  muscle  fibers  differ  in  the  relative  amounts  of  myofibrillar  and 
sarcoplasmic  content.  When  the  myofibrillae  are  relatively  preponder- 
ant and  the  interstitial  granules  sparse,  the  fiber  is  known  as  'light'; 


HISTOGENESIS  AND  STRUCTURE 


109 


when  the  sareoplasm,  with  its  interstitial  granules,  is  relatively  abundant. 
:dark/    In  the  latter  fibers  many  of  the  nuclei  may  be  centrally  located. 


.  I 

«     y 

a  : 

»    5 
&     I 

3  I 


« 


Fro.   122. — FIBRILS  FROM  THE  WING 
MUSCLES  OF  A  WASP. 

A,  compressed;  B,  stretched;  C,  un- 
contracted.  The  alternate  dark  and 
light  disks  are  prominent;  the  mem- 
brane of  Krause  in  the  light  disk,  and 
the  line  of  Hensen  in  the  dark  disk  are 
well  shown.  Very  highly  magnified. 
(After  Schiifer.) 


FIG.  123. — LONGI- 
TUDINAL SECTION 
OF  A  PORTION  OF 
A  STRIPED  MUS- 
CLE TRABECULA 

OF     LlMTJLUS, 

SHOWING  A  NU- 
CLEUS OF  SER- 
RATED CONTOUR 
WITH  THE  TELO- 

PHRAGMATA  AT- 
TACHED TO  THE 
SERRATIONS. 

The  nucleus  lies 
in  an  undifferenti- 
ated  mass  of  sarco- 
plasm  containing 
below  a  deutoplas- 
mic  granule.  The 
adjacent  myofibrils 
simulate  a  cell  mem- 
brane. Fleming's 
fluid,  iron-hematox- 
ylin.  X  2000. 


Most  mammalian  muscles  contain  both  types  of  fibers,  but  with  the 
'light'  greatly  in  excess.  When  a  muscle  consists  chiefly  of  'light'  fibers 
it  is  a  'white'  muscle;  when  the  'dark'  fibers  are  abundant  it  may  be 


110 


MUSCULAE  TISSUE 


called  'red'  muscle.  The  former  variety,  for  example  the  biceps  muscle, 
acts  more  energetically  but  is  more  easily  fatigued;  the  latter,  like  the 
muscles  of  mastication,  respiration,  the  eyeball,  and 
cardiac  muscle,  are  functionally  characterized  by 
slower  activity  but  less  ready  fatigue.  The  intersti- 
tial granules  accordingly  seem  to  be  of  nutritive  sig- 
nificance. They  are  generally  more  abundant  in  the 
J  than  in  the  Q  segments.  The  J  granules  are  of 
spherical  form  and  smaller  than  the  oval  Q  granules. 
Striped  muscle  fibers  contain  also  a  trophospongium 
(Holmgren).  Adult  muscle  cannot  regenerate,  but  is 
replaced  by  scar  tissue.  A  young  fiber  is  said  to  be 
able  to  regenerate,  the  process  involving  movement  of 
proliferating  nuclei  toward  the  cut  surface.  Muscle 
growth,  as  with  exercise,  depends  upon  enlargement 


FIG.  124. — S  T  R  i  A  T  E  D 
FIBER  FROM  A  LEG 
MUSCLE  OF  THE  SEA 
SPIDER  (A  N  o  p  L  o  - 

DACTYLUS     LENTUS), 

SHOWING  THE  COM- 
PLEXLY STRIPED  CON- 
DITION CHARACTER- 
ISTIC OF  INSECT  MUS- 
CLE. 

Q,  anisotropic  disk;  J, 
isotropic  disk;  M(  mem- 
brane of  Heidenhain 
(mesophragma) ;  Z, 
membrane  of  Krause  (telo- 
phragma);  H,  median  disk 
of  Hensen;  N,  accessory 
disk  of  Engelmann;  E, 
terminal  disk  of  Merkel. 
X  1000. 


FIG.  125. — SEMIDIAGRAMMATIC  DRAWING,  REP- 
RESENTING THE  APPEARANCE  OF  THE  SAME 
FIBER  FROM  THE  LEG  MUSCLE  OF  A  BEETLE  IN 
ORDINARY  AND  POLARIZED  LIGHT. 

A,  appearance  in  ordinary  light;  B,  appearance 
•  in  polarized  light.     (After  Meigs.) 


of  the  muscle  fiber,  consequent  upon  a  multiplication  of  fibrillse  by  process 
of  longitudinal  splitting,  and  their  individual  enlargement. 


MUSCULAB  CONTRACTION 


111 


MUSCULAR    CONTRACTION 


Sarcolemma 


The  physics  and  chemistry  of  muscle  constituents  are  too  inadequately 
known  to  permit  anything  like  a  confident  description  of  the  mechanism 
of  contraction.  It  has  been  suggested  that  muscular  contraction  is  essen- 
tially a  reversible  coagulation  process.  The  rapidity  of  the  process  seems 
a  fatal  objection  to  this 
explanation.  A  plaus- 
ible interpretation  fol- 
lows the  analogy  afford- 
ed by  the  action  of  cat- 
gut suspended  in  water, 
the  temperature  of  which 
is  suddenly  raised  by 
passage  of  an  electric 
current,  namely,  a  swell- 
ing and  consequent 
shortening  of  the  fiber 
(Engelmann).  In  mus- 
cle, the  myofibrillaB  may 
be  conceived  of  as  cor- 
responding to  the  catgut 
of  the  experiment,  the 
semifluid  sarcoplasm  to 
the  water,  and  the  nerve 
impulse  to  the  electric 
current.  The  rapidity 
of  muscular  activity, 
however,  again  seems  a 
difficulty.  However,  the 
optical  changes  under- 
gone by  a  contracting 
muscle  give  evidence  in 


FIG.  126. — LATERAL  CONTRACTIVE  WAVE  OF  CASSIDA 
EQUESTRIS.     (After  Rollet.) 

The  formation  of  the  contraction  band  is  well  seen, 
at  the  left,  as  thick  black  lines.  (From  Szymonowicz- 
MacCallum,"  Histology  and  Microscopic  Anatomy.") 


favor  of  such  interpreta- 
tion. The  fibrillse  short- 
en and  thicken  in  con- 
traction, and  there  is  a 
rearrangement  of  the  optically  different  substances  of  the  fiber;  the  dark 
granules  aggregate  about  the  Z  line,  so  that  it  seems  to  have  disappeared — 
a  change  which  involves  also  the  disappearance  of  the  original  Q  stripe. 
We  may  be  fairly  certain  that  the  explanation  of  muscular  contraction  must 
be  sought  for  in  physical  and  chemical  changes  in  the  myofibril,  it  being 


112 


MUSCULAB  TISSUE 


the  essential  contractile  element,  the  sarcoplasm  serving  largely  as  a  nutri- 
tive substance.  However,  it  should  also  be  mentioned  that  it  has  been  held 
that  the  sarcoplasm  may  be  the  essential  contractile  substance. 

Meigs  questions  the  pertinency  of  Engelmann's  'artificial  muscle'  in 
his  catgut  experiment,  and  the  validity  of  the  suggested  hypothesis  of  con- 
traction as  a  thermodyiiamic  phenomenon.  He  regards  contraction  as 
the  result  of  a  rise  in  osmotic  pressure  and  the  consequent  imbibition 
of  fluid  caused  by  the  breaking  down  of  larger  into  smaller  molecules 
within  the  sarcostyles.  According  to  Roaf  (Proc.  Roy.  Soc.,  Series  B.  88, 
1914)  contraction  can  be  explained  on  the  hypothesis  that  lactic  acid  is 
set  free,  and  that  this  combines  with  certain  proteins  to  form  salts,  with 
a  consequent  rise  of  osmotic  pressure. 

We  must  now  consider  the  muscle  as  a  whole.  For  this  purpose 
we  may  select  any  well-known  muscle,  for  example,  the  biceps.  A  muscle 

as  seen  in  transverse  section 
is  enveloped  in  a  moderately 
dense,  fibro-elastic  mem- 
brane, the  epimysium  (ex- 
ternal perimysium) ;  this 
gives  off  septa  which  sep- 
arate the  muscle  into  a 
larger  or  smaller  number  of 
bundles,  depending  upon  its 
size,  each  bundle,  or  fascicu- 
lus, being  again  separately 
closely  enveloped  in  a  fibro- 
elastic  covering,  the  peri- 


FIG.   127. — STRIATED  MUSCLE  FIBERS 
DOG. 


The  blood-vessels  have  been  filled  by  injection 
with  a  gelatinous  mass  and  are  represented  in 
black.  One  whole  fasciculus  and  one  fiber  from 
an  adjacent  fasciculus  have  been  included,  a, 
perimysium;  b,  endomysium;  c,  a  large  vein  seen 
in  transection.  The  section  was  not  stained. 
X  53. 


mysium  (internal  perimy- 
sium). Each  fasciculus  is, 
moreover,  again  subdivided 

into  larger  and  smaller  collections  of  muscle  fibers,  each  bundle  imper- 
fectly separated  from  its  fellows  by  septa  from  the  perimysium,  the  endo- 
mysium. The  ultimate  subdivisions  of  the  endomysium  completely  en- 
velop each  fiber  and  blend  with  the  sarcolemma.  This  brings  us  to  an 
individual  fiber.  Each  fiber  is  enclosed  in  a  sarcolemma.  The  myofibrillae 
are  collected  into  larger  and  smaller  bundles,  Ko'Uiker's  columns,  sepa- 
rated from  each  other  by  semifluid,  granular  sarcoplasm;  these  collec- 
tions in  cross  section  are  known  as  the  areas  of  Cohnheim.  They  repre- 
sent the  definitive  division  products  of  the  original  group  of  fibrils  (Heid- 
euhain).  The  ultimate  histologic  units  are  the  myofibrilla  or  sarcostyles. 


MUSCULAR  CONTRACTION  113 

But  these  may  consist  of  still  more  delicate  fibrils;  in  Limulus  muscle, 
for  example,  the  myofibrils  may  be  resolved  into  successively  finer  fibrils 
to  the  limits  of  visibility. 

Heart  muscle  can  be  similarly,  but  less  precisely  divided,  the  endo- 
cardium and  epicardium  corresponding  to  the.  epimysium.  Fasciculi  and 
perimysium  are  not  so  readily  distinguished,  but  the  endomysium  is  re- 


FIG.  128. — STRIATED  MUSCLE  OF  A  CAT  SEEN  IN  TRANSECTION. 

The  blood-vessels  have  been  injected  and  are  black  in  the  figure.  At  a  an  artery  is 
contracted  and  empty.  The  heavy  black  vessels  are  veins  and  arterioles;  the  small 
black  dots  are  capillaries  in  transection.  One  whole  fasciculus  is  represented  and  is 
surrounded  by  a  delicate  perimysium  of  connective  tissue.  Between  the  muscle 
fibers  is  the  still  more  delicate  endomysium.  The  larger  vessels  are  almost  exclusively 
found  in  the  perimysium.  The  section  was  not  stained.  X  80. 


lated  to  cardiac  muscle  in  a  manner  essentially  similar  to  that  described 
for  skeletal  muscle. 

The  student  should  have  well  in  hand  the  several  criteria  for  the 
differentiation  of  the  three  types  of  muscle,  both  in  transverse  and 
longitudinal  sections;  and  of  smooth  muscle  from  the  dense  white 
fibrous  connective  tissue.  In  brief,  cross  sections  of  skeletal  striped  muscle 
can  be  readily  distinguished  on  the  basis  of  their  greater  diameter  and 
the  peripheral  position  of  the  nucleus.  Both  cardiac  and  smooth  muscle 


114  MUSCULAK  TISSUE 

have  a  central  nucleus  and  peripheral  fibrillae;  but  the  fibers  of  the 
cardiac  muscle  are  more  or  less  polygonal  in  outline  and  more  constant 
in  size,  excepting  occasional  branches,  while  the  smooth  cells  are  circular 
in  outline  and  of  very  diverse  diameters,  depending  upon  the  different 
levels  at  which  the  section  passes  through  adjacent  fusiform  cells.  In 
longitudinal  sections  the  cardiac  muscle  can  be  easily  recognized  by  its 
branching  character  and  the  presence  of  intercalated  disks ;  smooth  mus- 
cle by  the  fusiform  character  of  its  associated  cells.  Smooth  muscle  is 
frequently  difficult  to  distinguish  from  compact,  white  fibrous  connective 
tissue.  When  both  are  present  in  the  same  section,  stained  with  the 
routine  hematbxylin-eosin  technic,  the  two  exhibit  a  slight  difference  in 
staining  reaction.  The  smooth  muscle  commonly  stains  a  deeper  red; 
the  collagenous  fibers  have  a  lighter  orange  tinge.  Moreover,  from  a 
morphological  standpoint,  while  portions  of  the  white  fibrous  connective 
tissue  may  appear  spindle-shaped,  thus  simulating  the  unit  of  smooth 
muscle  structure,  the  associated  nuclei  of  enveloping  connective  tissue 
cells  are  peripheral  to  the  bundle,  whereas  the  nucleus  of  smooth  muscle 
is  of  course  in  the  center  of  the  analogous  structure,  the  muscle  cell. 


BLOOD    SUPPLY 

The  blood-vessels  of  voluntary  striped  muscle  distribute  their  larger 
trunks  within  the  connective  tissue  of  the  epimysium.  The  smaller 
branches  penetrate  the  endomysium  and  supply  a  rich  capillary  plexus 
with  long  rectangular  meshes.  This  network  of  capillaries  surrounds 
the  muscle  fibers  so  completely  that  each  fiber  is  placed  in  relation  with 
folir  or  five  capillary  vessels  which  run  parallel  with  the  long  axis  of  the 
fiber.  The  blood  supply  of  cardiac  muscles  is  in  general  similar,  but 
even  more  abundant  and  intimate,  with  respect  to  its  terminal  meshes. 
The  blood  supply  of  smooth  muscle  is  relatively  meager. 

Numerous  lymphatics  occur  in  the  peri  vascular  connective  tissue. 
These  lymphatic  vessels  are  especially  abundant  in  cardiac  muscle. 


NERVE    SUPPLY 

Skeletal  muscle  is  innervated  both  by  cerebrospinal  and  sympathetic 
nerves,  supported  in  the  connective  tissue  envelopes  and  septa.  The 
former  include  both  sensory  and  motor  fibers  ending  in  muscle  spindles 


TENDONS 


115 


and  motor  end-organs  respectively.  These  endings  will  be  further  de- 
scribed under  Peripheral  Nerve  Terminations.  The  sympathetic  or  'ac- 
cessory fibers'  (Fig.  129) — relatively  sparse  and  delicate,  and  in  close 
relationship  to  the  motor  fibers  and  endings — terminate  in  special  'end- 
plates/  close-meshed  networks  of  generally  oval  outline.  Boeke  (Anat. 
Anz.,41,  15-16,  1913)  sug- 
gests that  they  may  me- 
diate the  maintenance  of 
muscle  tone. 

Cardiac  muscle  is  sup- 
plied only  with  sympa- 
thetic motor  fibers.  These 
terminate  on  the  muscle 
fibers  in  brushes  of  fibrils, 
but  without  highly  spe- 
cialized endings.  Sensory 


FIG.  129. — MOTOR  END-PLATE  ON  AN  INTERCOSTAL 
MUSCLE  FIBER  OF  A  YOUNG  RABBIT. 

The  motor  nerve  fiber  ra  is  accompanied  by  an 
accessory  (sympathetic)  fiber,  a/.  (After  Boeke, 
Anat.  Anz.,  44,  15,  1913.) 


fibrils  from  the  vagus  are 

distributed  to  the  cardiac 

endomysium.  Each  smooth 

muscle  cell,  likewise,  is  supplied  with  a  sympathetic  fibril,  ending  in 

minute  knobs  or  plates. 

According  to  Malone  (Amer.  Jour.  Anat.,  15, 1, 1913),  the  three  types 
of  muscle  are  innervated  by  three  histologically  distinc£  types  of  nerve 
cells,  representing  specific  functional  differences.  The  cells  supplying 
heart  muscle  are  from  the  standpoint  of  size  and  granular  (chromophilic) 
content,  intermediate  between  those  supplying  smooth  and  those  supply- 
ing skeletal  striped  muscle.  (See  Fig.  139  below.) 


TENDONS 

A  tendon,  taken  as  a  whole,  is  invested  by  a  dense  fibro-elastic 
membrane,  the  epitendineum,  or  vagina  fibrosa.  Where  tendons  play 
in  bony  grooves  this  may  be  modified  into  a  tendon  sheath,  the 
epitendineum  acquiring  a  mucous  cavity,  when  it  becomes  known  as  a 
vagina  mucosa.  Septa  from  the  epitendineum  penetrate  the  mass  and 
divide  the  tendon  imperfectly  into  irregular  columns,  the  tertiary 
bundles.  These  are  further  divisible  into  more  regular  aggregations 
of  fibrils,  completely  enveloped  by  a  peritendineum,  and  are  the  ten- 
don fasciculi.  These  correspond  to  the  muscle  fasciculi  enveloped  by 


116 


MUSCULAE  TISSUE 


FIG.    130. — PORTION   OF   A   TRANSECTION   OF   A   LARGE 

TENDON. 

a,  fibrous  capsule  with  circular,  and  at  b,  longitudinal 
bundles  of  connective  tissue;  c,  d,  and  c,  fibrous  septa  be- 
tween the  fasciculi  of  the  tendon;  I,  lymphatic  cleft. 
Moderately  magnified.  (After  Schafer.) 


perimysium.  In  the 
mouse,  tendons  con- 
sist of  from  1  to  11 
fasciculi ;  in  the 
chick  from  2  to  5 
(Loevy,  Anat.  Anz., 
45,  10-11,  1913). 
Each  fasciculus  con- 
sists of  elementary 
bundles  of  collage- 
nous  fibrils,  envel- 
oped by  a  complete 
sheath  formed  by 
the  anastomosing 
processes  of  the  ten- 
don cells  (cells  of 
Kanvier).  The  cell 
bodies  lie  between 
these  primary  bun- 
dles; they  are  connected  to  each  other  by  their  processes,  forming  an 
'endotheliaF  tube  (Ranvier),  the  cells  of  which  have  a  characteristic 
mesothelial  appearance  in  sil- 
ver nitrate  preparations. 

In  the  tendons  of  the  tail 
of  the  mouse,  Loevy  describes 
the  cells  as  flat,  rectangular, 
and  rhomboidal;  they  are 
parallel  to  the  long  axis  of 
the  tendon,  two  of  their  sur- 
faces extended  into  flat  plates 
or  wings  which  effect  a  union 
with  'wings'  of  adjacent  cells. 
A  cell  may  have  from  2  to  4 
wings.  The  wings  or  plates 
have  been  interpreted  as  elas- 
tic in  nature,  but  do  not  re- 
act to  specific  stains  for  elas- 
tic tissue.  Each  cell  contains 
a  spherical  or  oval  deeply 
staining  nucleus;  the  nuclei 


c.R. 


FIG.  131. — TRANSVERSE  SECTION  OF  TENDON 
OF  TAIL  OF  ADULT  MOUSE. 

It  consists  of  four  secondary  bundles  or  fas- 
ciculi, s.b.;  p.b.,  primary  bundle;  p.,  epiten- 
dineum;  c.R.,  tendon  cell  (cell  of  Ranvier). 
(After  Loevy,  Anat.  Anz.,  45,  10,  1913.) 


TENDONS 


117 


of  successive  cells  are  often  so  placed  as  to  be  immediately  adjacent.  Ac- 
cording to  Loevy  the  fibrils  are  developed  from  fibroblasts ;  the  definitive 
tendon  cells,  which  form  the  primary  bundles,  arise  from  cells  of  Ran- 
vier.  Both  come  from  mesenchyme  cells,  but  the  fibroblasts  entirely 
disappear,  while  the  cells  of  Ranvier  persist  as  the  characteristic  winged 
tendon  cells. 

Ligaments,  fascia,  and  aponeuroses  are  very 
similar  to  tendon,  but  are  less  compact  and  contain 
more  elastic  tissue. 

Bursae  are  mesothelium-lined  sacs  in  connec- 
tion with  the  large  diarthroses  and  certain  locations 
where  tendons  are  subject  to  friction. 

Tendons  are  supplied  with  blood-vessels  and 
sensory  nerve  endings,  in  a  manner  very  similar  to 
skeletal  muscle. 

The  exact  manner  of  the  attachment  of  striped 
muscle  to  tendon  is  still  disputed.  According  to 
certain  investigators  (0.  Schultze,  Arch.  f.  mikr. 
Anat.,  Bd.  79,  1912),  the  myofibrils  and  tendon 
fibrils  are  directly  continuous  through  the  sarco- 
lemma.  Others  (Baldwin,  Morph.  Jahrb.,  Bd.  45, 
1912)  hold  that  the  muscle  ends  sharply,  remain- 
ing striped  to  its  termination,  and  that  the  rounded 
or  pointed  end  is  completely  enveloped  by  the  sar- 
colemma  (Fig.  132).  The  muscle  fibers  are  de- 
scribed as  being  dovetailed  into  the  tendon,  the  ten- 
don fibrils  being  attached  to  the  sarcolemma.  This 
is  the  more  commonly  accepted  interpretation;  but 
it  seems  probable  that  both  types  of  muscle-tendon 
connections  occur  in  different  muscles,  for  in  cer- 
tain muscles  the  cross  striations  become  gradually 
more  vague  toward  the  tendon,  and  the  point  of 
transition  from  muscle  to  tendon  is  by  no  means  sharply  marked.  More- 
over, the  fact  that  certain  ligaments  and  aponeuroses  arise  normally  by 
transformation  of  muscle  adds  support  to  the  idea  of  muscle-tendon  con- 
tinuity. 

Baldwin  distinguishes  two  general  types  of  muscle  termination  with 
respect  to  tendon :  one  in  which  the  long  axes  of  tendon  and  muscle 
fiber  coincide;  a  second  in  which  they  meet  at  an  angle.  In  neither  type 
does  he  recognize  a  direct  continuity  between  muscle  and  tendon  fibrils. 


FIG.  132. — PORTION 
OF  A  MUSCLE  FI- 
BER FROM  THE  TAIL 
OF  A  5  CM.  FROG 
TADPOLE. 

Each  cone-shaped 
sarcolemma  process 
has  attached  to  it  a 
tendon  fibril.  Two 
of  the  processes  do 
rive  fibrillae  from  a 
large  fibroblastic  cell 
situated  among  the 
tendon  fibrilte.  (Af- 
ter Baldwin.)  xiooo. 


118  MUSCULAE  TISSUE 

In  the  first  type  the  sarcolemma  presents  pointed  ends,  to  which  the  ten- 
don fibrils  are  attached;  in  the  second,  the  sarcolemma  presents  a  flat 
surface  which  rests  directly  against  the  attached  structure,  whether 
fascia,  periosteum,  or  .ligaments.  Lymphatics  are  abundant  in  tendons. 


CHAPTER  V 
NERVOUS   TISSUES 

GENERAL   CONSIDERATIONS 

Nervous  tissue  comprehends  those  tissue  elements  which  are  peculiar 
to  the  nervous  system.  In  the  protoplasm  of  nervous  tissue  proper 
(neuroplasm)  the  fundamental  properties  of  irritability  and  conductivity 
have  become  predominant.  The  nervous  system  includes  the  cerebro- 
spinal — comprising  the  central  (brain  and  spinal  cord)  and  the  periph- 
eral (cerebral  and  spinal  nerves)  portions — and  the  sympathetic  divi- 
sions. For  convenience  we  may  speak  also  of  the  central  and  peripheral 
nervous  systems,  the  latter  including  the  sympathetic  division.  The 
essential  unit  of  structure,  comparable  to  the  cell  of  other  tissues,  is 
here  the  neuron,  or  neurocyte.  A  neuron  is  a  nerve  cell  in  the  broadest 
sense  of  the  term.  It  consists  of  the  cell  body  (nerve  cell  of  the  older 
writers,  cyton),  together  with  all  of  its  processes.  These  latter  are 
divisible  into  two  varieties,  the  axon  and  the  dendrons  (dendrites). 

The  neurons  are  among  the  largest  cells  of  the  body.  Their  cell  body 
is  of  variable  size,  in  some  cases  extremely  minute,  at  other  times 
sufficiently  large  to  be  readily  observed  with  the  unaided  eye.  Their 
processes,  usually  of  considerable  number,  vary  in  length  from  a  milli- 
meter or  less,  up  to  half  the  height  of  man.  It  is  therefore  obviously 
impossible  to  study  microscopically  at  one  time  the  entire  course  of 
these  longer  processes.  This  circumstance  renders  it  advisable  to  retain 
the  term  nerve  fiber  of  the  older  writers  to  designate,  not  as  was  the 
former  conception,  a  histological  entity,  but  rather  that  portion  of  those 
long  processes  of  the  nerve  cell  which  pursues  its  course,  as  a  rule, 
outside  of  the  gray  matter  of  the  central  portion  of  the  cerebrospinal 
division. 

On  this  basis  we  may  divide  the  neuron  into  the  nerve  cell  and  the 
nerve  fiber.  The  former  term  includes  the  cell  body,  or  cyton,  with  its 
dendrons  and  the  proximal  portion  of  its  axon;  the  distal  portion  of 
the  axon  forming  the  essential  part  of  a  long  nerve  fiber.  The  nerve  cells 

119. 


S.L.- 


ax. 


FIG.  133. — DIAGRAM  OF  A  NEURON. 

a  h,  axon  hillock;  o  x,  axon;  c,  cytoplasm,  the  Nissl  granules  have  been  stained; 
d,  dendrons;  ra,  myelin  sheath  of  the  nerve  fiber;  m',  muscle  fiber;  n,  nucleus;  ri, 
nucleolus;  n  of  n,  nucleus  of  the  neurolemmaof  the  nerve  fiber;  n  R,  node  of  Ran- 
vier;  s  /,  collateral;  s  L,  segment  of  Lantermann;  tel,  telodendrion  or  terminal 
arborization  which  here  forms  a  motor  end-plate.  (After  Barker.) 


120 


THE  NERVE  CELL  121 

arc  found  throughout  the  gray  matter  of  the  central  portion  and  in  the 
peripheral  ganglia  of  the  cerebrospinal  division  and  in  the  sympathetic 
ganglia.  Nerve  fibers  occur  in  the  white  matter  of  the  central  portion 
and  in  the  nerve  trunks  and  ganglia  of  the  peripheral  portions  of  the 
nervous  system. 

In  the  peripheral  nervous  system  the  nervous  tissues  are  chiefly 
supported  by  the  connective  tissues,  but  in  the  central  portion  a  special 
form  of  supporting  tissue,  the  neuroglia,  is  also  found.  This  is  de- 
scribed below. 

THE   NERVE    CELL 

(Cyton,  Cell  Body,  Perikaryon,  Ganglion  Cell) 

This  term,  as  already  stated,  includes  the  cell  body  with  its  den- 
drons  and  the  proximal  portion  of  its  long  axon.  The  cell  bodies  vary 
in  size  from  4  /«  to  200  ft  in  diameter.  Their  shape  is  chiefly  dependent 
upon  the  number  of  their  dendritic  processes.  Unipolar  nerve  cells,  with 
but  a  single  process,  are  flask-shaped  or  pyriform;  bipolar  cells,  whose 
processes  are  usually  derived  from  opposite  extremities,  are  most  fre- 
quently fusiform;  multipolar  nerve  cells,  from  the  considerable  number 
of  their  processes,  are  irregularly  stellate. 

Nucleus. — The  cytoplasm  of  the  cell  is  finely  granular  and  contains 
a  large  vesicular  nucleus  which,  as  a  rule,  is  excentrically  situated.  The 
appearance  of  this  large  nucleus  is  quite  characteristic  of  the  nerve  cell 
as  distinguished  from  the  cells  of  other  tissue.  The  nuclear  membrane 
is  distinct  and  highly  chromatic.  The  contents  of  the  nucleus,  however, 
except  for  the  large  spherical  nucleolus  which  is  quite  constantly  present, 
is  noticeably  deficient  in  chromatin.  Those  few  small  karyosomes  which 
are  present  are  mostly  adherent  to  the  inner  surface  of  the  nuclear  mem- 
brane. The  achromatic  nucleoplasm  forms  the  greater  portion  of  the 
nucleus.  Occasionally  the  chromatin  forms  still  finer  granules,  and  is 
more  equally  distributed  throughout  the  nucleus.  A  large,  chromatic, 
centrally  situated  nucleolus  is  nearly  always  present. 

Cytoplasm. — The  finer  structure  of  the  cytoplasm  of  the  nerve  cell 
is  the  subject  of  considerable  difference  of  opinion.  The  studies  of 
Xissl  have  shown  that  it  is  divisible  into  a  substance  which  is  readily 
stained  by  methylene  blue,  thionin,  etc.  (the  stainable  substance  of  Nissl, 
tigroid  of  von  Lenhossek),  and  an  apparently  homogeneous  substance 
which  is  not  so  readily  stained  (the  unstainable  substance  of  Nissl). 


FIG.  134. — A  UNIPOLAR  GANGLION  CELL  OF  A  FROG. 

a,  cell  body;  b,  axon;  c,  dendron.    Methylene  blue.    Highly  magnified.    (After  von 
Smirnow.) 


FIG.  135. — MTJLTIPOLAR  GANGLION  CELL  FROM  THE  VENTRAL  HORN  OF  THE  GRAY 
MATTER  OF  THE  SPINAL  CORD  OF  THE  Ox. 

a,  axon;  b,  dendrons.     (From  Barker,  after  Deiters.) 


122 


THE  NERVE  CELL 


123 


Nissl's  substance,  chromophilic 
or  tigroid  substance,  occurs  in  the 
form  of  flake-like  granules  of  vary- 
ing size  and  irregular  shape.  Their 
disposition  within  the  cytoplasm  is 
subject  to  considerable  variations 
in  different  nerve  cells,  but  accord- 
ing to  Nissl  it  is  fairly  constant  in 
cells  of  the  same  location  for  any 
given  species.  The  amount  also  of 
the  chromophilic  substance  is  sub- 
ject to  variation  depending  upon, 
the  functional  condition  of  the  in- 
dividual. It  has  been  shown  that 
the  substance  is  greatly  diminished 
by  fatigue  (Dolly)  and  after  sur- 
gical shock  (Crile).  In  general 
also,  the  longer  the  axon  the  great- 
er the  amount  of  chromophilic  sub- 
stance. Chemically,  it  is  a  nucleo- 
proteid.  There  is  considerable  his- 
tologic  evidence  to  indicate  that  it 
has  a  nuclear  origin,  appearing 
first  in  the  form  of  'chromidia/ 
and  it  is  accordingly  sometimes 
designated  as  cytochromatin.  Miihl- 
man  has  shown,  however,  that 
tigroid  nuclein  is  soluble  in  weak 
soda  solutions  while  nucleus  nu- 
clein is  not.  It  has  been  suggested 
(Heidenhain)  that  it  may  perhaps 
have  an  accessory  nuclear  function. 
According  to  Held  it  is  present  as 
a  diffuse  continuous  substance,  co- 
agulated in  the  form  of  flakes  and 
granules  in  fixed  tissues. 

Those  nerve  cells  in  which  the 
Nissl  substance  is  abundant  are 
said  to  be  in  a  pyknomorphous, 
those  in  which  it  is  scanty  in  an 


FIG.  136.  —  PYRAMIDAL  MULTIPOLAR 
NERVE  CELL  FROM  THE  CEREBRAL 
CORTEX  OF  A  MOUSE. 

a,  axon;  d,  dendrons;  c,  collaterals. 
Golgi  technic.  (Barker,  after  Ramtfn 
y  Cajal.) 


124 


NERVOUS  TISSUES 


apyknomorphous  condition.    The  Nissl  granules  are  apparently  used  up 
.during  functional  activity  of  the  nerve  cell. 

The  brain-cells  show  a  strong  affinity  for  adrenalin,  the  secretion  of 
the  suprarenal  glands;  this  fact  leads  Crile  (1914)  to  strongly  suspect 
that  the  Nissl  substance  is  a  volatile,  extremely  unstable  combination  of 
certain  elements  of  the  brain-cells  and  adrenalin  because  the  suprarenal 


FIG.  137. — ISOLATED  NERVE  CELLS  FROM  THE  SPINAL  CORD  OF  MAN. 
x,  axon.     Carmin.     X  160.     (After  Sobotta.) 

glands  alone  do  not  take  the  Nissl  stain,  and  the  brain  deprived  of 
adrenalin  does  not  take  Nissl  stain. 

Nissl  substance  disappears  in  case  of  lesion  of  the  neuron,  but  re- 
appears in  abundance  after  temporary  injury  and  recovery  of  the  cell. 
Such  disappearance  after  section  of  the  axon  (axonal  reaction)  is  accom- 
panied by  a  swelling  of  the  neuroplasm  and  the  peripheral  migration  of 
the  nucleus,  after  from  ten  to  fifteen  days. 

Concerning  the  finer  structure  of  the  unstainable  substance  of  Nissl, 
comparatively  little  is  known.  With  varying  methods  of  fixation  this 
portion  of  the  cytoplasm  has  been  found  to  show  very  fine  fibrils  (neuro- 


THE  NERVE  CELL 


125 


fibrils,  Fig.  141)  (Schultze,  Flemming,  Apathy,  Bethe)  and  fine  acidophil 
granules  (neurosomes  of  Held;  probably  mitochondria).  Besides  these 
structures  there  remains  a  homogeneous  ground  substance  or  hyaloplasm, 
which,  though  of  extreme  physiological  importance,  in  the  usual  histo- 
logical  preparations  presents  no  structure.  Centrosomes  and  attraction 
spheres  have  been  frequently  observed  in  the  nerve  cells  of  the  lower 
vertebrates,  and  occasionally  in  those  of 
mammals. 

The  cytoplasm  of  many  nerve  cells  con- 
tains a  characteristic  brownish-yellow  pig- 
ment, whose  fine  granules  have  a  tendency 
to  accumulate  in  the  vicinity  of  the  nu- 
cleus. 

Mitochondria  also  have  been  reported  in 
ganglion  cells  of  the  rabbit  (Schirokogoroff, 
Anat.  Anz.,  43,  19  and  20,  1913).  Cowdry 
(Amer.  Jour.  Anat.,  17,  1,  1914)  describes 
granular  and  rod-like  mitochondria  in  the 
spinal  ganglion  cells  of  a  number  of  verte- 
brates, including  man.  They  are  said  to 
occur  throughout  the  entire  neuron,  axon 
as  well  as  dendrons.  They  are  regarded  as 
fundamental  constituents  of  the  neuro- 
plasm.  It  is  suggested  that  they  are  con- 
cerned with  the  metabolism  of  the  neuro- 
cyte. 

Xeurons  are  incapable  of  division;  de- 
stroyed neurons  cannot  be  replaced;  the  axon,  however,  may  regener- 
ate/ 

End  fibrils  of  other  neurons  have  been  demonstrated  within  the  cyto- 
plasm of  the  nerve  cell.  Apathy  has  likewise  demonstrated  that  fibrils 
occasionally  pass  from  one  neuron  to  another,  so  that  we  no  longer  con- 
sider that  a  neuron,  though  a  structural  unit,  is  in  all  cases  anatomically 
independent  of  all  other  neurons.  The  present  status  of  this  much  dis- 
cussed question  seems  to  be  comparable  to  that  of  the  cell,  as  a  histological 
unit  of  structure,  which  though  formerly  thought  to  exist  independently 
of  other  cell  units,  has  since  been  found  to  be  frequently  connected,  as 
by  the  intercellular  bridges  of  epithelium  and  of  smooth  muscle.  The 
neurons  of  the  nervous  system  therefore,  while  being  usually  related  to 
one  another  by  contiguity  or  by  contact  only,  may  occasionally  be  more 


FIG.  138.— VARIOUS  TYPES  OF 
NERVE  CELLS  OF  THE  CERE- 
BELLAR  CORTEX. 

/,  cell  of  Purkinje;  the  cyto- 
plasm contains  large  flakes  of 
Nissl  substance;  2  and  3,  small- 
er nerve  cells,  'granule  cells.' 
Nissl's  stain.  X  1200. 


S     I 


a,  ^  o 


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P  "r/5     ET  **-" 

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H  §:• 


•326 


THE  NEEVE  CELL 


127 


directly  connected  by  fibrillse,  which  pass  from  the  processes  of  one 
neuron  to  the  cell  body  or  processes  of  a  second  neuron  (Apathy,  Bethe), 
or  by  'concrescence/  as  described  by  Held. 

The  nerve  cells  are  surrounded  by  a  narrow  interval  which  separates 
them  from  the  surrounding  tissue.  This  is  presumably  a  lymphatic  or 
tissue  fluid  space.  Holmgren  has  demonstrated  also  the  presence,  within 
the  cytoplasm  of  the  nerve  cell,  of  minute  canaliculi  which  form  an  intra- 


FIG.  140. — A  NERVE  CELL  FROM  THE  TRAPEZOID  NUCLEUS  IN  THE  MIDBRAIN  OF  A 

RABBIT. 

o,  axon;  b,  axons  of  other  nerve  cells  which  terminate  in  relation  and  apparently 
fuse  with  the  cytoplasm  of  the  cell  body;  c,  points  of  fusion  or  zones  of  concrescence; 
d,  dendrons  which  have  been  cut  off  close  to  the  cell  body;  e,  neuroglia.  The  cyto- 
plasm shows  a  neurofibrillar  network  and  Nissl  granules.  Iron  hematoxylin.  Very 
highly  magnified.  (After  Held.) 


cellular  network,  more  abundant  near  the  surface  of  the  cell,  and  which 
he  has  termed  juice  canaliculi,  or  trophospongium.  These  canaliculi 
may  possibly  account  for  the  peculiar  intracellular  network  which  Golgi 
has  demonstrated  in  the  periphery  of  the  nerve  cell,  by  a  modification  of 
his  rapid  silver  impregnation  method. 

The  processes  of  the  nerve  cell  are  of  two  varieties :  the  one,  broad, 
granular,  and  rapidly  dividing  in  the  vicinity  of  the  cell  body  into  a 
number  of  branching  subdivisions,  is  the  ilendron;  the  other,  long,  slen- 
der, and  finely  but  distinctly  fibrillar,  arises  from  the  cell  body  direct,  or 


128 


NERVOUS  TISSUES 


Fia.  141. — A  NEURON  (GIANT  PYRAMI- 
DAL CELL,  OR  CELL  OF  BETZ)  FROM 
THE  CEREBRAL  CORTEX  OF  MAN, 
SHOWING  THE  NEUROFIBRILS. 

Bielschowsky  technic.     X  500. 


from  the  base  of  a  dendron,  and  passing  for  a  considerable  distance  from 
the  cell  body,  finally  enters  the  nerve  fiber  as  its  axis  cylinder,  or  termi- 
_  nates    in   relation   to   some    distant 

JjL  ^^^         nerve  cell.    This  latter  process  is  the 

^^.  Jliii^gi-^&ffi  axon.     Each  cell  body  usually  pos- 

^^^bdfflH  ^^^^^     sesses  a  single  axon  and  several  den- 

||8J|pF  drons.     Cells  without  an  axon  are 

^^iH         ^Bar"'  found  in  the  retina  and  in  the  ol- 

factory bulb;  except  for  these,  all 

J$$jjjS&XJI  nerve  cells  in  the  body  of  man  pos- 

^ispf  sess  an  axon  and  usually  but  one 

such  process.  The  subdivision  of 
nerve  cells  into  uni-,  bi-,  and  multi- 
polar  cells  is,  therefore,  chiefly  based 
upon  the  number  of  their  dendrons. 
Dendrons  (Dendrites,  Protoplas- 
mic Processes}. — The  dendrons  of  a 
nerve  cell  vary  from  one  to  a  consid- 
erable number.  They  arise  from  the  cell  body  by  a  broad  stem,  and 
quickly  break  into  branches  which  can  be  traced  for  a  considerable  dis- 
tance— in  fact,  the  arborization  of  the  dendrons  is  usually  so  extensive 
that  it  can  be  followed  for  only  a  short  portion  of  its 
course.  Occasionally  dendrons  do  not  branch  until 
they  have  arrived  at  a  considerable  distance  from 
their  parent  cell-body. 

The  structure  of  the  dendron  is,  to  all  appear- 
ances, similar  to  that  of  the  cell-body.  The  chromo- 
philic  substance  is  continued  for  some  distance  into 
the  arborizing  dendrons,  which  often  possess  a  finely 
fibrillar  appearance.  In  Golgi-stained  preparations 
the  dendrons  frequently  present  a  thorny  appearance, 
due  to  the  clustering  along  their  borders  of  minute 
lateral  projections,  the  gemmules. 

The  terminal  filaments  of  the  dendronic  arboriza- 
tion are  frequently  in  relation  with  the  cell  bodies 
or  axons  of  other  neurons,  less  frequently  with  the 
dendrons  of  other  neurons.  Such  contact  relation- 
ship is  known  as  synapsis. 

Dendrons  are  cellulipetal  processes,  transmitting  impulses  to  the  cyton. 
The  Axon  (Neuraxis,  Neuraxon,  Neurite,  Axis  Cylinder  Process}. — 


FIG.  142.  — INTRA- 
CELLULAR  NET- 
WORK (TROPHO- 
SPONGITJM) 

WITHIN     A      PUR- 

KINJE  CELL  OF 
THE  CEREBELLUM 
OF  Strix  flam- 
mea. 

Golgi's  stain.  (After 
Golgi.) 


THE  NEKVE  CELL 


129 


This  process  in  contradistinction  to  the  dendron,  is  long  and  slender,  as 
a  rule  does  not  arborize  near  its  parent  cell-body,  is  of  smooth  and  regular 
contour  in  Golgi  preparations,  and  contains  no  chromophilic  substance. 
It  arises  from  the  cell  body,  or  less  frequently  from  the  base  of  a  dendron, 
by  a  conical,  clear  area,  the  axon  hillock  or  implantation  cone,  which, 
like  the  process  itself,  is  devoid  of  chromophilic  granules.  It  consists  of 


FIG.  143.— GOLGI  CELL,  TYPE  I. 
c,  collaterals;  n,  axon.     Golgi's  stain.     (After  Kolliker.) 

a  bundle  of  delicate  neurofibrils  (axon  fibrils)  embedded  in  axoplasm. 
During  early  developmental  stages  the  fibrils  increase  in  number  by  a 
splitting  of  preexisting  fibrils. 

At  some  little  distance  from  the  parent  cell-body  the  axon  gives  off 
very  fine  lateral  branches,  the  collaterals,  which  leave  the  parent  stem 
at  the  nodes  of  Ranvier  at  nearly  right  angles.  These  delicate  branches, 
as  also  the  axon  proper,  finally  terminate  by  a  sudden  end  arborization, 
or  telodendrion,  by  which  each  axon  is  placed  in  relation  with  a  large 


130 


NEEVOUS  TISSUES 


number  of  neurons,  or  a  considerable  area  of  surface.  The  telodendrion 
may  terminate  in  minute  knobs  or  plates,  the  neuropodia.  The  teloden- 
drion is  structurally  apparently  an  efficient  mechanism  for  mediating 


FIG.  144. — GOLGI  NERVE  CELL,  TYPE  II. 
a,  axon;  x,  dendron.     (After  Kolliker.) 

the  phenomenon  of  'axon  reflex'  (Langley).  The  parent  stem  of  the  axon 
may  be  finally  exhausted  in  its  collaterals,  or  it  may  in  turn  end  in  a 
terminal  arborization.  Collaterals  are  said  to  be  more  frequent  in  the 
proximal  than  in  the  distal  portion  of  the  axon.  The  axon  transmits 
impulses  away  from  the  cell-body;  it  is  a  cellulifugal  process. 


THE  NERVE  FIBEE  131 

According  to  the  length  of  their  axons,  neurons  are  divided  by  Golgi 
into  two  types. 

1.  Golgi  cells,  Type  I  (Deiters'  cells). 

2.  Golgi  cells,  Type  II   (Golgi's  cells). 

The  cells  of  Type  I  possess  a  long  axon  which  passes  beyond  the  con- 
fines of  the  gray  matter  in  which  it  arises  and  usually  becomes  the  axis 
cylinder  of  a  nerve  fiber. 

The  cells  of  Type  II  possess  a  short  axon  which  forms  its  terminal 
arborization  in  the  vicinity  of  its  parent  cell-body.  The  cells  of  this  type 
are  usually  association  and  commissural  neurons;  they  place  in  conduc- 
tion relation  other  not  very  remote  neurons.  The  cells  of  Type  I,  on  the 
other  hand,  are  more  frequently  projection  neurons ;  they  are  distributed 
from  the  nerve  centers  to  other  and  perhaps  very  different  tissues,  their 
courses  lying  in  the  long  projection  tracts  and  nerve  trunks  of  the 
nervous  system. 

The  cells  of  Type  II  are  therefore  most  frequently  intrinsic  or  endog- 
enous neurons,  their  whole  course  lying  in  one  division  of  the  central 
nervous  system,  e.g.,  the  gray  matter  of  the  spinal  cord.  The  cells  of 
Type  I  are  more  frequently  extrinsic  or  exogenous;  they  arise  in  one 
part  of  the  nervous  system  to  be  distributed  to  a  distant  portion,  e.g., 
they  arise  in  the  peripheral  ganglia  and  enter  the  spinal  cord  to  terminate 
in  its  gray  matter,  or  vice  versa. 

The  size  of  a  nerve  cell  is  thought  to  bear  a  general  relation  to  the 
length  of  its  axon,  the  larger  cells  possessing  the  longer  axons.  The 
cells  of  Golgi's  Type  I  are  therefore  larger  than  those  of  Type  II.  Like- 
wise the  cells  of  the  motor  tracts,  whose  axons  are  as  a  rule  much  longer 
than  those  of  the  sensory  tracts,  are  characterized  by  their  large  size 
as  compared  with  the  sensory  cells. 


THE   NERVE    FIBER 

The  origin  of  the  nerve  fiber  and  its  relation  to  the  other  portions 
of  the  neuron  will  be  appreciated  by  tracing  the  course  of  the  axon  of  a 
motor  nerve  cell  of  the  ventral  horn  of  gray  matter  in  the  spinal  cord. 
This  process,  arising  in  the  central  gray  matter,  is  at  first  a  naked  axon. 
It  soon  leaves  the  gray  matter  to  traverse  the  white  matter  and  makes  its 
exit  from  the  spinal  cord  as  the  axis  cylinder  of  one  of  the  fibers  of 
a  ventral  nerve  root.  On  leaving  the  gray  matter  the  axon  acquires  a 


132  NEEVOUS  TISSUES 

cylindrical  sheath  of  myelin  substance,  the  medullary  sheath,  myelin 
sheath,  or  white  substance  of  Scliwann. 

On  entering  the  ventral  nerve  root,  which  lies  outside  of  the  white 
matter  of  the  spinal  cord,  the  axon  receives  an  epithelioid  membranous 
sheath,  the  neurolemma  or  nucleated  sheath  of  Scliwann.  The  axon 
retains  these  two  sheaths  until  near  its  termination,  when  the  sheaths 
suddenly  stop,  the  axon  becoming  again  naked  as  it  breaks  into  terminal 
fibrils. 

Not  all  nerve  fibers  are  medullated,  nor  do  they  all  possess  a  neuro- 
lemma. The  axons  of  the  central  nervous  system  are  not  supplied  with 
a  neurolemma  until  they  pierce  the  meninges  to  enter  the  nerve  roots. 
Those  of  the  gray  matter  also  have  no  appreciable  medullary  sheath.  The 
axons  of  the  peripheral  nerve  trunks  and  ganglia  are  all  supplied  with  a 
neurolemma  except  at  their  terminals,  as  already  explained.  Yet  some 
of  the  peripheral  axons  have  a  medullary  sheath,  while  others  have  none. 
An  axon  with  its  enveloping  sheaths  constitutes  a  nerve  fiber,  and  upon 
the  presence  or  absence  of  these  sheaths  nerve  fibers  may  be  classified  as 
follows : 

,r  -i  n  A  i  fl.     With  a  neurolemma 

A.  Medullated  nerve  fibers -i  _      ,TT. . , 

|2.     Without  a  neurolemma. 

B.  Non-medullated  nerve   f  3.     With  a  neurolemma 

fibers.  1  4.     Without  a  neurolemma — alemmal. 

1.  Medullated  Nerve  Fibers  with  a  Neurolemma, — Nearly  all  the 
nerve  fibers  of  the  cerebrospinal  nerve  trunks  and  ganglia  and  some  of 
those  of  the  sympathetic  nerves  are  of  this  type.  These  nerve  fibers 
consist  essentially  of  three  cylindrical  structures :  the  axis  cylinder,  which 
is  the  continuation  of  the  axon  of  a  nerve  cell,  and  which  forms  the  cen- 
tral portion  or  core  of  the  nerve  fiber;  the  medullary  sheath,  which 
forms  a  hollow  cylinder  inclosing  the  axis  cylinder,  and  which 
suffers  frequent  interruptions,  as  will  be  described ;  and  the  neurolemma, 
which  is  an  extremely  thin  investing  sheath  forming  an  uninterrupted 
envelope  from  the  point  where  the  nerve  fiber  leaves  the  central  nervous 
system  to  a  point  near  the  end  of  the  fiber  where  the  axis  cylinder  breaks 
into  its  terminal  fibrils.  To  these  structures  an  investing  sheath  of  con- 
nective tissue,  the  sheath  of  Henle,  is  sometimes  added.  It  is  derived 
from  the  connective  tissue  endoneurium  in  which  the  nerve  fibers  are 
embedded.  It  serves  to  support  the  capillary  blood-vessels  destined  for 
the  supply  of  the  nerve  fibers. 

THE  Axis  CYLINDER. — The  axis  cylinder  presents  a  finely  fibrillar 


THE  NERVE  FIBEB 


133 


structure.  The  nature  of  these  fibrils  is  not  well  understood.  They  are 
apparently  continuous  with  the  neurofibrillar  network  of  the  cell  body. 
In  certain  nerve  fibers  of  the  lower  animals  these  fibrils  have  a  ten- 
dency to  collect  into  the  center  of  the  axis  cylinder,  leaving  a  peripheral 
clear  zone;  this  distribution  is  especially  characteristic  of  those  fibers 


FIG.  145. — ISOLATED  NERVE  FIBERS  FROM  A  FROG. 

The  axis  cylinders,  the  enveloping  myelin  sheaths,  and  the  nodes  of  Ranvier  are 
clearly  shown.    Intra-vitam  methylene  blue  stain.     (Barker,  after  von  KoUiker.) 

which  are  not  supplied  with  a  medullary  sheath.  In  mammals,  however, 
the  fibrillae  occupy  a  larger  portion  of  the  axis  cylinder,  the  clear  peri- 
pheral area  being  correspondingly  diminished  until  in  man  it  can  scarcely 
be  recognized.  The  fibrils  of  the  lower  animals  are  also  coarser. 

Apathy,  studying  chiefly  the  lower  animals,  has  considered  these  'ulti- 
mate fibrillce'  to  be  the  conducting  element  of  the  nerve  fiber.  Others, 
however,  lay  greater  stress  upon  the  intervening  clear  portion,  the 


134 


NERVOUS  TISSUES 


FIG.  146. — A  SMALL  PORTION  OF  A  TRANSECTION 

OF  THE  SCIATIC  NERVE  OF  A  DOG. 
.Nerve  fibers   are  seen   in   transection;   their 
myelin  sheaths  are  black,   their  neuraxes  un- 
stained.   Osmium  tetroxid.    Photo.    X  700. 


neuroplasm  of  Schiefferdecker  or  aacoplasm,  as  containing  the  active 
conducting  substance  of  the  fiber. 

According  to  Verworn,  Lenhossek  and  R.  Goldsehmidt,  these  elemen- 
tary fibrillae  (axon  fibrils)   in  the  axis  cylinder  are  nothing  else  than 

skeletal  substance  for  the 
support  of  the  semi-fluid 
neuroplasm.  The  circum- 
stance that  many  of  the 
fibrils  of  an  axis  cylinder 
may  be  sectioned  without 
diminution  of  the  maximum 
effect  of  stimulation  favors 
the  view  that  the  neuro- 
plasm is  the  essential  con- 
ducting substance. 

Tashiro  has  demon- 
strated that  a  living  nerve 
gives  off  a  definite  amount 
of  carbon  dioxid,  and  that 

when  the  nerye  is  stimulated  the  amount  of  carbon  dioxid  production  is 
increased.  He  conceives  of  the  propagation  of  nerve  impulses  as  a  chemi- 
cal change,  the  propagation  being  in 

essence  a  restoration  of  equilibrium  —  Nk 

in  the  nerve  fiber  disturbed  at  the      ''^ ''-,•• 
point  of  contact. 

The  axis  cylinder  is,  under  certain 
conditions  at  least,  found  to  be  in- 
closed by  an  extremely  delicate  mem- 
brane, the  axolemrna  of  Kiihne.  The 
existence  of  this  membrane  as  an  in- 
tegral part  of  a  living  axis  cylinder 
has  been  denied  by  others.  It  may 
be  simply  a  fixation  artifact. 

THE  MEDULLARY  SHEATH  (White 
Substance  of  Schwann,  Alyelin 
Sheath).  —  The  medullary  sheath 
forms  a  cylindrical  investment  for  the 
axis  cylinder.  Medullated  fibers  vary 

greatly  in  diameter  according  to  the  amount  of  myelin  present.  It 
appears  to  be  retained  in  position  by  the  neurolemma,  for  when  the 


FIG.  147. — A  GROUP  OF  LARGE  MED- 
ULLATED  FlBERS  FROM  A  NERVE  IN 
THE  PERITRACHEAL  AREOLAR  TIS- 
SUE OF  THE  CAT. 

Ax,  axis  cylinder;  Nk,  neurokeratin 
framework;  Nc,  neurolemma  cell  and 
nucleus;  M,  medullary  sheath;  N, 
neurolemma.  X  1000.  ' 


THE  NERVE  FIBER 


135 


latter  is  ruptured  the  myelin  exudes 
in  the  form  of  'myelin  drops.'  The 
myelin  thus  obtained  possesses  the 
physical  properties  of  a  fat.  It  is 
also  capable  of  being  blackened  by 
osmium  tetroxid.  By  extraction  with 
ether  the  myelin  can  be  removed,  leav- 
ing behind  a  supporting  framework 
of  neurokeratin.  The  function  of 
inyeliu  is  probably  nutritive,  though 
it  has  been  regarded  as  an  insulating 
substance.  It  is  thought  to  be  present 
in  small  amounts  even1  in  so-called 
non-medullated  fibers.  It  seems  rea- 
sonable to  suppose  that  it  may  have 
a  double  function,  that  is,  nutritive 
and  in  part  insulating. 

At  frequent  intervals  in  the  course 
of  the  nerve  fiber  its  myelin  sheath 
suffers  complete  interruption,  thus 
forming  the  annular  constrictions  or 
nodes  of  Ranvier.  At  these  points  the 
neurolemma  dips  in  until  it  is  in  con- 
tact with  the  axis  cylinder.  Both  axis 
cylinder  and  neurolemma  are  contin- 
ued past  the  node  without  interrup- 
tion. 

The  successive  nodes  of  Ranvier 
divide  the  nerve  fiber  into  internodal 
segments.  Within  each  internodal 
segment  the  medullary  sheath,  on 
blackening  with  osmium  tetroxid, 
presents  clear  intervals  which  pene- 
trate the  myelin  sheath  ic  such  man- 
ner as  to  give  the  appearance  of 
obliquely  disposed  clear  lines  or  inci- 
sions. These  incisures  of  Schmidt 


B 


FIG.  148.— NERVE  FIBERS. 

A  and  B,  from  the  sciatic  nerve  of  a 
rabbit,  isolated  by  teasing,  and  viewed 
in  profile;  C,  a  group  of  nerve  fibers  in 
transection,  from  the  sciatic  nerve  of 
a  dog.  a,  axon;  b,  neurolemma  pro- 
jecting beyond  the  torn  end  of  the 
fiber;  d,  nucleus;  h,  endoneurium  or 
fibrous  sheath  of  Henle;  I,  Schmidt- 
Lantermann  lines;  n,  nodes  of  Ran- 
vier. Osmium  tetroxid.  A  and  B, 
X  670;  C,  X  900. 


(Schmidt-Ijdntermann     lines)     have 

not  been  satisfactorily  explained  and  can  not  be  demonstrated  in  the 
living  fiber,  yet  they  present  a  constant  form  and  are  always  present  in 
10 


136 


NERVOUS  TISSUES 


osmic  preparations.  These  iiicisures  subdivide  the  interannular  segments 
of  the  medullary  sheath  into  medullary  segments.  Schmidt  originally 
considered  them  to  be  the  optical  expression  of  folds  in  the  outer  fibrous 
coats.  Lantermann  and  others  claim  to  have  shown  that  they  are  within 
the  neurolemma.  They  are  believed  by  others  to  represent  the  limits  of 
cones  of  neurokeratin.  The  incisures  may  point  in  different  directions. 
They  are  more  probably  artifacts,  representing  fractures  in  the  delicate 
myelin  sheaths. 

In  preparations  of  fresh  nerve  fibers  which  have  been  treated  with 
silver  nitrate  according  to  the  method  of  Banvier,  the  solution  is  found 

to  enter  the  fiber  most  readily 
at  the  nodes  of  Ranvier,  so  that 
if  blackened  by  exposure  to  the 
sunlight,  minute  -{--like  appear- 
ances are  seen  at  each  node.  By 
prolonged  maceration  in  weak 
solutions  of  silver  nitrate  the  so- 
V  lution  penetrates  still  farther 

FIG.  149. — CROSS  AND  LONGITUDINAL  SEC- 
TIONS OP  THE  SAME  FUNICULUS  (N) 
OF  NON-MEDULLATED  NERVE  FlBERS 
(TURNED  UP  AT  THE  LEFT),  SHOWING 
THE  PERINEURIUM  (P)  AND  THE  RELA- 
TIONSHIP OF  THE  NEUROLEMMA  NUCLEI 
TO  THE  Axis  CYLINDER  BUNDLES  OF 
NEUROFIBRILS. 


From  the  peritracheal  areolar  tissue  of 
the  cat.     X   1500. 


and  the  "blackened  axis  cylinder 
is  found  to  possess  spiral  trans- 
verse markings  which  are  quite 
characteristic.  The  true  mean- 
ing of  these  appearances  has  not 
been  satisfactorily  explained. 
Because  of  the  apparent  greater 
permeability  of  the  fiber  at  these 
points,  these  peculiarities  have 

been  taken  to  indicate  a  certain  relation  of  the  annular  constrictions  to 
the  nutrition  of  the  fiber. 

THE  NEUROLEMMA  (Nucleated  Sheath  of  Scliwann). — The  neuro- 
lemma is  the  outermost  of  the  nerve  fiber  sheaths.  It  is  of  ectodermal 
origin  and  makes  its  appearance  prior  to  the  medullary  sheath.  It 
forms  a  very  delicate  membrane,  which  incloses  the  myelin  substance, 
and  at  each  node  of  Ranvier  com^s  into  contact  with  the  axis  cylinder. 
Attached  to  the  inner  surface  of  the  neurolemma  in  each  internode, 
and  usually  but  one  for  each  internodal  segment,  is  an  oval  nucleus. 
The  nucleus  is  surrounded  by  a  minute  amount  of  finely  granular  cyto- 
plasm. This  structure  is  taken  to  indicate  that  the  embryonal  neuro- 
lemma is  formed  by  cells  which  became  spread  out  over  the  surface  of 
the  primitive  fiber,  one  cell,  as  a  rule,  supplying  each  internodal  segment ; 


THE  NERVE  FIBER 


137 


and  its  nucleus  with  a  minute  amount  of  undifferentiated  protoplasm  is, 
according  to  this  hypothesis,  considered  to  remain  as  a  permanent  part 
of  the  neurolemma. 

2.  Medullated  Nerve  Fibers  without  a  Neurolemma.— This    type 
of  nerve  fiber  composes  the  white  matter  of  the  central  nervous  system. 
The  axis  cylinder  does  not,  of  course,  differ  in  the  least  from  those  of 
the  previous  variety  and  will  need  no  further  description. 

The  medullary  sheath 
also  is  similar  in  its  finer 
structure  to  that  of  the 
previous  type,  hut  since 
no  neurolemma  is  pres- 
ent, these  fibers  possess 
no  nodes  of  Eanvier.  The 
medullary  sheath  of  the 
fibers  found  in  the  white 
matter  of  the  brain  and 
spinal  cord,  is  therefore 
uninterrupted.  Its  sur- 
face is  in  direct  contact 
with  the  neuroglia  net- 
work, which  forms  the 
supporting  tissue  of  these 
organs,  the  innermost 
layer  being  condensed 
into  a  membrane  which 
simulates  a  neurolemma. 
These  fibers  are  accom- 
panied by  sheath  cells 

(Hardesty),  homologues  of  the  neurolemma  cells  of  other  fibers,  which 
aid  in  the  formation  and  maintenance  of  the  myelin. 

3.  Non-medullated  Nerve  Fibers  with  a  Neurolemma     (Sympa- 
thetic Nerve  Fibers,  Remak's  Fibers). — The  most  of  the  fibers  of  the 
sympathetic  division  are  of  this  type.    The  axis  cylinder  does  not  differ 
from  that  of  the  previous  types.     The  medullary  sheath  is  entirely  ab- 
sent or,  at  most,  only  slightly  developed  in  these  fibers.     The  neuro- 
lemma is  perhaps  incomplete  at  times,  but  exhibits  frequent  nuclei 
along  the  course  of  the  fiber.    The  neurolemma  nuclei  appear  to  be  em- 
bedded in  the  superficial  portion  of  the  axis  cylinder.     Fibers  of  this 
type  are  of  quite  frequent  occurrence  also  in  the  cerebral    (cephalic; 


FIG.  150.  —  CROSS-SECTION  OF  THE  TRUNK  OF  THE 
HUMAN  VAGUS  NERVE,  SOME  DISTANCE  BELOW 
THE  NODOSE  GANGLION,  SHOWING  MEDULLATED 
AND  NON-MEDULLATED  FIBERS. 

Pyridin-silver.     X  680.     (After  Ranson.) 


138 


NERVOUS  TISSUES 


cranial)  nerves  of  the  cerebrospinal  division.  Other  cerebrospinal  nerve 
fibers  lose  their  medullary  sheath  and  finally  also  their  neurolcmma 
prior  to  their  termination. 

The  recent  work  of  Kanson  has  shown  that  even  in  the  typical  medul- 
lated  spinal  and  cerebral  nerves  non-medullated  fibers  are  very  abundant. 
f  In    the    vagus    of   the    dog,    for 

example,  the  non  -  medullated 
fibers  actually  preponderate  be- 
low the  diaphragm.  Eanson 
states  that  of  these  no  consid- 
erable portion  can  be  of  sympa- 
thetic origin  and  that  only  a  few 
represent  medullated  fibers  which 
have  lost  their  myelin  distally. 
The  non-medullated  fibers  of  the 
vagus  are  said  to  comprise  both 
afferent  and  efferent  fibers,  the 
latter  arising  from  cells  in  the 
ganglia  (jugular  and  nodose) 
connected  with  the  vagus  nerve 
(Anat.  Rec.,  24,  1,  1914).  The 
spinal  nerves  also  are  shown 
to  contain  more  non-medullated 
than  medullated  fibers  (Amer. 


FIG.  151. — SUCCESSIVE  STAGES  m 
THE  DEGENERATION  PROCESS  EX- 
HIBITED BY  THE  DISTAL  STUMP 
OP  A  MEDULLATED  AXON  (FROM 
SCIATIC  NERVE  OF  ADULT  DOG) 
FOLLOWING  SECTION. 
(1)  on  the  second  day.   (2)  on  the 
fourth  day,  the  two  fibers  a  and  b 
are  at  different  stages  of  degenera- 
tion, the  neurolemma  can  be  seen 
bounding     the     unstained     myelin 
sheath.     (3)  on  the  eighth  day,  the 
fragmented  axon  is  surrounded  by 
an  elliptical  segment  of  myelin  (a). 
(4)  on  the  nineteenth  day,  a,  nu- 
cleus, 6,  droplet  of  myelin  containing 
fragments  of  axon.    (Hanson,  Jour. 
Comp.  Neur.,  22,  6,  1912.) 


Jour.  Anat.,  12,  1,  1911). 

4.    Non-medullated  Nerve 
Fibers  without  a  Neurolemma. 

— These  fibers  are  naked  axis 
cylinders  and  as  such  are  found 
at  the  cytoproximal  end  of  the 
axon  in  the  gray  matter  of  the 
central  nervous  system,  and  at 
the  cytodistal  end  prior  to  the 
termination  of  the  axon  in  its 


arborization  of  terminal  fibrils. 

In  man  nerve  fibers  are  of  this  type  throughout  their  entire  course  only 
in  the  olfactory  nerves. 

All  portions  of  the  neuron,  its  axon  and  collaterals  as  well  as  its 
dendrons,  are  dependent  upon  the  cell  body  for  nutrition ;  hence  each  nerve 
cell  becomes  the  so-called  trophic  center  for  all  of  its  processes. 


THE  NERVE  TIBER 


139 


The  entire  nervous 
system  may  be  considered 
as  an  enormous  tangle, 
formed  by  the  interlacing 
processes  of  an  innumer- 
able number  of  neurons 
whose  complex  fiber  paths 
place  all  portions  of  the 
body  in  communication 
with  all  other  portions. 

Nerve  cells  are  un- 
equally distributed 
throughout  the  central 
division  of  the  nervous 
system;  they  therefore  *c- 
cur  in  more  or  less  dis- 
tinct groups  or  nuclei, 
from  each  cell  of  which 
an  axon  is  frequently  dis- 
tributed along  the  same 
path.  The  larger  bundles 
thus  formed  are  called 
funiculi,  fasciculi,  or  fiber 
bundles;  the  smaller  ones 
tracts. 

Since  each  fiber  of 
such  a  tract  is  dependent 
for  nutrition  upon  the 
nerve  cell  from  which  it 
arises,  the  tract  as  a 
whole  must  depend  upon 
its  nucleus  of  origin  for 
its  nutrition.  Each  nu- 
cleus therefore  becomes 
the  trophic  center  for  the 
fiber  tract  to  which  it 
gives  origin. 

It  may  be  readily 
demonstrated  that  if  any 
such  group  of  axons  be 
cut  or  otherwise  separated 
from  its  trophic  center, 
that  tract  will  promptly 


FIG.  152. — REGENERATIVE  STAGES  IN  THE  PROXIMAL 
STUMP  OF  THE  CUT  SCIATIC  NERVE  OF  THE  DOG, 
SEVERAL  MILLIMETERS  ABOVE  THE  LEVEL  OF 
SECTION. 

p,  toward  the  periphery;  c,  toward  the  center. 
(1)  on  the  nineteenth  day  after  section;  a,  point  in 
the  old  medullated  axon  from  which  arises  an 
extremely  short  branch  which  at  once  divides 
into  two.  (2)  on  the  twenty-fifth  day.  (3)  five 
protoplasmic  strands  down  which  a  new  axon 
is  growing.  (Ranson.)  (Pyridin-silver  prepara- 
tions.) 


140  NERVOUS  TISSUES 

degenerate.  If  these  axons  happen  to  be  the  axis  cylinders  of  medullated 
nerve  fibers,  as  is  often  the  case,  their  myelin  sheaths  become  rapidly 
altered  in  composition  and  acquire  a  tendency  to  disintegrate  into  small 
globular  granules,  which  stain  deeply  with  osmic  acid  when  used  according 
to  the  method  of  Marchi.  For  the  experimental  demonstration  of  this 
form  of  partial  cell  death  occurring  in  that  portion  of  the  neuron  which 
has  been  cut  off  from  its  cell  of  origin,  we  were  originally  indebted  to 
the  eminent  English  physiologist  Waller;  the  resulting  changes  are  there- 
fore called  Wallerian  degeneration. 

Obviously  that  portion  of  a  neuron  or  of  a  fiber  tract  which,  after 
injury  or  disease  involving  its  path,  still  retains  its  connection  with  its 


t 


FIG.  153. — TRANSECTION  OF  THE  SPINAL  CORD  OF  AN  EMBRYO  CHICK. 
c.  rod.  ant.,  axons  to  the  ventral  roots;  c.  rod.  post.,  axons  to  the  dorsal  roots; 
col,  collateral  from  an  axon  back  to  the  gray  matter;  gg,  dorsal  root  ganglion;  roc.  ant., 
ventral  root;  roc.  post.,  dorsal  root.    (After  van  Gehuchten.) 

cell  body  or  trophic  center,  will  not  degenerate.  This  part  of  the  neuron  is 
called  its  central  portion,  in  contradistinction  to  its  distal  portion,  the  latter 
of  which  has  been  severed  from  its  trophic  center  and  is  consequently 
degenerated. 

To  the  study  of  the  various  types  of  Wallerian  degeneration  we  are 
indebted  for  many  of  the  facts  by  means  of  which  the  intricate  tangles  of 
axons  composing  the  various  fiber  tracts  of  the  central  nervous  system 
have  been  partially  unraveled. 

The  contiguous  relationship  of  different  neurons  within  the  nervous 
system  occurs  in  any  one  of  several  ways.  The  terminal  arborizations  or 
telodendrions  of  one  neuron  may  interlace  with : 

a.  the  telodendrions  of  axons  belonging  to  other  neurons, 

b.  the  telodendrions  of  collaterals  of  other  neurons, 

c.  the  dendrons  of  other  neurons,  or 

d.  the  terminal  arborization  may  surround,  basket-like,  the  cell 

body  of  other  neurons. 


NEUROGLIA 


141 


NEUROGLIA 

Both  the  gray  and  the  white  matter  of  the  central  nervous  system 
contain  a  peculiar  supporting  tissue,  the  neuroglia,  which  consists  of 
two  elements,  the  glia  cells  and  the  glia  filers.  The  latter  are  very 
probably  produced  by  the  glia  cells,  of  which  they  were  formerly  con- 
sidered to  be  processes.  They  consist  of  a  substance  similar  to,  perhaps 
identical  with,  the  neurokeratin  framework  of  myelin. 

The  Glia  Cells. — The  glia  cells,  as  seen  in  Golgi  preparations,  are 
divisible  into  two  distinct  types,  the  ependyma  cells  and  the  astrocytes. 

The  EPENDYMA  CELLS  may 
be  considered  as  undifferen- 
tiated  relics  of  the  embryonal 
cells,  from  which  both  glia  and 
true  nerve  or  ganglion  cells 
were  developed.  These  cells 
line  the  central  canal  of  the 
spinal  cord  and  the  ventricles 
of  the  brain,  in  which  latter 
organ  they  also  form  the  cover- 
ing or  outer  coat  of  the  telau 
choroideae. 

The  ependyma  consists  of 
long  nucleated  columnar  cells 
whose  free  ends,  in  fetal  and 


FIG.  154. — TRANSECTIQN  OF  THE  SPINAL  CORD 
OF  A  CHILD,  FIFTH  LUMBAR  SEGMENT. 

The  central  H-shaped  gray  substance  con- 
sists of  nerve  cell  bodies,  dendrons,  non-medul- 


lated  portions  of  axons,  and  neurogliar  sup- 
porting tissue.  The  enveloping  white  sub- 
stance consists  of  medullated  axons  supported 
by  neuroglia.  Weigert  stain.  X  7. 


early  life,  carry  a  tuft  of  cilia ; 
in  adult  life  they  are  usually 
non-ciliated.  The  attached  ends 
of  these  cells  are  embedded 

in  the  surrounding  gelatinous  tissue,  and  are  frequently  prolonged  for 
some  distance  as  a  fine  branched  process.  In  this  way  the  ependyma  of 
the  spinal  cord  enters  into  the  formation  of  the  central  gelatinous  sub- 
stance, in  which  the  branched  processes  of  its  cells  ramify  in  a  glia-like 
manner.  In  the  fetus  the  filamentous  processes  extend  from  the  central 
canal  all  the  way  to  the  periphery  of  the  spinal  cord.  In  the  adult  the 
ependyma  cells  are  prone  to  so  multiply  as  to  almost  occlude  the  central 
canal;  their  processes  have  apparently  become  shorter,  and  now  reach 
the  surface  of  the  spinal  cord  only  at  its  dorsal  median  sulcus. 

The  ASTROCYTES,  when  stained  by  the  Golgi  method,  apparently  con- 
sist of  a  small  cell  body  and  an  innumerable  number  of  long  slender 


FIG.  155. — PORTION  OF  GRAY  SUBSTANCE  FROM  THE  ANTERIOR  HORN  OF  THE  SPINAL 
CORD  OF  MAN,  SHOWING  NERVE  CELL  BODIES,  DENDRONS,  MEDULLATED  AND 
NON-MEDULLATED  PORTIONS  OF  AXONS,  AND  NKUROGLIA. 
(From  Salinger,  after  Kolliker.) 


FIG.  156. — TRANSVERSE  SECTION  THROUGH  THE  WHITE  SUBSTANCE  OF  THE  HUMAN 

SPINAL  CORD. 

The  dark  oval  bodies  are  cross-cut  axis  cylinders;  the  surrounding  light  halos 
represent  the  myelin  sheath.  The  coarser  trabeculae  are  connective  tissue,  contin- 
uous with  the  finer  neuroglia  framework.  (After  Salinger.) 

142 


NEUROGLIA 


143 


processes.  Two  varieties  of  these  cells  are  recognized:  the  spider  cell 
or  long-rayed  astrocyte,  with  a  small  cell  body  and  very  many  exception- 
ally long  and  slender  processes;  and  the  mossy  cells  or  short-rayed 


astrocytes,  whose  processes  are  shorter  and  somewhat  thicker  but  de- 
cidedly more  varicose  than  those  of  the  long-rayed  type. 

Recent  investigations  by  means  of  the  staining  methods  of  Weigert, 
Mallory,  and  Benda,  have  demonstrated  that  the  astrocytes.  as  seen  in 


144 


NEKVOUS  TISSUES 


the   Golgi  preparations,  probably  include  two   distinct  structures,  the 
glia  cells  and  the  glia  fibers. 

Glia  cells,  as  seen  in  sections  prepared  according  to  these  methods, 
appear  as  small  cells  with  large  and  deeply  staining  nuclei.  In  the 
small  glia  cells  the  cytoplasm  is  so  slight  as  to  form  scarcely  more  than 
a  mere  rim  about  the  nucleus;  in  the  larger  cells  the  cytoplasm  is  more 


FIG.  158. — A  LONG-RAYED  ASTROCYTE. 
Golgi's  stain.    Highly  magnified.     (After  Berkley.) 

abundant  and  the  processes  larger  and  more  numerous.  The  presence 
of  cytoplasmic  processes  gives  the  cell  an  irregularly  stellate  appearance. 
In  Golgi  preparations  these  processes  can 
not  be  distinguished  from  the  dense  net- 
work of  glia  fibers  with  which  they  are 
surrounded. 

The  Glia  Fibers.— The  glia.  fibers  com- 
prise numerous  filiform  fibrils  which  occur 
as  a  dense  network  around  the  glia  cells, 
from  which  they  radiate  in  all  directions. 
They  pass  alongside  of,  over,  or  under  the 
glia  cells;  their  filaments  have  even  been 
described  as  passing  entirely  through  the 
cytoplasm  of  the  cell.  Nevertheless  they 
appear  at  all  points  to  be  anatomically  dis- 
tinct from  the  cell  body. 

The  relation  of  the  glia  cells  to  the  fibers  of  neuroglia  is  perhaps 
comparable  to  the  arrangement  in  fibrous  or  reticular  tissue.    The  fibers 


FIG.     159. — A     SHORT-RAYED 
ASTROCYTE,  OR  MOSSY  CELL. 

Golgi's  stain.    Highly  mag- 
nified.   (After  Berkley.) 


NEUROGLIA  145 

of  each  of  these  tissues  appear  to  be  ontogenetically  derived  either  di- 
rectly or  indirectly  from  its  cells,  yet  when  fully  formed  they  often  exist 
as  anatomically  distinct  elements. 

Occurrence  of  Neuroglia. — Neuroglia  cells  and  fibers  occur  in  both 
gray  and  white  matter  of  the  central  nervous  system,  though  perhaps 
more  abundant  in  the  latter.  The  fibers  radiate  for  considerable  dis- 
tances from  their  glia  cells,  and  thus  form  a  supporting  tissue  for  the 
nerve  elements.  They  are  frequently  in  intimate  relation  with  the 
blood-vessels,  on  the  walls  of  which  many  of  the  glia  fibers,  particularly 


FIG.   160. — NEUROGLIA  CELL  WITH  ADJACENT  FIBERS  FROM  THE  PINEAL  BODY 
OF  A  YEARLING  SHEEP.     X  1500. 


the  thicker  or  mossy  variety,  terminate  in  expanded  plates,  which,  in 
some  parts,  form  an  almost  complete  outer  membranous  coat  of  the 
vessel. 

The  astrocytes  are  ontogenetic  derivatives  of  the  embryonic  epen- 
dyma  cells.  From  their  point  of  origin  around  the  neural  canal  they 
wander  to  all  portions  of  the  central  nervous  system,  and  even  into  the 
optic  and  olfactory  tracts,  which  are  embryonic  outgrowths  from  the 
fetal  cerebral  vesicles,  Thus  neuroglia  occurs  throughout  the  brain 


146 


NEEVOUS  TISSUES 


and  spinal  cord,  and  also  in  the  olfactory  nerves,  the  optic  chiasm,  and 
the  retina  of  the  adult. 

The  supporting  tissues  of  the  central  nervous  system  include,  besides 
the  neuroglia,  numerous  bands  or  trabeculae  of  fibrous  connective  tissue, 


FIG.  161. — NEUROGLIA  CELLS  AND  FIBERS  FROM  THE  SPINAL  CORD  OF  AN  ELEPHANT. 

The  letters  indicate  various  types  of  neuroglia  cells.    I,  a  leukocyte.    Benda's  stain. 
X  940.     (After  Hardesty.) 

which  push  inward  from  the  pia  mater,  carrying  with  them  the  vascular 
branches  for  the  supply  of  the  nervous  tissues,  and  which  penetrate 
deeply  into  the  substances  of  the  spinal  cord  and  brain. 


NERVE    TRUNKS 

Structure. — The  nerve  fibers  of  the  peripheral  nervous  system  are 
united  into  bundles  to  form  the  nerve  trunks  or  nerves.  Each  nerve 
is  surrounded  by  a  heavy  connective  tissue  sheath,  the  epineurium,  which 
sends  trabecula-like  septa  into  the  nerve.  These  septa  subdivide  the 
nerve  trunk  into  smaller  bundles  of  nerve  fibers,  the  funiculi.  The 
funiculus  forms  a  compact  bundle  of  nerve  fibers,  and  is  in  turn  invested 
with  a  sheath  of  dense  connective  tissue,  the  perineurium.  Hence  the 


NERVE  TRUNKS 


14? 


perineurium  stands  in  the  same  relation  to  the  funiculus  as  does  the 
epineurium  to  the  whole  nerve  trunk. 

Fro.ni  the  inner  surface  of  the  perineurium,  septa  pass  into  the 
funiculus  and  break  up  to  form  a  fine  connective  tissue  framework,  the 
endoneurium,  for  the  support  of  the  individual  nerve  fibers.  On  sepa- 
rating the  fibers  of  a  funiculus  with  needles  a  portion  of  this  fibrous 
endoneurium  remains  adherent  to  the  surface  of  the  nerve  fiber  and 
gives  the  appearance  of  an  outermost  fibrous  sheath,  the  so-called  con- 
nective tissue  sheath  of 
Henle.  * 

Nerve  trunks  fre- 
quently branch,  the 
branches  being  formed 
either  by  an  individual 
funiculus  or  by  groups  of 
funiculi.  In  the  smaller 
nerve  trunks  the  funiculi 
are  further  subdivided. 
It  is  by  anastomosis  of 
the  funiculi  that  most  of 
the  nerve  plexuses  are 
formed.  Individual  nerve 
fibers  of  the  medullated 
type  do  not  generally 
branch  except  in  those 
portions  which  are  naked 
axis  cylinders,  viz.,  at  the 

cytoproximal  portion  of  the  axon  by  means  of  collaterals,  and  at  the 
cytodistal  portion  by  means  of  end  arborizations.  Occasionally  also  col- 
laterals arise  at  a  node  of  Eanvier. 

Vascular  Supply. — The  nerve  trunks  are  well  supplied  with  blood- 
vessels. The  larger  of  these  are  found  in  the  epineurium,  and  from 
thorn  branches  of  considerable  size  enter  the  septa  to  be  distributed 
throughout  the  perineurium  to  the  funiculi.  The  coarser  septa  of  the 
endoneurium  contain  minute  arterioles  and  venules.  A  capillary  network 
with  elongated  meshes  occupies  the  finer  divisions  of  the  endoneurium, 
its  vessels  being  thus  brought  into  contact  with  the  nerve  fibers. 

Perivasr-ular  lymphatic  vessels  abound  in  the  epineurium  and  its 
septa,  and  lymphatic  tissue  spaces  are  found  throughout  the  connective 
tissue  of  the  nerve  trunk.  Where  the  cerebrospinal  nerve  trunks  pene- 


FIG.  162. — TRANSECTION  OF  THE  SCIATIC  NERVE 
OF  A  DOG. 

The  fat  cells  and  the  myelin  sheaths  of  the  nerve 
fibers  have  been  blackened  by  osmium  tetroxid.  a, 
fat  cells;  b,  b',  bloovi  vessels,  that  at  b'  lies  within  a 
funiculus;  c,  epineuiium;  d,  perineurium;  e,  coarser 
bands  of  the  endoneurium.  Osmium  tetroxid.  Photo. 
X  30. 


14S 


NERVOUS  TISSUES 


FIG.  163. — DIAGRAM  OF  THE  ORIGIN  AND  RELATIONS 
OF  THE  PERIPHERAL  MOTOR  AND  SENSORY  NEU- 
RONS. 

A  cylindrical  section  of  the  spinal  cord,  with  its 
ventral  and  dorsal  nerve  roots,  is  shown,  o,  nerve 
cell  of  the  ventral  horn  whose  axon  passes  through 
the  ventral  nerve  root,  b,  to  its  peripheral  termina- 
tion, c;  at  d  is  a  unipolar  sensory  nerve  cell  in  the 
dorsal  root  ganglion;  its  process  immediately  divides 
into  a  peripheral  and  a  central  branch.  The  central 
branch  enters  the  spinal  cord  and  at  e  divides  into 
an  ascending,  /,  and  a  descending,  g,  branch  from 
both  of  which  numerous  collaterals,  h,  enter  the  gray 
matter  and  terminate  in  fine  end  brushes.  The 
peripheral  branch  of  the  spinal  ganglion  cell  enters 
a  spinal  nerve  and  finds  its  way  to  its  termination 
which  is  here  represented  in  the  skin;  it  terminates 
partly  by  free  endings  among  the  epithelial  cells,  i, 
and  partly  in  connection  with  a  sensory  end  organ, 
fc,  in  this  case  a  tactile  corpuscle  of  Meissner.  (After 
von  Lenhosselc.) 


trate  the  meninges  these 
lymphatic  vessels  are  said 
to  be  continuous  with  the 
similar  vessels  of  the 
dura  mater. 

Minute  nerve  fiber 
bundles,  nervi  nervorum, 
are  also  found  in  the  epi- 
neurium;  their  fibers  are 
mostly,  if  not  entirely, 
distributed  to  the  blood- 
vessels. 


GANGLIA 

A  ganglion  may  be 
described  as  a  group  of 
nerve  cells  occurring  in 
the  course  of  a  peripheral 
nerve  trunk.  The  larg- 
est of  the  ganglia  form 
fusiform  swellings  in  the 
course  of  the  nerve,  which 
are  visible  to  the  naked 
eye.  The  smallest,  on 
the  other  hand,  contain 
not  more  than  half  a 
dozen  nerve  cells,  and 
these  must  be' sought  with 
the  aid  of  the  micro- 
scope and  can  only  be 
found  by  the  most  care- 
ful observation. 

Whatever  may  be  their 
size,  all  ganglia  appear 
to  have  a  similar  struc- 
ture, except  for  those 
differences  which  charac- 
terize the  sympathetic  as 


GANGLIA 


149 


distinguished  from  the  cerebrospinal  type.  The  essential  elements  of 
structure  are  the  nerve  cells,  nerve  fibers,  and  a  supporting  framework 
of  rather  dense  fibre-elastic  connective  tissue. 

Many  of  the  nerve  cells  of  the  adult  mammal  are  unipolar  in  the 
oerebrospinal  ganglia,  but  are  usually  multipolar  in  the  sympathetic. 
The  spinal  ganglia  of  the  lower  vertebrates  and  of  the  embryo  mammal, 


FIG.  164. — BIPOLAR 
CELL  FROM  A 
SPINAL  GAN- 
GLION OF  A  FISH. 

(Barker,    after 
Corti.) 


FIG.  165. — TRANSFORMATION  OF 
BIPOLAR  CELLS  INTO  UNIPOLAR 
CELLS  IN  THE  GASSERIAN  GAN- 
GLION OF  THE  PIG. 

(Barker,    after     van     Gehuch- 
ten.) 


however,  contain  bipolar  ganglion  cells.  In  mammals  the  two  processes 
of  the  embryonal  neuron  fuse  to  form  a  single  one  which  branches  in 
a  Y-  or  T-like  manner  soon  after  leaving  the  parent  cell  body. 

In  the  ganglia  of  the  acoustic  nerve  the  primitive  bipolar  condition 
of  the  neuron  is  retained;  and  the  cell  body  is  not  surrounded  by  a 
capsule. 

The  nerve  cells  of  all  other  ganglia  are  surrounded  by  a  capsule  of 
flat  epithelioid  cells  which  form  a  complete  investment  for  the  nerve 


150 


NERVOUS  TISSUES 


FIG.  166. — SECTION  THROUGH  THE  DORSAL 
ROOT  GANGLION  OF  THE  FIRST  THORACIC 
NERVE  OF  A  CAT. 

The  ganglion  cells  contain  a  large  vesicu- 
lar nucleus,  with  nucleolus,  and  are  en- 
veloped by  a  nucleated  capsule.  Several 
medullated  fibers  appear  among  the  gan- 
glion cells.  (From  Barker,  after  Hodge.) 

frequently  proximally  convoluted  and, 
after  branching  in  T-shape  fashion, 
passes  out  of  the  ganglion  to  become 
the  axis  cylinder  of  a  medullated  nerve 
fiber,  and  (2)  cells  with  a  slender  axon 
which  breaks  up  within  the  ganglion 
and  whose  terminal  arborizations  form 
a  pericapsular  plexus  around  the  cell 
capsule;  from  this  plexus  fine  end 
branches  penetrate  the  capsule  to  form 
a  pericellular  arborization  about  the 
nerve  cell  itself.  The  cells  of  this  lat- 
ter type  suggest  association  neurons 


cell  and  its  processes,  being  con- 
tinuous with  the  neurolemma. 
The  capsule  is  not,  however,  as 
a  rule,  closely  applied  to  the 
cell,  but  leaves  a  narrow  inter- 
val which  is  occupied  by  lymph 
or  'tissue  juice/ 

In  their  structure  the  gang- 
lion ic  neurons  do  not  appear  to 
differ  in  any  way  from  other 
neurons.  The  large  vesicular 
nucleus  with  its  distinct  nucleo- 
lus readily  distinguishes  these 
cells  from  those  of  neighboring 
tissues. 

The  studies  of  the  ganglion 
cells  by  Dogiel,  Eanvier,  and 
Cajal  have  done  much  to  ex- 
plain the  relations  of  these  cells 
to  each  other,  especially  in  the 
sympathetic  system,  where  they 
were  formerly  but  little  under- 
stood. In  the  spinal  ganglia 
Dogiel  (Anat.  Anz.,  1896)  de- 
scribed two  types  of  ganglion 
cells:  (1)  a  unipolar  cell  in 
which  the  axon  is  thick  and 


FIG.  167. — A  NERVE  CELL  FROM  A 
SECTION   OF   A   HUMAN   GAS- 
SERIAN  GANGLION. 
C,  capsule.    Nissl's  stain.    X  500. 


GANGLIA 


151 


within  the  ganglion.  Nerve  fibers  from  the  sympathetic  ganglia  also  enter 
the  spinal  ganglia  and  form  pericellular  arborizations  about  the  cells 
of  the  second  type.  Dogiel 
found  also  that  multipolar 
ganglion  cells  occur  in  the 
spinal  ganglia  of  the  adult  as 
vwell  as  of  the  embryo. 

The  more  recent  work  of 
Cajal  (1905),  Dogiel  (1908), 
and  Ranson  (1912)  has  re- 
vealed a  third  distinct  type 
of  cell  formerly  apparently 
included  under  Dogiel's  Type 
I :  smaller,  pyriform,  uni- 
polar cells  with  non-medul- 
lated  axon,  rarely  convoluted, 
dividing  into  a  central  and 
a  peripheral  branch,  the  ex- 
act terminations  of  which  are 
unknown ;  but  having  accord- 
ing to  Eanson  apparently  the 
same  distribution  as  the 
coarser  medullated  fibers  of 
Type  I,  and  probably  affer- 
ent in  nature  (Jour.  Comp. 
Neur.,  vol.  22,  1911).  In 
cat  and  rat  Hanson  esti- 
mates the  number  of  these 
cells  at  two-thirds  that  of  the 
total  number.  These  are  the 
cells  which  contribute  the 
bulk  of  the  very  numerous 
non-medullatcd  fibers  of  the 
spinal  nerves,  only  a  small 
portion  of  which  are  believed 


FIG.  168. — SCHEMATIC  REPRESENTATION  OF  THE 
RELATIONS  OF  THE  STRUCTURES  COMPOSING 
A  SPINAL  GANGLION. 


A  and  B,  ventral  and  dorsal  spinal  nerve 
roots;  C,  a  spinal  nerve;  D  and  E,  its  ventral 
and  dorsal  divisions;  F,  its  ramus  communicans. 
a,  nerve  cells  of  the  first  type,  whose  neuraxes 
divide  and  form  the  axis  cylinder  of  a  peripheral 
and  a  central  nerve  fiber;  6,  nerve  cells  of  the 
second  type,  whose  neuraxes,  n,  end  in  a  felt 
work  about  the  cells  of  the  first  type;  s,  sym- 
pathetic nerve  fibers  which  terminate  in  a  bas- 
ket work  about  the  cell  bodies  of  the  second 


1o  arise  in  sympathetic  gang-      type  of  ganglion  cells.    (After  Dogiel.) 
lia. 

With  the  exception  of  relatively  few  cells  of  bi-  and  multipolar  form, 
all  of  the  nerve  cells  of  the  spinal  ganglia  are  unipolar  in  the  adult 
condition.  In  the  case  of  the  larger  cells,  the  medullated  aeon  before 


152 


NERVOUS  TISSUES 


leaving  the  capsule  is  more  or  less  extensively  convoluted  over  the  cell 
body  forming  in  the  extreme  condition  a  so-called  'glomerulus.'  These 
same  cells  are  variously  modified  by  the  presence  of  short,  coarse  and 
fine  intra-  and  extracapsular  processes  (both  dendrons  and  collaterals) 
frequently  terminating  in  'end  disks'  (Huber).  Such  processes  may  fuse 
more  or  less  extensively  forming  the  'fenestrated'  variety  of  cells.  The 


y\\\\. 


FIG.  169. — COMMON  ATYPICAL,  THOUGH   PROBABLY  PERFECTLY  NORMAL,  NERVE 
CELLS  FROM  THE  SPINAL  GANGLION  OF  THE  DOG. 

o  and  b,  cells  with  collaterals  ending  in  'end  bulbs';  c,  a  multipolar  cell;  d  and  e, 
'fenestrated'  cells.     (Ranson,  Jour.  Comp.  Neur.,  22,  2,  1912.) 

axon,  prior  to  its  division,  may  split  at  one  or  several  points,  for  longer 
or  shorter  distances,  into  two  or  many  portions,  and  reunite  again  into  a 
single  fiber;  rarely  also  the  axon  may  have  two  or  more  points  of 
origin,  probably  the  result  of  fusions  of  collaterals  with  the  cell  body. 
These  more  complex  atypical  forms  are  said  to  predominate  in  man 
(Ranson,  Jour.  Comp.  Neur.,  24,  6,  1914).  Ranson  regards  them  to 
some  extent  at  least  as  transient  modifications,  which  may  return  to 
the  simpler  unipolar  condition.  Nageotte  (1907)  has  suggested  that 


THE  SYMPATHETIC  DIVISION  OF  THE  NEKVOUS  SYSTEM      153 

the  phenomena  of  end  disks  and  fenestratlons  signify  regenerative  activity. 
They  are  relatively  more  abundant  in  regenerating  transplanted  ganglia. 
But  they  are  abundant  also  in  pathological  ganglia  (Nageotte,  1906), 
and  in  fetal  ganglia  (Huber,  1913).  No  conclusive  evidence  has  yet  been 
presented  that  these  modified  forms  signify  functional  derangement. 


THE  SYMPATHETIC  DIVISION  OF  THE  NERVOUS  SYSTEM 

The  sympathetic  division  of  the  nervous  system  (autonomic  system) 
consists  essentially  of  three  sets  of  ganglia:  (1)  the  ganglionated  cords 
(sympathetic  trunks;  vertebral  ganglia);  (2)  the  prevertebral  plexuses; 
and  (3)  the  visceral  or  terminal  plexuses,  including  chiefly  the  my  enteric 
and  submucous  plexuses  of  the  alimentary  canal.  The  ganglia  of  the 
ganglionated  cords  are  segmentally  arranged,  and  interconnected  trans- 
versely (caudally)  and  longitudinally  by  plexuses  of  non-medullated  fibers. 
They  are  connected  also  with  the  spinal  nerves  by  the  white  and  gray  rami 
communicantes.  Homologous  ganglia  in  the  head  region,  less  definitely 
related  to  the  cerebral  nerves,  are  the  ciliary,  sphenopalatine,  submaxillary, 
subliugual,  parotid  and  otic  ganglia.  The  prevertebral  plexuses  develop 
from  non-segmentally  arranged  anlages  which  originate  as  outgrowths  at 
certain  levels  of  the  early  ganglionated  cord.  These  plexuses  contain  fewer 
and  smaller  cells,  with  a  preponderance  of  fibers,  e.g.,  cardiac,  celiac 
(semilunar;  solar),  hypogastric  and  pelvic  plexuses.  The'  myenteric  and 
submucous  plexuses  are  located  in  the  muscle  and  submucous  layers  re- 
spectively of  the  esophagus,  stomach  and  intestine.  Here  the  cells  are  still 
smaller  and  less  numerous  than  in  the  prevertebral  plexuses,  and  the  fiber- 
network  is  less  dense.  A  plexus  is  a  network  of  nerve  fibers  with  few  cells ; 
where  the  nerve  cells  are  relatively  abundant,  the  plexus  is  known  as  a 
ganglion.  The  embryonal  cells  (neuroblasts)  which  develop  into  sympa- 
thetic neurons  have  migrated  from  the  neural  crest,  possibly  in  part  also 
from  the  wall,  of  the  primitive  spinal  cord. 

Langley  employs  the  term  'autonomic  nervous  system'  for  all  that 
portion  of  the  peripheral  nervous  system  not  included  among  the  cerebro*- 
spinal  nerves,  commonly  designated  as  the  'sympathetic  system/  This 
comprises  four  components:  (1)  the  sympathetic  proper,  including  the 
autonomic  fibers  arising  from  the  thoracicolumbar  regions  of  the  spinal 
cord,  together  with  the  associated  vertebral  ganglia  and  their  postgang- 
lionic  neurons;  (2)  sacral  autonomic,  preganglionic  fibers  included  in  the 
roots  of  the  second,  third  and  fourth  sacral  nerves,  together  with  the  asso- 
ciated postganglionic  neurons;  (3)  cranial  autonomic,  a  group  of  fibers 
arising  from  the  midbrain  and  the  medulla  (this  component  is  separated 
from  the  sympathetic  proper  by  the  whole  extent  of  the  cervical  region 


154 


NERVOUS  TISSUES 


of  the  spinal  cord,  which  region  lacks  white  rami  communicantes) ;  (4) 
enteric,  including  the  myenteric  and  submucous  plexuses  of  the  digestive 
tube.  Langley  proposes  also  the  term  'parasympathetic'  to  designate  the 
sacral  and  cranial  autonomic  fibers,  since  in  many  parts  of  the  body  they 
overlap  the  distribution  of  the  sympathetic  proper. 

In  the  sympathetic  (or  autonomic)  ganglia  Dogiel  ( Anat.  Anz.,  1896) 
likewise  recognized  two  cell  types,  in  general  smaller  than  those  of  the 


170. — SYMPATHETIC  NEURONS. 


A,  in  myenteric  plexus,  ileum  of  cat;  B  and  C,  in  myenteric  plexus,  ileum  of  dog; 
D,  E,  F,  in  submucous  plexus,  ileum  of  dog;  o,  axon.  A  corresponds  to  Dogiel's 
Type  I,  a  motor  neuron;  B  and  C  correspond  to  Dogiel's  Type  II,  probably  sensory 
neurons.  (After  Kuntz,  Jour.  Comp.  Neur.,  23,  3,  1913.) 

spinal  ganglia:  (1)  small  multipolar  fusiform  or  stellate  nerve  cells  with 
5  to  20  dendrons  and  an  axon  which  enters  the  nerve  trunks  as  a  non- 
medullated  fiber,  but  may  later  acquire  a  thin  medullary  sheath — motor 
neurons;  (2)  larger  spheroidal  nerve  cells  with  1  to  16  dendrons  and  a 


THE  SYMPATHETIC  DIVISION  OF  THE  NERVOUS  SYSTEM      155 

single  axon  which  also  enters  the  nerve  trunk  as  a  non-medullated  nerve 
fiber,  but  may  later  acquire  a  very  thin  medullary  sheath,  perhaps  sen- 
sory neurons.  The  dendrons  of  the  second  type  are  distinguished  from 
those  of  the  first  by  being  very  long  and  slender  and  also  by  entering 
the  nerve  trunks,  to  pass,  presumably,  to  neighboring  ganglia.  The 
dendrons  of  the  first  cell  type  on  the  other  hand,  are  shorter,  thicker, 
and  end  in  relation  with  other  cells  within  the  same  ganglion.  Carpen- 
ter and  Conel  report  also  intermediate  types  in  the  cat. 

In  certain  rodents  (rabbit  and  guinea  pig)  many  of  the  neurons  of 
the  vertebral  and  pre vertebral  autonomic  ganglia  are  bi-nucleate  (Car- 
penter and  Conel,  Jour.  Comp.  Neur.,  24,  3,  1914). 

The  ganglionic  cell  group  is  excentrically  placed  as  regards  the  axis 
of  the  nerve  trunk,  some  funiculi  apparently  passing  the  ganglion  with- 
out being  in  any  way  connected  with  its  nerve  cells. 

The  sympathetic  differ  from  the  cerebrospinal  ganglia  chiefly  in  the 
relative  preponderance  of  non-medullated  nerve  fibers  in  the  former  and 
of  the  medullated  type  in  the  latter.  Just  as  the  cerebrospinal  ganglia 
receive  a  few  non-medullated  sympathetic  fibers,  so  also  the  sympathetic 
ganglia  receive,  through  the  medium  of  the  white  rami  communicant es, 
a  certain  number  of  medullated  nerve  fibers  from  the  cerebrospinal  sys- 
tem. Moreover,  with  the  intense  staining  method  of  Weigert,  very  thin 
medullary  sheaths  may  now  be  demonstrated  where  formerly  they  were 
not  suspected. 

The  sensory  and  motor  neurons  of  the  cerebrospinal  division  show 
characteristic  differences  in  their  chromophilic  substance.  In  the  cere- 
bral and  spinal  ganglia  the  cell  bodies  of  the  sensory  neurons  contain 
fine  Nissl  granules  evenly  distributed  throughout  the  cytoplasm.  The 
motor  cell  bodies  from  the  spinal  cord  contain  fewer  and  much  larger 
chromophilic  flakes.  The  sympathetic  neurons  likewise  present  a  charac- 
teristic and  constant  appearance:  the  chromophilic  granules  are  inter- 
mediate in  size  and  generally  massed  toward  the  periphery  (Malone; 
Carpenter  and  Conel). 

The  ganglia  are  supplied  with  blood  vessels  and  lymphatic  vessels 
in  a  manner  similar  to  the  nerve  trunks  in  whose  course  they  occur. 

The  earlier  conception  of  the  nervous  system  interpreted  the  nerve 
fiber  (axon)  as  the  fusion  product  of  a  chain  of  cells  extending  from  its 
proximal  to  its  distal  end.  The  axis  cylinder  fibrils  were  regarded  as 
differentiation  products  of  the  cytoplasm  (Schwann;  Apathy;  et  al.).  The 
view  which  now  prevails  interprets  the  axon  as  the  outgrowth  of  the  cell 
body  to  which  it  is  attached  (His;  Cajal;  et  aL).  The  tissue  culture 


156 


NERVOUS  TISSUES 


FIG.    171.— THE 

SPROUTING  OF  AN 
AXON  BY  A  NEU- 
KOBLAST  FROM 
THE  SPINAL 
CORD  OF  A  FROG 
EMBRYO. 


From  a  live  spec- 
imen grown  in 
lymph;  the  cell 
body  is  filled  with 
yolk  granules;  the 
protoplasmic  proc- 
ess (axon)  is  of 
hyaline  appearance 
and  undergoes  ame- 
b  o  i  d  movements. 
(Harrison.) 


work  of  Harrison  and  others  has  established  the  out- 
growth view  upon  a  firm  basis  of  observational  data. 
By  growing  small  pieces  of  the  embryonic  spinal  cord 
of  frogs  in  lymph,  Harrison  could  observe  the  cells 
sprouting  an  axon  process  (Figs.  171  and  172).  He 
describes  the  beginning  of  a  nerve  fiber  as  an  outflow 
of  hyaline  protoplasm  from  cells  which  were  situated 
within  the  central  nervous  system.  The  experiments  of 
Harrison  upon  frog  larvae  demonstrate  further  that  the 
sheath  cells  of  the  neurolemma  of  motor  and  sensory 
fibers  have  their  origin  in  the  ganglionic  crest,  there- 
fore ectodermal,  arid  that  they  are  unessential  to  the 
formation  of  the  fibrils  of  the  axis  cylinder.  He  ex- 
cised the  dorsal  half  of  the  cord,  including  the  neural 
crest,  and  observed  that  in  such  larvae  the  fibers  of  the 
motor  roots  did  not  acquire  sheath  cells.  On  the  con- 
trary, when  he  excised  the  ventral  half  of  the  cord, 
dorsal  root  fibers  developed  normally  with  a  neuro- 
lemma, but  the  sheath  cells  which  migrated  to  the  lo- 
cation where  the  ventral  fibers  normally  appear  were 
unable  to  produce 


these  fibers  in  the 
absence  of  neuro- 
blasts  in  the  ven- 
tral half  of  the 
cord.  (Anat.Rec., 
2,  9,  1908.) 

The  influence 
which  guides  the 
nerve  along  its 

proper  path  is  apparently  exerted  by 
the  tissue  which  is  to  be  innervated. 
The  essential  factors  comprising  this 
influence  are  obscure;  they  may  be  of 
a  chemotropic  nature.  It  must  be 
emphasized,  however,  that  the  con- 
nection between  a  particular  nerve 
and  its  tissue  terminal  is  made  rela- 
tively early,  that  is,  while  the  two 
elements  are  still  spatially  relatively 
closely  associated.  Probably  mechan- 
ical stimuli,  inducing  thigmotropic 
reactions,  also  play  an  important  role 
in  determining  the  path  of  a  nerve 


FIG.  172. — THE  SPROUTING  OF  AN 
AXON  BY  A  NEUROBLAST  FROM  THE 
SPINAL  CORD  OF  A  FROG  EMBRYO. 

Two  views  of  the  same  nerve  fiber, 
grown  in  lymph,  taken  twenty-five 
minutes  apart.  (Harrison.) 


NEURONE  THEORY'  157 

fiber.  The  earlier  relations  are  of  course  modified  during  growth;  the 
definitive  relation  between  nerve  and  end-organ  are  acquired  by  mutual 
adjustment.  Recently  Harrison  has  contributed  further  experimental  evi- 
dence in  support  of  the  view  that  the  growing  axoii  is  guided  through  a 
stereotropic  response  (Jour.  Exp.  Zool.,  17,  4,  1914). 

By  cultivating  sympathetic  neurons  from  pieces  of  the  intestine  of  the 
embryo  chick  in  saline  solutions,  W.  H.  and  Margaret  R.  Lewis  (Anat.  Rec., 
6,  1,  1912)  have  been  able  to  demonstrate  that  here  also  the  fibers  arise  as 
outgrowths  of  nerve  cells. 


NEURONE  THEORY 

The  work  of  Harrison,  the  Lewises  and  many  others,  including  both 
experimental  and  morphological  investigations,  leave  scarcely  any  fur- 
ther doubt  of  the  accuracy  of  the  Neurone  Theory  of  Waldeyer  (1891), 
which  simply  applies  the  Cell  Theory  of  Schleiden  and  Schwann  (1838- 
39)  to  the  nervous  system.  It  holds  that  the  unit  of  structure  is  the 
neuron  (neurocyte),  consisting  of  cell-body  (cyton)  and  processes,  in- 
cluding one  axon,  and  one  or  several  dendrons.  The  nervous  system 
c6nsists  therefore  of  innumerable  associated  neurons.  Neurons  arise 
each  from  a  single  embryonic  cell,  the  neuroblast,  retain  their  independ- 
ence throughout  life,  and  make  connection  with  each  other  in  general 
only  by  contact,  which,  however,  is  sufficiently  intimate  to  insure  func- 
tional continuity.  A  neuron  exhibits  a  structural  and  functional  po- 
larity; and  constitutes  a  trophic  unit  for  the  maintenance  of  whose 
metabolic  activity  a  nucleus  is  necessary. 

Further  confirmation  of  the  outgrowth  interpretation  as  opposed  to 
that  of  autogenesis  of  the  axon  has  recently  been  furnished  by  the  experi- 
ments of  Clark  (Jour.  Comp.  Nexir.,  24,  1,  1914)  on  the  domestic  fowl. 
By  prolonged  exclusive  feeding  of  polished  rice  he  induced  degeneration 
in  the  peripheral  medullated  nerves.  On  return  to  an  adequately  nutritive 
diet  regeneration,  accompanied  by  a  return  to  normal  locomotion  and  func- 
tion, followed.  The  material  thus  gave  opportunity  for  a  microscopic  study 
of  the  steps  in  the  nerve  degeneration  and  regeneration.  When  the  degen- 
erative process  had  not  been  excessively  prolonged  a  new  axis  cylinder  grew 
down  the  old  medullary  sheath,  which  returned  to  normal;  when  greatly 
prolonged  the  myelin  disappeared  and  the  nuclei  of  the  neurolemma  multi- 
plied, giving  an  appearance  very  similar  to  that  of  embryonic  nerve  fibers 
('bandfaseni'  stage).  Clark  concludes  that  the  function  of  these  excessive 
sheath  cells  is  the  removal  of  the  degenerating  myelin,  a  new  medullary 


158  '  NERVOUS  TISSUES 

sheath  being  supplied  probably  by  joint  influence  of  the  new  axis  cylinder 
and  the  neurolemma  cells. 

Mitochondria  of  granular  and  rod  forms  are  abundant  in  the  neuro- 
blasts.  Meves,  Duesberg  and  others  have  claimed  that  these  differentiate 
into  neurofibrils.  The  recent  work  of  Cowdry  (Amer.  Jour.  Anat.,  15,  4, 
1914)  on  chick  embryos  proves  the  untenability  of  this  view.  Cowdry 
shows  that  the  neurofibrils  arise  as  a  differentiation  of  the  ground  substance 
of  the  neuroblast ;  and  that  mitochondria  persist  in  undiminished  numbers 
throughout  the  period  of  neurofibril-development.  Moreover,  it  is  now 
known  that  mitochondria  are  present  also  in  adult  neurons.  They  are  ap- 
parently fundamental  cytoplasmic  constituents  of  a  metabolically  active 
cell. 

Spinal  ganglion  cells  of  certain  adult  mammals  (cat  and  rabbit)  have 
been  kept  alive  in  tissue  cultures  for  as  long  as  twenty  days  (Minea,  Anat. 
Anz.,  46,  20,  1914).  The  cells  remain  apparently  normal,  augment  their 
amount  of  chromophilic  substance,  produce  new  neurofibrils,  develop  short 
processes  with  end-plates  (neuropodia)  and  become  fenestrated,  but  do  not 
proliferate. 


CHAPTER   VI 
PERIPHERAL  NERVE  TERMINATIONS:  END  ORGANS 

All  peripheral  nerve  fibers  end  either  as  terminal  fibrils  or  in  rela- 
tion to  a  highly  specialized  end  organ.  The  function  of  these  latter 
bodies  is  apparently  included  in  the  changing  of  ordinary  stimuli- — 
mechanical,  thermal,  chemical,  etc. — into  a  nerve  impulse,  or,  vice  versa, 
the  changing  of  a  nerve  impulse  to  a  cell  stimulus  which  results  in 
motion,  secretion,  etc.,  according  to  the  nature  of  the  tissue  cells  which 
are  thus  stimulated.  Some  of  the  nerve  end  organs  are  connected  with 
efferent  (motor)  fibers,  others  with  afferent  (sensory)  fibers.  Nerve 
endings  are  found  in  nearly  all  the  tissues  of  the  body  with  the  exception 
of  cartilage  and  the  calcareous  tissue  of  the  bones. 

NERVE   ENDINGS   IN   EPITHELIUM 

Intra-epithelial  nerve  fibrils  are  derived  from  the  nerve  fiber  plexuses 
in  the  subjacent  connective  tissue ;  the  epithelium  usually  receives  a  very 
abundant  nerve  supply.  The  following  types  of  intra-epithelial  nerve 
endings  have  to  be  considered. 

1.  End  Fibrils. — This  form  of  nerve  termination  has  been  demon- 
strated in  all  the  varieties  of  epithelium.     Terminal  nerve  fibers  enter 
the  epithelial  tissue  as  naked  fibrils,  often  somewhat  varicose,  which  form 
a  delicate  plexus  between  the  epithelial  cells.    The  terminal  fibrils  of  this 
plexus  frequently  end  in  minute  knoblike  enlargements  which  are  in 
contact  with  the  surface,  but  rarely,  if  ever,  penetrafe  the  interior  of  the 
epithelial  cells.     The  'trefoil  plates'  of  Bethe  represent  unusually  large 
end  knobs. 

2.  Tactile  Cells  (Mcrkel). — These   are   modified   epithelial   cells, 
with  clear  cytoplasm  and  a  slightly  vesicular  nucleus,  which  are  found 
in  the  deeper  layers  of  the  stratified  epithelium  of  the  epidermis  and 
in  the  root  sheaths  of  hairs.    These  cells  are  recognized  by  their  vesicu.- 

159 


160 


PERIPHERAL  NERVE  TERMINATIONS:   END  ORGANS 


FIG. 


173. — NERVE  ENDINGS  IN  THE 
THELIUM  OF  THE  LARYNX. 


On  the  left  a  taste  bud;  on  the  right,  nerve 
endings  in  the  stratified  epithelium  are  rep- 
resented. (After  Retzius.) 


lar  character  and  by  the  fact  that  they  occur  most  abundantly  in  the 

intcrpapillary  portions  of  the  epidermis.     The  deeper  surface  of  the 

tactile  cell  rests  in  a  cuplike  ex- 
pansion of  a  terminal  nerve 
fibril  which  is  known  as  the  tac- 
tile meniscus. 

3.  Neuro-epithelium.— The 
cells  of  some  types  of  neuro- 
epithelium,  e.g.,  the  olfactory 
cells,  are  true  nerve  cells ;  others 
are  modified  epithelial  cells,  in 
relation  to  which  the  nerves  ter- 
minate by  intercellular  end  fi- 
brils. The  neuro-epithelium  of 
the  eye  and  the  ear  will  be  de- 
scribed in  the  chapters  devoted  to  these  organs,  that  of  the  gustatory 

organ  forms  typical  nerve  end  organs,  the  taste  buds. 

TASTE  BUDS   (Gustatory  Organ}. — These  end  organs  appear  to  be 

concerned  with  the  special  sense  of  taste.     They  occur  in  the  stratified 

epithelium  of  the  base  of  the 

tongue,    uvula,    soft    palate, 

and  epiglottis.    Disse  has  also 

found   similar    structures   in 

the  nasal  mucous  membrane. 

They  are  most  abundant  on 

the  lateral  surfaces  of  the  cir- 

cumvallate    papillae    of    the 

tongue  and  on  the  walls  of 

the  sulci  in  the  foliate  pa- 
pillae which  are  most  highly 

developed  in  the  rabbit.  They 

are  occasionally  found  on  the 


FIG.  174.  —  TACTILE  CELLS  IN  THE  EPITHELIUM 
OF  THE  GROIN  OF  A  GUINEA-PIG. 


a,  tactile  cell;  c,  epithelial  cell;  m,  tactile  men- 
iscus, at  the  end  of  a  nerve  fibril;  n,  nerve  fiber. 
Chlorid  of  gold.  Highly  magnified.  (After 
Ranvier.) 


fungiform  papillae  of  the 
tongue,  where  they  occur  in 
considerable  numbers  in  fetal 
life  but  mostly  disappear  be- 
fore birth,  and  in  the  lateral  walls  of  the  sulci  about  the  circumvallate 
papillae. 

Taste  buds  are  ovoid,  ellipsoidal,  or  spheroidal  masses  which  occupy 
almost  the  entire  depth  of  the  epithelial  layer.     Their  broad  base  rests 


NERVE  ENDINGS  IN  EPITHELIUM 


161 


Supporting  ceil. 


Neuro-epit  helial 
cell. 


-Rod  cell. 


upon  the  basement  membrane,  their  narrower  apex  extends  nearly  to 
the  surface  of  the  epithelium.  The  apex  of  the  bud  is  thus  covered  by 
the  superficial  squamous  epithelial  cells  except  for  a  narrow  tubular 
opening  which  overlies  the  superficial  pole  of  the  end  organ.  This 
canal  presents  an  external  and  an  internal  ostium,  respectively  desig- 
nated the  outer  and  inner  taste  pore.  The  inner  taste  pore  leads  into  a 
goblet-shaped  depression  in  the  apex  of  the  taste  bud,  into  which  the 
cuticular  processes  of  the  gustatory  cells  project.  Composite  buds  with 
two  and  three  pores  are  g^. 

common  in  the  foliate 
papilla  of  the  rabbit; 
Heidenhain  (Anat. 

Anz.,  45,  16,  1914)  re- 
ports also  buds  with 
four,  five  and  six  pores. 

The  taste  buds  con- 
sist essentially  of  two 
varieties  of  cells,  the 
gustatory  and  the  sus- 
tentacular.  The  latter 
include  the  broad  outer 
sustentacular  or  teg- 
mental  cells  at  the  sur- 
face of  the  bud,  the  in- 
ner sustentacular  cells 
within,  and  the  basal 
cells  which  lie  near  the 
basement  membrane. 

The  Gustatory  Cells. — The  gustatory  cells  are  slender  neuro-epithe- 
lial  structures  whose  nucleus  causes  a  fusiform  enlargement  near  their 
center  or  toward  the  basal  end.  Their  cytoplasm  is  finely  granular; 
their  nucleus  stains  deeply  and  is  ovoid  or  rod-shaped.  The  distal  end 
of  the  cell  carries  a  delicate,  highly  refractive  cuticular  process  which 
projects  beyond  the  apices  of  the  sustentacular  cells  and  as  far  as  the 
inner  taste  pore.  Their  proximal  end  is  often  bifid,  forked,  or  so  flat- 
tened as  to  form  a  footlike  'extremity  which  is  connected  with  the  basal 
cells  by  fine  processes.  Sapid  substances  in  solution  enter  the  pore  and 
stimulate  the  taste  cells  through  the  hair  processes. 

Sustentacular  Cells. — The  outer  and  inner  sustentacular  cells  are 
elongated  epithelioid  cells,  having  an  ovoid  or  spheroidal  vesicular 


fibrils. 


FIG.  175. — SCHEMATIC  REPRESENTATION  OP  A  TASTE 
BUD. 

(After  Hermann,  from  Bohm  and  von  Davidoff .) 


162 


PERIPHERAL  NERVE  TERMINATIONS:  END  ORGANS 


nucleus  which  causes  no  bulging  of  the  protoplasm,  and  a  coarsely  retic- 
ular  and  frequently  vacuolated  cytoplasm.  The  distal  ends  of  the 
cells  taper  to  blunt  points  which  collectively  form  the  lateral  wall  of 
a  goblet-shaped  cavity  at  the  apex  of  the  taste  bud.  The  proximal  end 


FIG.  176. — TASTE  BUD  FROM  THE  HUMAN  TONGUE. 

A,  in  longitudinal  section;  B,  transection  through  the  deeper  third;  C,  transection 
through  the  base.  Bz,  basal  cells;  Ez,  extra-bulbar  cells;  Gz,  gustatory  cell;  L,  leuko- 
cytes, in  A  one  of  these  is  seen  in  the  pore;  Pg,  perigemmal  space;  Sg,  subgemmal 
spaces;  Sp,  connective  tissue  of  the  tunica  propria;  Sz,  sustentacular  cells;  x,  cells  of 
the  adjacent  epithelium.  (After  Graberg.) 

is  broad,  often  blunt  or  serrated,  and,  like  the  gustatory  cells,  it  is  con- 
nected with  the  basal  cells  by  protoplasmic  processes. 

The  Basal  Cells.— The  basal  cells  are  flattened  bodies  with  small 
ovoid  vesicular  nuclei  and  a  relatively  small  amount  of  cytoplasm  which 
is  prolonged  into  numerous  processes  that  appear  to  be  continuous  with 
the  sustentacular  and  gustatory  cells.  These  cells  have  been  considered 
as  having  a  similar  function  to  the  sustentacular  cells. 


NERVE  ENDINGS  IN  CONNECTIVE  TISSUE 


163 


The  Fibers. — The  nerve  fibrils  of  the  taste  buds  are  derived  from  a 
sub-epithelial  plexus  which  distributes  terminal  fibrils  to  the  gustatory 
and  sustentacular  cells, — intragemmal  fibers, — and  to  the  intervening 
portions  of  the  stratified  epithelium, — intergemmal  fibers, — where  they 
terminate  in  end  fibrils.  Von  Lenhossek  (Anat.  Anz.,  1892)  states  that 
the  intragemmal  and  intergemmal  fibers  are  never  derived  from  the  same 
nerve  fiber.  Circumgemmal  fibers,  distributed  as  varicose  fibrils  to  the 
surface  of  the  taste  bud,  may,  however,  arise  from  the  same  nerve  fiber 
as  the  intragemmal  branches. 

Those  nerve  fibers  which  enter  the  taste  buds  form  fine  varicose  fibrils 
which  are  closely  applied  to,  but  are  not  continuous  with,  the  gustatory 
and  the  sustentacular  cells.  The  terminal  twigs  of  these  fibrils  end  by 
minute  end  knobs  which  are  scarcely  distinguishable  from  the  varicosities 
(Fig.  175). 


NERVE   ENDINGS   IN   CONNECTIVE   TISSUE 

The  nerve  fibers  form  extensive  plexuses  in  the  connective  tissues 
from  which  terminal  branches  are  distributed  to  the  epithelium  (free 
sensory  endings),  the  walls  of  the  blood  and 
lymphatic  vessels  (sympathetic  vasomotor 
endings),  and  to  the  numerous  sensory  end 
organs  (encapsulated  endings)  which  occur 
in  abundance  in  most  of  the  connective  tis- 
sues. Nerves  also  terminate  in  connective 
tissue  by  free  end  fibrils  some  of  which,  as 
in  the  epithelial  tissues,  possess  minute  end 
knobs.  Free  nerve  endings  of  this  nature 
occur  in  the  tendons,  the  lungs,  the  stom- 
achal and  intestinal  mucous  membranes, 
the  meninges,  and  in  the  superficial  layer 
of  the  corium  of  the  skin  and  the  hair 
follicles. 

The  following  types  of  nerve  end  organs 
are  found  in  connective  tissue: 

1.     Tactile  Corpuscles     (Touch    Cor- 
puscles  of   Meisxner). — These   organs   are 
formed   by   the   terminal   expansion  of   a 
nerve  fiber,  which  forms  a  varicose  plexus  inclosed  within  a  delicate  con- 
pectiye  tissue  sheath.    The  nerve  fiber,  or  its  primary  branches,  prior  to 


FIG.  177. — TACTILE  CORPUSCLE 
OF  MEISSNER  FROM  THE  SKIN 
OF  THE  HUMAN  TOE. 
Bl,  blood-vessel;  N,  medul- 

lated     nerve     fiber.      Highly 

magnified.      (After     Schieffer- 

decker.) 


164 


PEEIPHEEAL  NERVE  TERMINATIONS:   END  ORGANS 


its  ultimate  division  makes  several  spiral  turns  about  the  corpuscle.  The 
course  of  the  nerve  fiber  gives  the  corpuscle  a  peculiar  spirally  striated 
appearance.  Within  the  corpuscle  the  nerve  fiber  breaks  into  a  plexus 
of  varicose  fibrils,  many  of  which  end  in  knobbed  extremities.  The  cor- 


FIG.    178. — TACTILE    CORPUSCLE    OP 
MEISSNER. 

b,  epithelioid  cells;  c,  nerve  endings; 
e,  connective  tissue  capsule.  (Maxi- 
mow,  after  Van  de  Velde.) 


FIG.  179. — TACTILE  CORPUSCLE  OP 
MEISSNER. 

a,  nerve  fibrils  which  enter  the  corpuscle 
and  supply  its  nerve  skein.  Methylene 
blue.  Very  highly  magnified.  (After 
Dogiel.) 


puscles  also  contain  many  flattened  or  cuneiform  epithelioid  cells  which 
are  interspersed  among  the  nerve  fibrils. 

Tactile  corpuscles  occur  in  largest  numbers  in  the  cutaneous  papillce 
of  the  finger  tips,  where  there  may  be  as  many  as  twenty  to  the  square 
millimeter.  They  are  found  in  considerable  abundance  also  in  other 
highly  sensitive  regions,  including  especially  the  corium  of  the  toe  tips, 
the  lips,  nipple,  conjunctiva,  glans  penis  and  clitoris.  The  cutaneous 
senses  comprehend  four  different  qualities  of  sensation :  pressure,  warmth, 
cold  and  pain.  These  are  mediated  by  two  distinct  groups  of  sensory 
fibers  ending  in  the  skin:  the  one  conveys  the  impulses  for  pain  and 
extremes  of  temperature  (protopathic  sensibility),  the  other  for  light 
pressure  and  small  changes  of  temperature,  (epicritic  sensibility).  The 


NERVE  E.VDTNGS  IN  CONNECTIVE  TISSUE 


165 


FIG.  180.— RUFFINI'S  END 
ORGAN. 

A  single  nerve  fiber  breaks 
up  to  form  the  tangle  of  nerve 
fibrils  within  the  organ,  gll, 
medullary  sheath;  il,  terminal 
fibrils  of  the  axis  cylinder;  L, 
connective  tissue  capsule.  (Af- 
ter Ruffini.) 

ally  at  its  end.     X/o\\-  and 
tributed  to  several  of  1  IK-SI- 


various  subcutaneous  endings  mediate  sub- 
cutaneous sensibility  to  pressure  and  move- 
ment. 

2.  Ruffini 's  End  Organs.— These 
bodies,  also  known  as  terminal  cylinders, 
resemble  the  tactile  corpuscles  in  structure 
but  possess  a  definite,  though  thin,  connec- 
tive tissue  sheath  within  which  the  ter- 
minal arborization  of  the  nerve  fiber  is 
embedded  in  a  granular  core.  They  occur 


FIG.  181. — END  BULB  OF  KRATJSE  FROM  THE  MAR- 
GIN OF  THE  OCULAR  CONJUNCTIVA. 

The  axon  forms  a  dense  skein  within  the  en- 
capsulated bulb.  Methylene  blue.  Highly  mag- 
nified. (After  Dogiel.) 


in  the  deeper  part  of  the  true  skin  near  its 
junction  with  the  subcutaneous  tissue  and 
in  the  connective  tissue  septa  of  the  latter, 
whereas  the  tactile  corpuscles  are  found  in 
the  papillary  layer  of  the  skin.  Ruffini 
(Arch.  ital.  de  biol.,  1894)  states  that  they 
occur  in  large  numbers  in  the  skin  of  the 
finger  tips,  where  they  rival  in  number  the 
rather  more  deeply  placed  Pacinian  cor- 
puscles. 

The  Ruffini  organs  are  cylindrical  in 
shape  and  their  nerve  fibers  usually  enter 
at  the  side  of  the  organ,  though  occasion- 
then  a  single  branching  nerve  fiber  is  dis- 
end  organs. 


166 


PERIPHEEAL  NEEVE  TERMINATIONS :  END  OEGANS 


3.  End  Bulbs  (Krause). — These  structures  (bulbous  corpuscles}, 
together  with  those  which  follow,  form  the  true  so-called  encapsulated 
nerve  end  organs.  In  the  end  bulbs  the  nerve  forms  a  terminal  arboriza- 


FIG.  182. — GENITAL  CORPUSCLES  FROM  THE  CLITORIS  OF  A  RABBIT. 


A  single  axon  from  the  nerve  plexus  enters  each  corpuscle. 
Highly  magnified.      (After  Retzius.) 


Methylene  blue. 


tion  of  the  varicose  and  knobbed  fibrils  which  freely  anastomose  (Dogiel, 
Kuffini).  The  bulb  is  invested  with  a  distinct  connective  tissue  capsule. 
On  entering  the  bulb  the  nerve  fiber  loses  its  sheaths  and  the  perineu- 
rium,  now  represented  by  Henle's  sheath,  becomes  continuous  with  the 


FIG.  183. — A  LAMELLAR  CORPUSCLE  FROM  THE  MESENTERY  OF  A  CAT. 
A,  a  nearly  axial  section;  B,  a  transection.    Hematein  and  orange  G.     X  410. 


capsule  of  the  bulb.     Within  the  capsule  the  nerve  fibrils  are  embedded 
in  a  granular  inner  bulb. 

The  end  bulbs  vary  much  in  both  size  and  shape.  They  may  be 
either  spheroidal,  ovoid,  twisted  or  convoluted,  branched  or  compound,  or 
cylindroid.  They  are  abundantly  found  in  the  conjunctiva,  but  also 


NERVE  ENDINGS  IN  CONNECTIVE  TISSUE 


167 


occur  in  the  corium  of  the  skin.  Similar,  though  more  highly  developed, 
end  Imlbs  form  the  so-called  genital  corpuscles  which  are  found  in  con- 
siderable numbers  in  the  connective  tissue  of  the  glans  penis,  prepuce, 
and  clitoris.  In  some  of  the  smaller  (cylindrical)  end  bulbs  found  in 
the  tendons,  the  mucous  membranes,  and  in  certain  portions  of  the  skin, 


FIG.  184. — A  LAMELLAR  CORPUSCLE  FROM 
THE  PLEURA  OF  A  CHILD. 

a,  lamellae;  b,  nerve  fiber;  c,  nerve. 
Methylene  blue.  Moderately  magnified. 
(After  Dogiel.) 


FIG.  185. — LAMELLAR  CORPUSCLE  FROM 
THE  MESENTERY  OF  A  KITTEN. 

The  nerve  fiber  shows  lateral  proc- 
esses, many  of  which  are  knobbed. 
Methylene  blue.  Moderately  magni- 
fied. (After  Sala.) 


the  nerve  fiber  fails  to  divide  but  ends  near  the  distal  extremity  of  the 
bulb  in  a  small  fusiform  end  knob. 

4.  Lamellar  Corpuscles  (PaciniaM  Corpuscles,  Voter's  Corpuscles, 
Vater-Pacinian  Corpuscles). — These  are  among  the  largest  of  the  nerve 
end  organs.  In  the  mesentery  of  the  cat  they  are  of  macroscopic  size, 
varying  in  length  from  two  to  three  millimeters.  They  assume  the  form 
of  a  large  ovoid  thickening,  placed  upon  the  end  of  a  nerve  fiber.  The 
12 


168 


PEEIPHERAL  NERVE  TERMINATIONS:   END  ORGANS 


Pacinian  corpuscle  consists  of  a  thick  lamellated  connective  tissue  coat, 
and  a  central  granular  protoplasmic  core  which  is  pierced  by  the  nerve 
fiber.  The  medullated  nerve  fiber  enters  the  axis  of  the  corpuscle,  its 
Henle's  sheath  becoming  continuous  with  the  superficial  capsule  of  con- 


FIG.  186. — A  LAMELLAR  CORPUSCLE  IN 
LONGITUDINAL  SECTION,  SHOWING 
A  NETWORK  OF  SPIRAL  ELASTIC 
FIBERS. 

Weigert's  elastic  tissue  stain.     Highly 
magnified.     (After  Sala.) 


FIG.  187. — AXIAL  SECTION  OF  A  COR- 
PUSCLE OF  HERBST  FROM  A  DUCK'S 
TONGUE. 

a,  medullated  nerve  fiber;  b,  naked 
axial  nerve  fiber  with  a  bulbous  end;  c, 
nuclei  of  the  core;  d,  inner  concentric 
capsule;  e,  nuclei  of  the  outer  lamellated 
capsule.  X  380.  (After  Sobotta.) 


nective  tissue.  The  nerve  fiber  on  entering  the  core  loses  its  medullary 
sheath,  and  after  traversing  a  greater  or  less  portion  of  the  core  divides 
into  two  to  five  branches  which  end  near  the  distal  pole  in  a  disk-like 
expansion.  In  its  course  through  the  core,  the  nerve  fiber  gives  off  fine 
lateral  twigs  (Sala,  Retzius). 

The  connective  tissue  sheath  consists  of  a  granular  protoplasm  which 


NERVE  ENDINGS  IN  CONNECTIVE  TISSUE 


169 


is  permeated  by  densely  felted  spiral  fibers  (Sala)  and  is  divided  into 
ten  to  fifty  concentric  lamellae  by  lines  of  flattened  connective  tissue 
cells  and  fibers.  According  to  Schwalbe,  however,  these  cells  form  an 
endothelioid  coat  on  either  surface  of  each  lamella.  Lamellar  corpuscles 
are  occasionally  compound,  two  or  more  adjacent  corpuscles  being  sup- 
plied by  branches  of  the  same  nerve  fiber. 

Lamellar  corpuscles  are  found  in  large  numbers  in  the  subcutaneous 
tissue  of  the  finger  tips  and  of  the  penis,  as  well  as  in  the  skin  of  other 
parts,  in  the  mesentery  and  the  connective 
tissue  of  neighboring  organs,  e.g.,  the 
pancreas,  in  the  prevertebral  connective 
tissue  of  the  abdomen  and  mediastinum, 
near  the  walls  of  the  large  blood-vessels, 
in  the  serous  membranes, — pleura,  peri- 
cardium, peritoneum — in  the  periarticular 
connective  tissue  and  periosteum,  in  the 
sheaths  of  the  larger  nerve  trunks,  and  in 
the  connective  tissue  of  the  thyroid  gland 
and  of  the  skeletal  muscles. 

5.  The  Corpuscles  of  Herbst  (Key- 
Retzius  Corpuscles}. — The  corpuscles  of 
Herbst  are  similar  in   structure  to  the 
lamellar  corpuscles  except  that  the  core 
which  surrounds  the  axial  nerve  fiber  con- 
tains cuboidal  tactile  cells.     They  occur 
only  in  the  cere  of  aquatic  birds. 

6.  The     Corpuscles    of    Grandry 
(Merkel's    Corpuscles}. — The    corpuscles 
of  Grandry,  also  found  only  in  aquatic 
birds,  contain  several  tactile  cells  of  ecto- 
blastic  origin  similar  to  those  found  -in 

the  epidermis.  Each  cell  is  in  relation  with  a  ring  or  meniscus  formed 
by  the  expanded  end  of  a  nerve  fiber.  The  whole  is  included  within  a 
tli in  connective  tissue  capsule  and  may  be  regarded  as  a  compound  tactile 
cell  occurring  in  connective  tissue. 

7.  The  Golgi-Mazzoni  Corpuscles.— The  Golgi-Mazzoni  corpuscles 
described  by  Ruffini  (Arch.  ital.  de  biol.,  1894)  somewhat  resemble  the 
Facinian  corpuscles  in  that  they  possess  a  lamellar,  though  relatively 
very  thin,  connective  tissue  sheath  and  a  central  granular  core.    The  core, 
however,  is  relatively  excessive  in  size,  and  the  entering  nerve  fiber 


FIG.  188. — A  PAPILLA  OF  THE 
DUCK'S  TONGUE,  CONTAINING 
A  CORPUSCLE  OP  GRANDBY. 

The  corpuscle  contains  four 
large  cells,  between  which  are  the 
tactile  menisci  of  the  nerve  end- 
ing, n,  nerve.  Highly  magnified. 
(After  Merkel,  from  Kolliker.) 


170          PERIPHERAL  NERVE  TERMINATIONS:  END  ORGANS 

breaks  into  a  number  of  branches  with  discoid  terminal  expansions  simi- 
lar to  those  found  in  the  nerve  endings  of  Golgi  in  the  tendons.    They 


FIG.  189. — GOLGI-MAZZONI  CORPUSCLES  FROM  THE  SUBCUTANEOUS  TISSUE  OF  THE 
TIP  OF  THE  FINGER.     (After  Ruffini.) 


occur  also  in  the  corium  of  the  skin  in  certain  regions  (e.g.,  the  external 
genitalia,  finger  tips),  and  in  the  conjunctiva  and  the  periosteum. 


NERVE  ENDINGS  IN  MUSCLE  AND  TENDON 


171 


NERVE   ENDINGS   IN   MUSCLE    AND    TENDON 

A.    VOLUNTARY  STRIPED  MUSCLE 

1.  Motor  End  Plates. — These  organs  form  the  intramuscular  end- 
ings of  motor  axons  whose  cell  bodies  are  found  in  the  ventral  horns  of 
the  gray  matter  of  the  spinal  cord.  The  efferent  fibers  reach  the  muscle 
through  the  many  cerebrospinal  nerve  trunks.  On  entering  the  muscle 


fk 

92m 

/  ^Si± 


FIG.  190. — MOTOR  XEKVE  ENDINGS  IN  STRIATED  MUSCLE. 

A,  from  a  lizard;  B,  from  the  guinea-pig;  C,  from  the  hedgehog.  A  and  C  are  sur- 
face views;  in  B  the  end  plate  is  seen  in  profile,  a,  muscle  fiber;  b,  nerve  fiber;  c,  nerve 
ending  in  the  form  of  a  'brush';  d,  the  sole  plate;  e,  sarcolemma.  A,  X  160;  B,  X  700; 
C,  X  1200.  (After  Bohm  and  von  Davidoff.) 

these  nerves  form  a  plexus  in  the  perimysium  from  which  nerve  fibers 
are  distributed  within  the  muscle  bundles.  Here  they  form  an  abundant 
plexus  of  branching  nerve  fibers  within  the  endomysium,  the  ultimate 
branches  being  of  sufficient  number  to  supply  one  or  more  terminal  nerve 
fibers  to  each  muscle  fiber. 


172 


PERIPHERAL  NERVE   TERMINATIONS:    END   ORGANS 


At  the  surface  of  the  muscle  fiber  the  nerve  fiber  loses  its  medullary 
sheath,  its  neurolemma  becomes  continuous  with  the  sarcolemma  of  the 
muscle  cell,  and  its  naked  axis  cylinder  divides  into  two  to  five  branches, 
which  end,  often  after  repeated  subdivision,  in  flattened  terminal  disks, 
distributed  in  mammals  over  a  limited,  in  amphibians  over  a  broad  area, 
but  which  never  completely  encircle  the  cylindrical  muscle  cell. 

The  terminal  expansions  of  the  axon  rest  upon  a  granular,  slightly 
raised  sole  plate  which  contains  many 
ovoid  muscle  nuclei,  the  sole  nuclei. 

2.  Muscle  Spindles  (N euro  mus- 
cular Spindles,  N euromuscular  End 
Organs'). — These  are  sensory  ncrrr 

fgj^R  endings   which    are    concerned    with 

c  t*8''  ^  a  the  so-called  muscle  sense.     They  are 

*"T^%^    ~*z     »   *p^.      especially  numerous  in  the  extrinsic 
A     7~'^  muscles  of  the  tongue,  in  the  small 

muscles  of  the  hand  and  foot,  and  in 
the  intercostal  muscles  (Huber,  Amer. 
Jour,  of  Anat.,  1902).  They  have 
not  been  found  in  the  muscles  of  the 
diaphragm.  A  detailed  description  of 
the  developing  neuromuscular  spin- 
dle in  the  extrinsic  eye  muscles  of  the 
pig  has  recently  been  given  by  Sutton 
(Am.  Jour.  Anat.,  18,  1,  1915).  He 
describes  a  coarsely  granular  'plaque,' 
different  from  both  muscle  and  nerve, 
which  he  inclines  to  regard  as  an 

'intermediary  structure,'  perhaps  a  receptor  substance  analogous  to  the 
sole  plate  of  motor  endings. 

A  muscle  spindle  contains  from  five  to  twenty  striated  muscle  fibers 
of  small  size,  and  an  almost  equal  number  of  nerve  fibers.  The  whole 
is  inclosed  within  a  connective  tissue  capsule  of  considerable  thickness. 
The  bundle  of  intrafusal  muscle  fibers  is  again  surrounded  by  a  delicate 
axial  sheath  of  connective  tissue  which  is  united  to  the  capsule  by  bands 
of  fine  fibrous  tissue  which  span  the  broad  periaxial  lymphatic  space. 
The  larger  of  these  fibrous  bands  support  the  nerve  fibers,  on  their  way 
to  the  intrafusal  muscle  cells,  together  with  several  small  blood-vessels. 
The  muscle  spindles  form  long  fusiform  bodies  (from  1  to  5  milli- 
meters in  length)  whose  muscle  fibers  at  the  pole  of  the  spindle  may  be 


FIG.  191. — A  MUSCLE  SPINDLE  FROM 
THE  PSOAS  MAGNUS  OF  MAN. 

1,  intrafusal  muscle  fibers;  2,  nerve 
fibers;  3,  axial  sheath;  4,  connective 
tissue  capsule;  5,  muscle  fibers  of  an 
adjacent  fasciculus;  6,  peri-axial 
lymphatic  spaces;  7,  blood-vessel. 
Hematein  and  eosin.  X  470. 


NERVE  ENDINGS  IN  MUSCLE  AND  TENDON 


173 


connected  with  the  tendon,  or  they  may  join  other  muscle  fiber  bundles. 
The  muscle  spindles  are  usually  found  in  the  fibrous  septa  of  the  peri- 
mysium.  Compared  with  the  adjacent  muscle  fibers,  the  intrafusal  fibers 
have  a  smaller  diameter,  are  less  distinctly  but  more  coarsely  striped, 
and  contain  some  centrally  located  nuclei. 

Either  one  or  several  nerve  trunks  enter  the  spindle,  usually  near 
its  equator  rather  than  at  its  poles.    The  nerve  fibers  branch  repeatedly 


FIG.  192. — MIDDLE  THIRD  OF  A  TERMINAL  PLAQUE  IN  THE  MUSCLE  SPINDLE  OF  AN 
ADULT  CAT. 

A,  rings;  F,  dendritic  branchings;  S,  spirals.    Chlorid  of  gold  preparation.    Highly 
magnified.    (After  Ruffini.) 


in  the  intracapsular  connective  tissue,  and  finally  pierce  the  axial  sheath 
as  naked  processes  which  form  a  rich  arborization  of  terminal  fibrils 
about  the  intrafusal  muscle  fibers.  Euffini  distinguishes  three  types  of 
terminal  nerve  fibrils:  (1)  annular,  which  form  rings  around  the  muscle 
fibers;  (2)  spiral,  which  are  spirally  twisted  about  the  intrafusal  fibers; 
and  (3)  dendritic  branchings,  in  which  the  axons  break  into  numerous 
irregular  processes  with  laminate  expansions. 

Motor  end-plates  for  the  muscle  fibers  of  the  spindle  as  well  as  sym- 
pathetic vasomotor  nerves  for  its  blood-vessels  have  also  been  demon- 
strated within  the  muscle  spindles. 

That  the  muscle  spindles  are  sensory  and  not  motor  organs  has  been 


174  PERIPHERAL  NEEVE  TERMINATIONS:  END  ORGANS 

demonstrated  by  Sherington  (Jour.  Physiol.,  189-4),  who  found  that  they 
were  not  affected  by  the  muscular  atrophy  following  section  of  the  pe- 
ripheral motor  neurones,  and  by  Horsley  ("Brain,"  1897)  and  others  who 
have  found  that  the  muscle  spindles  are  unaffected  in  cases  of  extreme 
muscular  atrophy  in  man. 

3.  Neurotendinous  End  Organs  (GoJgi  End  Organs,  Tendon  Spin- 
dles).— These  organs  occur  in  the  tendons  of  muscles  near  the  junction 
of  the  tendon  bundles  with  the  muscle  fibers.  They  are  fusiform  in 
shape  and  consist  of  a  thin  lamellar  capsule  of  connective  tissue  which 


FIG.  193. — NEUROTENDINOUS  END  ORGAN  OR  TENDON  SPINDLE  OF  GOLGI. 

fpt,  bundle  of  tendon  fibers;  gH,  medullated  nerve  fiber;  rfnc,  ribbon-like  terminal 
ramifications  of  the  neuraxis;  SR,  node  of  Ranvier.  Moderately  magnified.  (After 
Ciacio.) 

incloses  several  intrafusal  tendon  bundles  of  dense  fibrous  tissue.  A 
narrow  lymphatic  space  intervenes  between  the  capsule  and  the  intra- 
fusal tendon  bundles. 

Nerve  fibers  enter  the  spindle  and  give  off  several  medullated  branches 
which  run  between  the  tendon  bundles  near  the  axis  of  the  spindle. 
These  finally  form  naked  end  fibrils  with  branching  end  plates,  which 
surround  the  tendon  bundles  in  an  annular  or  spiral  manner  (Ciacio, 
Arch.  ital.  de  biol.,  1891).  Since  the  structure  of  the  Golgi  tendon 
spindles  closely  resembles  that  of  the  muscle  spindles,  they  are  probably 
of  similar  function. 

4.  Pacinian  Corpuscles  and  End  Bulbs  of  Krause. — In  addition 
to  the  special  motor  and  sensory  end  organs  described  above, 
Pacinian  corpuscles  and  end  bulbs  of  Krause  are  also  found  in  the  con- 
nective tissue  of  striated  muscles, 


NERVE  ENDINGS  IN  MUSCLE  AND  TENDON 


175 


End  plates  of  'accessory'  non-medullated,  probably  sympathetic, 
fibers  have  also  been  described  in  striped  muscle  (Perroncito,  Huber  and 
De  Witt,  and  Boecke).  Muscle  tonus  is  believed  to  depend  upon  this 
innervation. 

B.     CARDIAC  AND  SMOOTH  MUSCLE 

The  nerves  (sympathetic)  of  the  heart  are  distributed  to  the  cardiac 
ganglia,  whence  non-medullated  fibers  pass  to  all  portions  of  the  organ 
and  form  a  very  rich  plexus  in 
the  intermuscular  connective 
tissue.  Fine  terminal  fibrils 
are  distributed  from  this  plexus 
to  the  muscle  fibers,  upon 
whose  surface  they  end  in  vari- 

FIG.    194. — NERVE    ENDINGS    IN    CARDIAC 
MUSCLE  FROM  THE  HEART  OF  A  CAT. 


a,  muscle  cells;  6,  nerve  fiber.  Methylene 
blue.  Highly  magnified.  (After  Huber  and 
De  Witt.) 


cose  swellings  and  end  knobs. 
While  most  of  these  fibrils  are 
probably  motor  in  function, 
others  which  end  in  the  inter- 
muscular  connective  tissue  are 

more  probably  afferent  (sensory).  Occasional  endings  in  cardiac  muscle 
resemble  the  simpler  motor  end  organs  of  skeletal  muscle. 

In  smooth  muscle, 
plexuses  of  sympa- 
thetic nerve  fibers  oc- 

Fio.  195.-NERVE  ENDINGS  IN  SMOOTH  MUSCLE,  FROM      cur   in   the  intervals 
THE  INTESTINE  OF  A  CAT.  between  the  bundles 

of  muscle  cells.  Sec- 
ondary plexuses  of 
naked  fibrils  are 

found  among  the  muscle  cells,  and  from  this  plexus  fine  lateral  fibrils 
are  distributed  to  the  muscle  cells,  upon  whose  surface  they  end  in  smalt 
terminal  granules  or  end  knobs.  Many  of  the  nerve  fibers  in  smooth 
muscle  are  undoubtedly  of  sensory  function. 

The  nerve  endings  and  the  distribution  of  the  peripheral  nerve  fibers 
in  the  various  organs  of  the  body  are  more  fully  described  in  the  several 
chapters  devoted  to  those  organs. 


a,  muscle  cell;  b,  nerve  fiber.    Methylene  blue 
magnified.    (After  Huber  and  De  Witt.) 


Highly 


CHAPTER   VII 
THE   BLOOD   VASCULAE   SYSTEM 

» This  system  includes  the  heart,  arteries,  capillaries,  and  veins. 
These  structures  form  a  continuous  set  of  branching  tubes,  which  convey 
the  blood  from  the  heart,  through  the  arteries  and  capillaries,  and  back 
again  through  the  veins  to  the  heart.  In  the  capillaries  a  portion  of  the 
blood  plasma  transudes  into  the  tissue  spaces,  where  it  forms  the  tissue 
juices,  and  from  which  it  is  returned  to  the  blood  by  the  lymphatic  ves- 
sels, the  terminal  branches  of  which  empty  into  the  subclavian  veins. 
This  entire  vascular  system  is  completely  lined  by  a  single  layer  of 
flattened  epithelial  cells,  the  endothelium.  The  cells  are  united  edge  to 
edge  by  an  intercellular  cement  substance,  to  form  a  continuous  mem- 
brane throughout  the  entire  system.  The  blood-vessels  include  the  ar- 
teries, capillaries,  and  veins,  and  these,  together  with  the  heart,  will 
form  the  subject  of  the  present  chapter.  The  lymphatic  vessels  (lymph 
vascular  system)  will  be  described  in  connection  with  the  lymphatic  sys- 
tem. The  blood  and  lymph  vessels  together  with  their  contents  comprise 
the  vascular  tissue. 

ARTERIES 

'  The  arteries  convey  the  blood  from  the  heart  to  all  the  tissues  of 
the  body.  They  are  therefore  almost  universally  present,  but  vary  in 
size  from  the  aorta  down  to  minute  unnamed  vessels  of  microscopic 
caliber.  They  are  divisible,  according  to  size,  into  the  large,  medium- 
sized,  and  small  arteries,  the  arterioles,  and  what  may  be  termed  the 
arterial  capillaries,  or  precapillary  arteries.  The  large  arteries  include 
only  the  aorta  and  the  largest  of  its  immediate  branches  (innominate, 
common  carotids,  subclavians  and  common  iliacs),  and  the  pulmonary 
artery, — the  conducting  arteries;  the  medium  sized  (distributing)  ar- 
teries comprise  nearly  all  the  remaining  named  arteries  of  the  body; 
small  arteries,  arterioles,  and  precapillary  arteries  include  those  un- 

176 


AKTUKLKS  17? 

named  arteries  which  are  to  be  found  in  nearly  all  of  the  organs  and 
tissues  of  the  body. 

Medium-sized  Arteries. — A  medium-sized  artery  will  be  first  de- 
scribed, as  presenting  the  typical  arterial  structure.  Such  a  vessel  con- 
sists of  three  coats: 

1.  The  internal  coat — tunica  intima,  or  interna. 

2.  The  middle  coat — tunica  media. 

3.  The  external  coat — tunica  adventitia,  or  externa. 

The  internal  coat,  tunica  intima,  presents  three  layers,  the  innermost 
being  the  layer  of  endothelial  cells,  the  outermost  a  layer  of  elastic  tissue, 
the  fenestrated  coat  of  Henle,  or  internal  elastic  membrane;  between 

these   is  a   delicate  fibrous  ^^ 

membrane    or    tunica    pro-  ;        .    ^  .  • : -^^V-vsr=~v»C  *' 

pria,  which  constitutes  the  . ;.,,: .•-:-•'•/" '''-',:'-['  ^:^^3\\ *\VA', 

middle  layer.     This  layer  is  '"-    .;/;":-/> ':':.-.^                   ^^j^X\\v. 

rrgardcd    by    some    as    I  he  .                                                "'^iV'c; 

product  of  the  cndothelium.  t  '^',','i'i & 

The  endothelium  com- 
prises only  a  single  layer  of  <£)§3  ' 
flattened  or  squamous  cells.  .  v%*'\\ 
placed  edge  to  edge  1o  form  ,  '  '^'\i 
a  continuous  membrane  of  <  • " -HxC v  '';'':;'''"'•  -/ 
simple  pavement  epithelium.  '  "  %j%j?&^  n 
These  cells  are  irregularly 

polygonal   in   outline,   with  FIG.  196. — A  SMALL  ARTERY  FROM  THE  CON- 

serrated  margins,   .,„!  are  ™  ? -^  «  ™E  *~  C™ 

somewhat  elongated  in  the 

f  .  a,  tunica  ad ventitia;  x,  tunica  mtima;  m,  tunica 

direction  ot  the  axis  of  media;  n>  a  gmall  non-medullated  nerve  trunk; 
the  vessel.  They  are  loosely  v,  a  minute  venule.  Hematein  and  eosin.  X  370. 
attached  to  the  elastic 

membrane  by  the  middle  layer  of  fine  fibrillar  connective  tissue,  in  whose 
ground  substance  small  branching  connective  tissue  cells  are  found.  The 
thickness  of  this  connective  tissue  layer  varies  proportionately  to  the 
size  of  the  vessel.  In  the  largest  arteries  it  increases  in  amount  also 
with  age,  becoming  especially  well  developed  in  the  aorta.  In  the  smaller 
arteries  and  in  certain  of  the  larger,  e.g.,  external  iliacs,  and  the  main 
branches  of  the  abdominal  aorta,  it  is  so  scant  as  to  be  essential- 
ly lacking.  The  thickening  of  the  intima  in  the  aorta  coincident 
with  increasing  age  is  commonly  interpreted  as  a  compensatory 
mechanism  necessitated  by  the  increasing  diameter  of  the  vessel 


178  THE  BLOOD  VASCULAR  SYSTEM 

due   to  loss   of  elasticity  resulting  from  a    transformation  of   elastin 
into  elacin. 

The  internal  elastic  membrane  is  a  layer  of  elastic  tissue,  consisting 
of  an  intimately  united  fibrous  mass,  which  completely  encircles  the 
artery.  In  the  smaller  vessels  the  elastic  fibers  of  this  layer  form  only 
a  reticulated  structure,  hut  in  the  larger  arteries  they  are  so  abundant 
and  so  closely  interwoven  as  to  form  a  complete  membrane,  which  can 
be  readily  stripped  from  the  subjacent  tissue.  If  the  membrane  thus 
prepared  is  examined  microscopically,  it  will  be  found  to  present  numer- 
ous small  openings  at  points  where  the  elastic  tissue  is  deficient.  It  is 
this  appearance  which  led  to  its  description  as  a  'fenestrated  membrane/ 
The  internal  elastic  membrane  is  intimately  united  to  the  tunica  media, 
upon  which  it  rests;  in  fact,  it  may  perhaps  be  better  considered  as  the 
innermost  layer  of  this  tunic,  for,  in  the  larger  arteries,  e.g.,  the  aorta, 
it  can  only  with  difficulty  be  distinguished  from  the  adjacent  layers  of 
elastic  tissue  which  form  a  large  portion  of  the  tunica  media  of  these 


The  tunica  media,  or  middle  coat,  contains  smooth  muscle,  sheets 
of  elastic  tissue,  and  a  very  delicate  fibrous  connective  tissue.  The  pro- 
portion of  these  elements  present  in  any  given  artery  varies  with  the 
size  of  the  vessel.  Muscular  tissue  usually  predominates,  but  in  the 
larger  arteries  elastic  tissue  is  so  abundant  as  to  appear  quite  in  excess 
of  the  muscular ;  in  the  smaller  arteries,  however,  the  muscular  tissue  is 
by  far  the  more  abundant. 

The  smooth  muscle  fibers  are  circularly  disposed  in  the  wall  of  the 
vessel;  they  are  short,  of  irregularly  serrated  outline,  and  are  intimately 
united  with  one  another.  Quite  frequently  the  muscle  fibers  possess  short 
branches  which  interdigitate  with  those  of  neighboring  fibers.  In  the 
larger  vessels  they  are  arranged  in  layers  which  alternate  with  the  sheets 
of  elastic  tissue.  Small  bundles  of  longitudinal  smooth  muscle  fibers 
are  occasionally  found  in  the  outer  portion  of  the  tunica  media. 

The  elastic  tissue  of  the  middle  coat  is  disposed  in  membranous 
sheets  which,  in  the  larger  vessels,  are  embedded  in  a  fine  fibrillar  con- 
nective tissue.  In  these  vessels,  also,  the  fibro-elastic  membranes  thus 
formed  alternate  with  the  layers  of  smooth  muscle,  throughout  the  entire 
thickness  of  the  tunica  media.  In  consequence  of  the  relaxation  of  the 
normal  arterial  tone  and  the  contraction  of  the  muscular  wall  in  rigor 
mortis,  as  seen' in  the  usual  preparations,  these  elastic  layers,  as  well  as 
the  internal  elastic  membrane,  are  thrown  into  wavy  folds. 

The  external  coat,  tunica  adventitia,  consists  chiefly  of  fibrous  con- 


AETERIES 


179 


nective  tissue.  Relatively  few  clastic  fibers  occur  in  this  coat,  and  these 
for  the  most  part  lie  in  its  inner  portion,  adjoining  the  tunica  media. 
In  the  larger  arteries,  when  especially  abundant,  the  elastic  fibers  form 
an  incomplete  layer,  which  may  be  termed  the  external  elastic  membrane. 
Like  the  internal  elastic  membrane,  this  layer  might  well  be  considered  as 


FIG.    197.— THE    EXTERNAL    CAROTID 
ARTERY  OP  A  CHILD. 

a,  tunica  intima,  the  internal  elastic 
membrane  is  prominent;  b,  tunica 
media,  containing  smooth  muscle  and 
several  wavy  layers  of  elastic  tissue; 
c,  tunica  adventitia,  containing  many 
transversely  and  obliquely  cut  elastic 
fibers  and  much  wavy  connective  tissue. 
Photo.  (After  Magrath.) 


JtH'Vr 


FIG.  198. — TRANSECTION  OF  THE  WALL 
OP  THE  AORTA  OF  A  CHILD. 

The  elastic  tissue  is  deeply  stained. 
1,  tunica  intima;  2,  tunica  media,  8, 
tunica  adventitia;  4,  areolar  connective 
tissue.  Weigert's  elastic  tissue  stain  and 
picro-fuchsin.  Photo.  X  64« 


belonging  to  the  tunica  media,  of  which  coat  it  would  then  form  the 
outermost  stratum. 

The  collagenous  fibers  of  the  tunica  adventitia  are  disposed  in  dense 
interlacing  bundles,  to  form  a  firm,  unyielding  coat.  At  the  periphery 
of  the  artery  the  connective  tissue  bundles  of  the  adventitia  intermingle 
with  those  of  the  adjacent  areolar  connective  tissue,  in  which  the  blood- 
vessels are  nearly  always  embedded,  hence  the  outer  boundary  of  this 
coat  is  usually  more  or  less  ill  defined. 

The  fibrous  bundles  of  the  adventitia  are  disposed  somewhat  obliquely 
or  diagonally  about  the  artery,  thus  forming  a  closely  felted  connective 


180 


THE  BLOOD  VASCULAE  SYSTEM 


tissue  network.  Small  nutrient  blood-vessels,  both  arteries  and  veins 
(vasa  vasorum),  and  minute  nerve  trunks  with  occasional  ganglia,  occur 
in  this  coat.  From  these  vasa  et  nervi  vasorum  capillaries  and  fine  nerve 
fibers,  both  sensory  and  autonomic  vasomotor,  are  distributed  to  the  mus- 
cular coat.  Xo  blood- 
vessels are  found  in  the 
tunica  intima.  In  the 
larger  vessels  the  adven- 
titia  may  contain  also  an 
occasional  lamellar  cor- 
puscle. The  adventitia 
contains  abundant  peri- 
vascular  lymphatics. 
Nervi  vasorum  are  said 
to  be  lacking  in  the 
blood-vessels  of  the  brain 
and  spinal  cord. 

General  Characteris- 
tics of  the  Arterial  Wall. 
— The  tunica  media  is 
almost  invariably  the 
thickest  of  the  arterial 
coats.  In  the  medium- 
sized  vessels,  e.g.,  the 
iliac  arteries,  the  adven- 
titia is  often  of  nearly 
equal  thickness,  but  in 
the  smaller  vessels  it  is 
much  thinner.  The  ar- 
terial wall  as  a  whole, 
also,  is  very  thick  as 
compared  with  the  lumen 
of  the  vessel,  and  is  much 
thicker  than  that  of  a  vein  of  corresponding  size. 

The  wall  of  the  larger  arteries  is  relatively  thinner  as  compared  with 
the  lumen  than  is  the  case  with  the  arterioles;  in  the  latter  vessels 
the  thickness  of  the  arterial  wall  often  exceeds  the  diameter  of  their 
lumen.  In  certain  small  arteries,  e.g.,  those  of  the  liver,  even  this  ratio 
may  be  exceeded. 

The  arterial  wall  contracts  firmly  in  rigor  mortis,  hence  the  arteries 


Elastica  interna 


SEndothelial  layer 


Elastic  j  hers 


Media, 


Bundles  of^mooth 
muscle  cells 


Elastica  externa 


Adventitia 


FIG.  199. — PART  OF  A  CROSS-SECTION  OF  THE 
FEMORAL  ARTERY  OF  A  DOG.  X  150.  (From 
Szymonowicz-MacCallum,  "Histology  and  Mi- 
croscopic Anatomy.") 


AETERIES 


181 


after  death  contain  but  little  blood,  and  because  of  the  density  of  the 
tissues  which  compose  their  wall,  these  vessels  retain,  as  a  rule,  their 
cylindrical  form. 

Large  Arteries. — The  largest  arteries  differ  from  the  medium-sized 
type  in  the  excess  of  elastic  tissue  and  relative  deficiency  of  muscle  in 
their  media,  the  extreme  thinness  of  their  adventitia,  and  the  relative 
thinness  of  their  wall,  as  a  whole,  when  compared  with  their  lumen. 
Elastic  tissue  is  especially  abundant  in  all  of  these  vessels;  in  the  media 
it  equals  in  volume  the  muscular  tis- 
sue, in  the  adventitia  it  forms  a  dense 
network  of  clastic  fibers.  In  the 
aorta  and  the  pulmonary  artery  the 
elastic  tissue  surpasses  the  muscular 
in  the  media.  These  vessels  lack  a 
distinct  internal  and  external  elastic 
membrane. 

The  adventitia  of  the  largest  ar- 
teries is  extremely  thin,  that  of  the 
thoracic  aorta  being  not  much  thicker 
than  its  fibrous  tunica  intima;  this 
coat,  therefore,  forms  but  a  small  por- 
tion of  the  vascular  wall  in  vessels  of 
this  type. 

Small  Arteries.— In  the  small  ar- 
teries the  elastic  tissue  is  relatively 
decreased  and  the  smooth  muscle  no- 
ticeably increased.  The  tunica  intima 
of  these  vessels  is  thin,  and  is  limited 

externally  by  an  internal  elastic  membrane,  which  stands  out  promi- 
nently because  of  the  relative  deficiency  of  elastic  tissue  in  the  tunica 
media. 

In  the  tunica  media  of  these  vessels  the  plates  of  elastic  tissue  which 
characterize  the  larger  arteries  are  scarcely  to  be  found.  This  coat  in 
the  small  arteries  contains  very  little  tissue  other  than  smooth  muscle. 

The  external  elastic  membrane  is  indistinct,  and  the  adventitia  is 
not  more  than  one-half  to  two-thirds  as  thick  as  the  tunica  media. 

Arterioles. — The  arterioles  possess  a  relatively  thicker  wall  than  any 
other  vessel  of  the  arterial  system.  Their  tunica  intima  is  thin,  but  little 
fibrous  tissue  being  contained  within  it,  and  the  internal  elastic  mem- 
brane is  represented  only  by  a  very  incomplete  layer  of  elastic  libers. 


FIG. 


200. — TRANSECTION    OP 
CELIAC  Axis  OF  MAN. 


a,  tunica  intima  with  a  prominent 
internal  elastic  membrane;  b,  tunica 
media,  consisting  chiefly  of  smooth 
muscle;  c,  external  elastic  membrane 
in  the  inner  portion  of  the  tunica  ad- 
ventitia. Photo.  (After  Magrath.) 


182  THE  BLOOD  VASCULAE  SYSTEM 

The  tunica  media  of  the  arteriole  forms  two-thirds  to  three-fourths  of 
its  wall,  and  consists  almost  entirely  of  firmly  united  smooth  muscle 
fibers.  The  adventitia,  much  thinner  than  the  media,  contains  bundles 
of  white  fibers  and  delicate  interlacing  elastic  fibrils. 

Precapillary  Arteries. — The  smallest  arterioles  pass  into  what  may 
be  termed  the  precapillary  arteries.  In  these  minute  vessels  the  wall 
consists  of  scarcely  more  than  the  endothelial  lining,  about  which  is  an 
incomplete  layer  of  circular  muscle  fibers,  interspersed  with  occasional 


FIG.  201. — A  GROUP  OP  SMALL  BLOOD-VESSELS. 

A,  small  artery  obliquely  cut;  B,  arteriole  and  venule,  the  latter  filled  with  blood; 
a,  fat  cells.  A  and  B  are  from  the  connective  tissue  of  the  anterior  cervical  region. 
Hematein  and  eosin.  A,  X  HO;  B,  X  550.  C,  a  small  artery  near  the  descending 
aorta  of  man;  the  internal  and  external  elastic  membranes  are  rendered  distinct  by 
the  stain.  Hematein,  Weigert's  elastic  tissue  stain,  and  picro-fuchsin.  X  550. 


collagenous  and  elastic  fibers.  On  approaching  the  capillaries  the  endo- 
thelial tube  is  gradually  laid  bare.  It  is  the  smooth  muscle  which  is 
the  last  of  the  tissues  to  disappear  from  the  arterial  wall,  whereas  be- 
yond the  capillaries  it  is  the  fibrous  tissues  which  are  first  added  to 
the  endothelial  tube  to  form  the  wall  of  the  smallest  venules  (Fig.  207). 

Atypical  Arteries. — Certain  atypical  arteries  differ  markedly  from 
the  typical  structure  above  described. 

The  umbilical  arteries  are  almost  exclusively  muscular,  and  practically 
lack  elastic  tissue.  The  muscle  is  arranged  in  two  distinct  layers :  an  inner 
longitudinal,  and  a  wide  outer  circular;  external  to  these  is  usually  a 


ARTERIES 


183 


FIG.  202. — SEMI-DIA- 
GRAMMATIC ILLUS- 
TRATION OF  SMALL 
BRANCH  OF  PULMO- 
NARY ARTERY  OP 
Ox. 

(After  Piana.)   X70. 


more  or  less  complete  third  layer  of  scattered  bun- 
dles of  longitudinally  arranged  smooth  muscle  cells. 
The  umbilical  vein  is  very  similar  but  contains  more 
elastic  fibers,  and  a  distinct  internal  elastic  mem- 
brane. 

The  cerebral  and  meningeal  arteries  have  very 
thin  walls  and,  exclusive  of  a  relatively  very  well 
developed  internal  elastic  membrane,  contain  but 
little  elastic  tissue. 

The  iliac,  splenic,  renal,  superior  mesenteric  and 
dorsalis  penis  contain  scattered  longitudinal  bundles 
of  muscle  in  the  media  next  the  intima. 

In  the  pulmonary  arteries  the  media  is  excep- 
tionally well  developed.  This  is  the  case  to  an  ex- 
treme degree  in  the  pulmonary  arterioles  of  the  cat. 
The  pulmonary  arteries  and  veins  are  very  similar 
in  structure.  In  the  guinea  pig  and  opossum  the 
media  of  the  arterioles  consists  throughout  of  thick 
oval  segments  of  circularly  disposed  smooth  muscle 

alternating  with  narrow  intervals  where  the  muscle  layer  is  relatively  thin. 
In  ox,  sheep  and  pig  such  segmented  condition  of  the  media  is  modified 
in  that  the  segmentation  is  spirally  disposed. 

The  media  of  the  roots  of  the  aorta 
and  the  pulmonary  artery  consists  largely 
of  cardiac  muscle. 

In  the  subclavian  artery  the  longitu- 
dinal surpasses  the  circular  muscle  in  the 
media.  In  the  arch  of  the  aorta  and  in 
the  upper  portion  of  the  descending  aorta 
longitudinal  muscle  bundles  are  found  in 
the  intima,  media  and  adventitia  (von 
Bardeleben).  The  common  carotid,  com- 
mon iliac  and  common  femoral  (cruralis) 
contain  both  longitudinally  and  spirally 
arranged  muscle  fibers  in  the  media.  In 
general,  where  large  arteries  are  subjected 
to  bendings  the  circular  muscle  fibers  are 
reinforced  by  oblique  (spiral)  and  longi- 
tudinal bundles  in  the  media.  This  is 
conspicuously  the  case  in  the  common 
iliacs,  the  popliteal,  and  the  brachial  ar- 
teries (MacCordick,  Anat.  Anz.,  44,  11, 
1913). 


FIG.  203. — SEMI-DIAGRAMMATIC 
ILLUSTRATION  OF  DIVIDING 
SMALL  BRANCH  OF  PULMONARY 
ARTERY  OF  GUINEA-PIG. 


Pulmonary  arterioles   of   opos- 
sum are  almost  identical.   X  50. 


181  THE  BLOOD  VASCULAR  SYSTEM 

Comparison  of  Large  and  Small  Arteries. — The  larger  arteries  are 
typically  elastic,  the  smaller  typically  muscular.  In  the  larger  vessels 
the  elastic  tissue  forms  about  one-half  of  the  entire  wall;  toward  the 
smaller  arteries  this  tissue  progressively  diminishes  until,  in  the  ar- 
terioles,  it  is  limited  to  an  incomplete  internal  elastic  membrane,  the 
homologue  of  the  complete  elastic  coat  or  fenestrated  coat  of  Henlc, 
which  is  found  only  in  larger  vessels. 

The  smooth  muscle,  on  the  other  hand,  increases  in  relative  amount 
from  the  larger  to  the  smaller  arteries.  While  in  the  largest  vessels  it 
forms  not  more  than  one-third,  in  the  arterioles  it  represents  about  three- 
fourths  of  the  arterial  wall. 

In  the  largest  arteries  the  adventitia  is  relatively  very  thin.  That 
of  the  medium-sized  vessels  is  much  thicker,  and  the  ratio  of  connective 
tissue  as  found  in  the  wall  of  these  vessels  remains  fairly  constant  down 
to  the  arterioles.  In  the  wall  of  the  precapillary  arteries  connective 
tissue  is  very  scanty. 

CAPILLARIES 

The  capillaries  are  minute  tubes,  5  to  13  p  in  diameter,  which,  in 
nearly  all  the  tissues  of  the  body,  connect  the  arteries  with  the  veins. 
Their  wall  is  formed  by  a  layer  of  endothelial  cells  which  on  the  one 
hand  is  continuous  with  the  endothelial  lining  of  the  arteries,  on  the 
other  hand  with  that  of  the  veins. 

As  a  rule  there  are  neither  muscle  fibers  nor  connective  tissue  in 
the  wall  of  the  true  capillaries;  occasionally,  however,  very  fine  isolated 
circumferential  elastic  fibers  encircle  the  endothelial  tube.  In  the 
minute  arterioles  and  venules,  which  are  about  to  terminate  in  or  take 
origin  from  the  true  capillaries  and  which  have  been  described  as  pre- 
capillary arterioles  and  venules,  a  very  thin  layer  of  muscle  fibers  or  of 
connective  tissue  is  added  to  the  endothelial  wall  of  the  capillary.  On 
the  arterial  side  the  muscle  is  the  first  tissue  to  be  thus  added,  on  the 
venous  side  the  fibrous  connective  tissue  is  the  first  to  appear. 

The  endothelium  of  the  capillary  wall  consists  of  flattened  plate- 
like  cells  which  are  joined  edge  to  edge  by  cement  substance.  These 
cells  are  somewhat  elongated  in  the  axis  of  the  vessel,  the  shape  of  the 
cell,  as  in  the  arteries  and  veins,  depending  upon  the  size  of  the  vessel, 
— the  smaller  the  vessel  the  more  elongated  its  endothelial  cells.  The 
margins  of  these  cells  are  extremely  irregular,  hence  they  present  a  wavy 
or  serrated  outline. 


FIG.  204. — THE  CAPILLARY  NETWORK  CONNECTING  AN  ARTERIOLE  AND  VENTJLE 
OF  THE  OMENTUM  OF  A  YOUNG  RABBIT. 

The  blood-vessels  have  been  injected.  The  discolorations  at  I  and  I  are  due  to  the 
presence  of  lacteals  beneath  the  endothelium;  at  I'  and  I'  these  are  surrounded  by  the 
capillary  network,  a,  arteriole;  v,  venule.  Considerably  magnified.  (After  Ranvier.) 


FIG.  205. — CAPILLARY  VESSEL  OF  THE  FROG'S  MESENTERY. 

Treated  with  nitrate  of  silver  to  show  the  outlines  of  the  endothelial  cells.    Highly 
magnified.     (After  Ranvier.) 

13  185 


186 


THE  BLOOD  VASCULAE  SYSTEM 


Although  the  endothelial  cells  of  the  capillary  wall  appear  to  be 
firmly  united  to  one  another,  yet  they  are  capable  of  being  separated 

sufficiently  to  permit  the  ready 
passage  of  white  blood-cells 
through  the  capillary  wall,  by 
diapedesis.  The  capillary  wall 
does  not  appear  to  be  an  inactive 
factor  in  this  process,  for  inert 
pigment  granules  may  also  pene- 
trate the  wall  of  these  vessels, 
the  endothelial  cells  immediately 
closing  the  aperture  which  is 
thus  formed.  Nevertheless,  pure- 
ly mechanical  means,  e.g.,  in- 
creased blood-pressure,  appear 
also  to  favor  this  process.  The 
openings  which  are  formed  be- 
tween the  endothelial  cells  by 
diapedesis  of  blood-cells  are  very 
transitory;  they  are  almost  im- 
mediately closed  by  the  activity 
of  the  endothelium.  Such  tran- 
sitory breeches  of  the  capillary 
wall  are  termed  stigmata. 

The  capillaries  branch  and 
anastomose  with  one  another  to 
form  networks,  the  outlines  of 
whose  meshes  vary  according  to 
the  tissue  in  which  they  occur. 
FIG.  206.— Two  SINUSOIDAL  VESSELS  FROM     jn  such  tissiies  as   muscle  and 
THE  MEDULLA  OF  THE  HUMAN  ADRENAL. 


Each  contains  the  outline  of  a  single  red 


nerve    they    form    elongated 


blood   corpuscle  for  comparison    of    size,  meshes    whose    long    axes    are 

At  a,  a  small  vein  is  shown;  it  is  filled  with  parallel  to  those  of  the  muscle 

blood  and   possesses  a    much  thicker  waU  Qr   nerye    fib  in   the   b 

than  that  of  the  sinusoids.    Hematein   and 

eosin.    X  410.  more  areolar  tissues  they  form 

large  meshes  of  irregular  form; 

while  in  the  capillary  membranes,  as  in  the  walls  of  the  pulmonary 
alveoli,  they  are  disposed  in  a  close  net,  the  diameter  of  whose  meshes 
scarcely  exceeds  that  of  the  capillaries. 

With  but  few  exceptions  capillaries  occur  in  all  the  tissues  of  the 


VEINS 


187 


body.  In  epithelium  and  in  cartilage  there  are  no  blood-vessels  of  any 
kind,  and  in  the  splenic  pulp  it  is  doubtful  if  true  capillaries  occur.  In 
certain  tissues-  large  vascular  spaces  occur,  which  are  comparable  to 
the  capillaries  in  that  their  wall  consists  of  scarcely  more  than  the  endo- 
thelial  tube,  but  which  differ  from  the  true  capillaries  in  the  extreme 
size  of  their  lumen.  These  vessels  have  been  described  by  Minot  (Jour. 
Bost.  Soc.  of  Med.  Sc.,  1900)  as  sinusoids.  They  are  found  in  the  erectile 
tissues,  adrenals,  coccygeal  gland,  parathyroids,  in  the  maternal  placenta, 
and  in  the  fetal  liver,  heart,  pronephros,  and  mesonephros.  They  differ 
from  capillaries  also  in  that  they  generally  do  not  connect  arteries  and 
veins,  but  are  either  exclusively  arterial  or  venous.  In  the  adult  only 
venous  sinusoids  occur.  Retia  mirabilia  are  capillary  plexuses  on  ar- 
terioles  or  venules;  the  best  example  of  a  rete  mirabile  in  the  human 
body  is  the  arterial  capillary  plexus  on  the  efferent  glomerular  arteriole 
of  the  kidney. 

VEINS 


The  blood  having  passed  the  capillaries,  enters  the  smallest  radicals 
of  the  venous  system,  the  precapillary  venules,  and  passes  thence  through 
the  venules  to  the  larger  veins.  The  pro-  A  B 

gressive  increase  in  the  caliber  of  these  suc- 
cessive vessels  is  accompanied  by  a  corre- 
sponding increase  in  the  thickness  of  their 
wall.  Thus,  while  the  endothelial  tube  alone 
composes  the  capillary  wall,  the  endothelium 
of  the  precapillary  venule  is  encircled  by  a 
delicate  connective  tissue  membrane.  In  the 
venule  occasional  smooth  muscle  fibers  are 
added  to  the  wall  of  the  smaller  vessel,  and 
in  the  vessels  of  this  caliber  the  fibrous  tis- 
sues have  been  so  increased  that  the  vascular 
wall,  as  in  the  artery,  can  be  said  to  possess 
three  coats. 

Precapillary  Venules.— The  wall  of  the 
precapillary  venule  consists  of  the  endo- 
thelial  lining,  which  is  surrounded  by  a 
very  delicate  connective  tissue  membrane 
in  which  are  very  few  elastic  and  white 
fibers. 


FIG.     207.  —  PRECAPILLARY 
VENULE  AND  ARTERIOLE. 

The  lighter  nuclei  are  those 
of  the  endothelium.  The 
darker  nuclei  in  the  venule 
are  in  connective  tissue  cells; 
in  the  arteriole  they  are  in  the 
muscle  cells.  A,  venule;  B, 
arteriole.  Partly  diagram- 
matic. Highly  magnified. 


188 


THE  BLOOD  VASCULAR  SYSTEM 


Venules.— In  the  venule  the  tunica  intima  consists  of  little  more 
than  the  endothelial  lining.  Its  media  and  adventitia  are  not  as  yet 
distinctly  differentiated,  the  former  being  distinguished 'only  by  the  in- 
complete layer  of  circularly  disposed  smooth  muscular  fibers.  The  ex- 
tremely thin  adventitia  is  composed  almost  wholly  of  white  fibers,  the 
greater  part  of  which  are  circularly  disposed.  Very  few  elastic  fibers 
occur  even  in  vessels  of  this  size. 

Small  Veins. — In  the  small  veins"  the  three  coats  are  fairly  distinct, 
the  vascular  wall  being,  however,  much  thinner  than  in  the  artery  of 
corresponding  size. 

The  endothelium  of  the  tun'ca  intima  is  supported  by  a  very  delicate 
connective  tissue  membrane  which  as  yet  contains  but  few  elastic  fibers. 


FIG.  208. — TKANSECTION  OF  AN  ARTERIOIE  AND  VENULE. 
X  250.     (After  Schafer.) 

The  tunica  media  consists  of  a  thin  layer  of  circularly  arranged 
smooth  muscle  fibers  intermingled  with  a  delicate  fibrous  tissue;  elastic 
fibers  are  relatively  scarce.  The  adventitia,  though  considerably  the 
thickest  of  the  three  coats,  is  as  yet  a  thin  membrane.  It  consists  of 
fibrous  connective  tissue,  elastic  fibers  being  scarcely  demonstrable  except 
by  means  of  the  specific  stains  for  this  tissue. 

Larger  Veins. — The  wall  of  the  larger  veins  closely  resembles  that  of 
the  corresponding  artery,  except  that  the  venous  wall  is  much  thinner 
and  contains  far  less  elastic  tissue.  The  tunica  intima  of  the  medium 
and  lar^e  veins  presents  a  lining  endothelium,  a  thin  layer  of  delicate 
connective  tissue  fibers,  and  an  incomplete  internal  elastic  membrane. 
The  last  named  is  never  so  prominent  as  in  the  artery. 


VEINS  189 

The  tunica  media  contains  smooth  muscle  fibers,  the  most  of  which 
are  circularly  arranged.  A  somewhat  smaller  proportion  of  delicate 
connective  tissue  completes  this  coat. 

The  media  is  best  developed  in  veins  of  the  lower  extremities;  it 
forms  a  thinner  layer  in  veins  of  the  upper  extremities,  and  is  rela- 
tively scant  in  the  large  veins  of  the  abdominal  cavity. 

The  adventitia  of  the  larger  veins  consists  of  interlacing  bundles  of 
dense  white  fibers,  among  which  is  a  network  of  fine  elastic  fibers.  Occa- 


FIG.  209. — TRANSECTION  OF  THK  WALL  OF  THE  HUMAN  VENA  CAVA. 

a,  tunica  intima;  b,  tunica  media;  c,  tunica  adventitia.  The  inner  portion  of  the 
tunica  adventitia  contains  numerous  bundles  of  longitudinal  smooth  muscle  fibers 
which  have  been  cut  across.  Hematein  and  eosin.  X  90. 

sional  small  bundles  of  longitudinal  smooth  muscle  fibers  occur  in  the 
adventitia  of  the  largest  veins.  In  these  vessels  also,  a  very  incomplete 
external  elastic  membrane  may  be  demonstrated  by  the  specific  stains  for 
elastic  tissue. 

Nerve  fibers  and  minute  blood-vessels,  vasa  vasorum,  occur  in  this 
coat  and  distribute  their  terminal  branches  to  the  two  outer  coats  of  the 
vessel.  The  intima  of  the  vein,  as  in  the  artery,  is  non-vascular.  The 
venae  vasorum  of  veins  empty  directly  into  the  lumen. 

Atypical  Veins. — In  certain  tissues  the  veins  present  noticeable  de- 
partures from  the  typical  structure.  Longitudinal  muscle  fibers  are  found 
in  many  of  the  larger  veins  of  the  abdominal  and  thoracic  cavities. 


190  THE  BLOOD  VASCULAR  SYSTEM 

The  cephalic,  basilic,  mesenteric,  iliac,  femoral,  saphenous,  uterine 
and  the  dorsalis  penis  veins  contain  small  longitudinal  bundles  in  the 
intima.  Certain  veins,  e.  g.,  saphenous,  femoral,  and  popliteal,  contain  a 
layer  of  longitudinal  muscle  in  the  intimal  portion  of  the  media. 

The  adrenal  veins  contain,  almost  exclusively,  longitudinal  muscle 
fibers,  and  in  the  renal,  suprarenal,  portal,  splenic  and  phrenic  veins  and 
the  inferior  vena  cava  these  fibers  form  the  greater  portion  of  the  tunica 
adventitia. 

In  the  pulmonary  veins  the  circular  muscle  fibers  are  highly  developed, 
the  tunica  media  of  these  veins  almost  equaling  in  thickness  that  of  the 
corresponding  pulmonary  artery.  As  in  other  large  veins,  however,  elastic 
tissue  is  notably  deficient  in  the  tunica  media  of  the  pulmonary  veins. 
The  muscle  of  the  roots  is  partially  of  the  cardiac  type. 

The  tunica  media  of  the  largest  veins,  e.  g.,  the  venae  cavae,  jugular, 
innominate  and  subclavian,  contain  much  fibrous  and  considerable  elastic 
tissue,  the  latter  often  forming  incomplete  membranous  layers,  which  alter- 
nate with  the  muscle,  as  in  the  arteries.  Such  structure  is,  however,  limited 
to  the  very  largest  of  the  veins.  In  the  superior  vena  cava  and  the  hepatic 
vein  the  media  is  practically  replaced  by  adventitia. 

The  cranial  veins  (cerebral  and  meningeal)  are  conspicuous  for  the 
almost  entire  absence  of  muscle  from  their  walls,  the  large  meningeal 
sinuses  being  surrounded  by  a  dense  fibrous  coat  derived  from  the  dura 
mater,  and  lined  by  the  usual  endothelium.  In  the  veins  of  the  retina  also, 
and  those  of  bones,  a  media  is  essentially  lacking. 

The  venous  spaces  of  the  erectile  tissues  have  already  been  mentioned 
as  presenting  to  some  extent  the  sinusoidal  type  of  structure,  these  large 
venous  cavities  possessing  an  extremely  thin  wall,  in  structure  scarcely 
more  than  endothelial  lining.  The  afferent  artery  projects  into  the  broad 
vascular  lumen,  from  which  the  efferent  vein  makes  its  exit. 


Comparison  of  the  Larger  and  the  Smaller  Veins. — Comparing 
the  larger  with  the  smaller  veins,  the  excess  of  elastic  and  muscular  tis- 
sue in  the  former  is  most  noticeable.  In  the  absence  of  specific  stains, 
elastic  tissue  can  scarcely  be  recognized  in  the  venules  and  smaller  veins. 
In  the  medium-sized  vessels  it  is  scanty,  but  is  present  in  considerable 
quantity  in  the  largest  vessels. 

The  precapillary  veins  and  venules  contain  scarcely  any  smooth 
muscle.  This  tissue  becomes  more  distinct  in  the  small  veins  and 
steadily  increases  proportionately  to  the  size  of  the  vessel ;  in  the  largest 
veins  it  is  again  relatively  deficient. 

Comparison  of  the  Vein  with  the  Artery  of  Corresponding  Size. 
— The  lumen  of  any  given  artery  is  always  much  smaller  than  the  total 


VEINS  191 

lumen  of  its  venae  comites  (usually  two  in  the  case  of  the  smaller  arter- 
ies, one  vena  comes  in  the  case  of  the  medium-sized),  the  ratio  being 
about  one  to  three.  Hence,  of  any  two  vessels  in  close  proximity  to 
each  other,  the  vein  would  more  likely  possess  the  larger  caliber;  the 
artery,  on  the  other  hand,  would  have  the  thicker  wall. 

As  compared  with  the  arteries,  the  veins  are  notably  deficient  in  elas- 
tic and  muscular  tissue.  In  the  wall  of  most  veins  the  white  fibrous  is 
in  excess  of  all  other  tissues.  For  this  reason  the  adventitia  is  almost 
invariably  the  thickest  of  the  three  coats  of  the  vein,  whereas  in  the 
artery  the  media  is  always  the  thickest  coat. 

The  internal  elastic  membrane,  which  can  be  readily  recognized  even 
in  the  smaller  arteries,  is  limited  to  the  large  veins.  Alternating  layers 
of  elastic  and  muscular  tissues  are  to  be  seen  even  in  the  medium-sized 
arteries,  but  this  arrangement  is  likewise  confined  to  the  largest  of  the 
veins. 

The  wall  of  the  vein  as  a  whole  is  much  thinner  in  proportion  to  its 
lumen  than  that  of  the  corresponding  artery ;  it  is  also  less  rigid.  For 
this  reason  the  wall  of  the  vein  is  much  more  likely  to  collapse  after 
death  than  is  the  thicker  and  more  rigid  arterial  wall.  Because  of  the 
preponderance  of  muscle  in  the  wall  of  the  artery  its  contraction  in 
rigor  mortis  is  more  powerful  than  that  of  the  vein ;  the  vein  therefore  is 
apt  to  be  distended  with  blood  while  the  artery  contains  but  little.  A 
certain  number  of  blood-cells  can  usually  be  found  in  almost  any  type  of 
blood-vessel. 

Valves  occur  at  intervals  of  considerable  length  along  the  course  of 
the  larger  veins.  These  are  not  found  in  the  arteries.  Each  valve  con- 
gists  of  one,  usually  two,  and  occasionally  more  crescentic  folds  or  redupli- 
cations of  the  tunica  intima  between  which  is  a  slightly  increased  amount 
of  connective  tissue,  the  elastic  fibers  of  which  are  more  abundant  on  the 
side  next  the  lumen.  The  valves  therefore  are  suspended  free  in  the 
lumen  of  the  vessel  and  are  covered  on  either  side  with  a  layer  of  endo- 
thelium  which  is  continuous  with  that  lining  the  vein. 

The  valves  open  with  and  close  against  the  blood  current.  They 
occur  generally  distal  to  the  point  of  entrance  of  venous  tributaries.  They 
are  more  abundant  in  the  veins  of  the  extremities  and  are  lacking  in  the 
superior  and  inferior  venae  cava3,  in  the  hepatic,  portal,  renal,  uterine, 
pulmonary,  umbilical,  cerebral  and  meningeal  veins,  in  the  veins  of  bones, 
and  in  veins  of  less  than  2  millimeters  diameter.  They  obviously  assist 
the  flow  of  blood  to  the  heart  against  the  influence  of  gravity.  The  gen- 
eral absence  of  valves  in  the  veins  of  the  abdomen  and  thorax,  and  their 


192 


THE  BLOOD  VASCULAR  SYSTEM 


abundance  in  the  veins  of  the  extremities,  especially  the  lower,  is  prob- 
ably to  be  interpreted  in  terms  of  a  quadrupedal  ancestral  condition. 

The  fact  should  be  borne  in  mind  that  it  is  because  of  their  relative 
infrequency  that  valves  are  not  often  met  with  in  those  transections  of 
the  smaller  veins  which  are  seen  in  nearly  all  microscopical  preparations. 

THE  DEVELOPMENT  OF   BLOOD-VESSELS 


The  earliest  anlage  of  the  blood  vascular  system  is  a  mesenchymalike 
layer,  the  angiollast,  which  appears  between  the  entcderm  and  mesoderm 
at  the  distal  pole  of  the  yolk-sac  (Fig.  210)  at  a  very  early  stage  of  the 
embryonic  development  (1  millimeter,  Minot).  In  this  layer  appear  accu- 
mulations of  rounded  cells  in  the 
form  of  anastomosing  irregular 
solid  cords.  The  peripheral  cells 
become  flattened  to  form  an  endo- 
thelial  tube;  the  central  cells  sepa- 
rate and  scatter  in  the  vessels  as 
primordial  blood-cells  floating  in  a 
plasma,  probably  a  secretion  prod- 
uct of  the  cells.  This  network  of 
primitive  blood-vessels  grows  to- 
ward the  embryo  in  the  shape  of 
tubes  and  solid  nucleated  sprouts 
(angioblast  cords,  Bremer)  and, 
converging  to  form  two  large  ves- 
sels, invades  the  tissue  of  the 
embryo  in  the  region  of  the  de- 
veloping heart  as  the  vitelline 
veins.  Subsequently  other  ves- 
sels, both  arteries  and  veins,  appear  in  the  embryo.  Such  vessels  are  pre- 
ceded by  capillary  plexuses,  as  demonstrated  by  Evans  (Anat.  Rec.,  3,  9, 
1909),  in  which  the  definitive  vessels  arise  as  paths  in  the  original  network 
selected,  enlarged,  and  modified  under  the  influence  of  mechanical  factors 
incident  to  the  flow  of  the  main  stream  of  the  blood.  There  can  be  no 
doubt  that  the  original  anlages  of  the  blood-vessels  arise  by  a  confluence  of 
separate  spaces  (angiocysts), — possibly  always  connected  by  angioblast 
cords, — and  tubes  formed  in  the  angioblast;  likewise  there  is  no  doubt  that 
the  embryonic  blood-vessels  sprout  as  tubes  and  solid  cords  and  thus  grow 
into  adjacent  regions  (Fig.  211).  But  the  features  of  vasculogenesis  con- 
cerning which  there  remain  decided  differences  of  opinion  are  (1)  the 
nature  and  origin  of  the  angioblast,  that  is  whether  of  mesodermal,  ento- 


FIG.  210.— A  13  MM.  HUMAN  EMBRYO. 
The  chorionic  vesicle  is  cut  open,  re- 
vealing  the   embryo    enveloped    in    the 
amnion,  and  the  yolk-sac  (y.s.).      X  1%. 


THE  DEVELOPMENT  OF  BLOOD-VESSELS 


193 


dermal  or  of  dual  origin;  (2)  the  manner  of  origin  of  the  primary  vascular 
stems  in  the  embryo,  whether  by  invasion  through  growth  from  the  extra- 
embryonic  primitive  vascular  area,  or  by  a  process  in  the  body  mesenchyma 
similar  to  that  through  which  the  primitive  vessels  arose  in  the  yolk-sac 
(umbilical  vesicle).  The  evidence  seems  to  favor  the  mesodermal  origin 
of  the  angioblast.  The  advocates  of  vasculogenesis  by  invasion  (Evans, 
Minot,  Bremer  and  others)  regard  the  original  angioblast,  very  early  differ- 
entiated from  mesenchyma, 
as  the  sole  future  source  of 
endothelium,  to  which  is 
ascribed  a  strict  specificity 
throughout  development.  The 
advocates  of  the  in  situ 
method  of  origin  (Maximow, 
Huntington,  Schultze,  Miller 
and  others),  on  the  contrary, 
conceive  early  vasculogenesis 
as  a  process  of  progressive 
fusion  of  tissue  spaces  and 
mesenchymal  cells  involving 
a  continued  differentiation  of 
endothelium  from  mesenchy- 
ma. 

The  total  evidence  seems 
to  favor  the  view  that  in 
earliest  stages  blood-vessels 
may  arise  in  the  mesenchyma 
of  the  embryo  and  that  these 

primitive  stems  may  be  added  to  by  discrete  anlages  all  of  which  may 
fuse  to  form  the  vascular  net  out  of  which  develop  the  future  main 
vessels. 

The  vessels  of  later  embryonic  and  fetal  stages  probably  arise  solely 
as  sprouts  from  these  earlier  stems. 

The  chief  point  of  uncertainty  concerns  the  point  in  time  when  vascu- 
loircnois  Basses  from  a  process  including  sprouting  and  fusion  of  separate 
anla-cs,  to  DIM-  where  extension  is  exclusively  by  terminal  growth.  Both 
arteries  and  veins  have  a  like  origin  in  capillary  plexuses. 

The  final  anastomosing  sprouts  of  endothelium  represent  the  defini- 
tive capillaries.  The  development  of  the  definitive  wall  of  arteries  and 
veins  involves  the  formation  of  extra-endothelial  layers  of  muscular  and 
connective!  tissue  elements  from  the  surrounding  mesenchyme,  and  their 
association  into  the  several  tunics  of  the  various  subdivisions  of  these 


FIG.  211. — '  VASOFORMATIVE  '  CELLS  FROM  THE 
MESENTERY  OF  A  RABBIT  SEVEN  DAYS  OLD. 

g.s.,  red  blood  cells;  n,  nucleus  of  the  vascular 
endothelium;  p,  points  of  growth,  at  which  ex- 
tension occurs.  Highly  magnified.  (After  Ran- 
vier.) 


THE  BLOOD  VASCULAR  SYSTEM 


The  essential  matters  in  the  foregoing  chapter  may  be  summarized 
in  the  following  schemes. 


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pazis-umipaK 

HEART  195 


HEART 

The  wall  of  the  heart  consists  of  interlacing  bundles  of  cardiac  mus- 
cle fibers,  the  myocardium,  which  are  covered  externally  by  the  epicar- 
dium, a  serous  membrane  which  forms  the  visceral  layer  of  the  peri- 
cardium. Internally  the  muscular  wall  of  the  heart  is  lined  by  the 
endocardium,  which  resembles  the  serous  membranes  in  that  it  consists 
of  pavement  epithelium  supported  upon  a  layer  of  fibre-elastic  connective 
tissue.  The  endocardium  lines  all  the  cavities  of  the  heart,  and  its  endo- 
thelium  is  directly  continuous  with  that  of  those  arteries  and  veins 
which  are  connected  with  the  cavity  of  the  heart.  Thus  the  entire 
vftscular  system — heart,  arteries,  capillaries,  lymphatics,  and  veins — may 
be  said  to  be  lined  by  an  uninterrupted  sheet  of  pavement  epithelial  cells, 
the  endothelium. 

Myocardium. — The  muscle  cells  of  the  myocardium  are  so  disposed 
as  to  form  long  fibrous  bundles  which  by  their  figure-of-8  arrangement 
are  interwoven  with  one  another  to  form  a  dense  interlacing  mass  of  mus- 
cle bundles.  (For  detailed  description  see  Mall,  Amer.  Jour.  Anat.,  11,  3, 
1911.)  The  structure  of  these  cardiac  muscle  fibers  has  already  been 
described.  Because  of  the  irregularity  of  their  disposition,  transections 
of  the  cardiac  wall  present  sections  of  muscle  fibers  which  have  been 
cut  in  every  conceivable  direction. 

Between  the  muscle  fibers  is  a  very  delicate  framework  of  fibrous 
connective  tissue,  the  endomysium,  which  surrounds  the  muscle  fibers 
and  supports  the  abundant  capillaries,  arterioles,  and  venules,  with 
which  they  are  supplied.  The  proportion  of  connective  tissue  in  the 
normal  myocardium  as  compared  with  the  muscle  is,  nevertheless,  very 
small. 

In  certain  portions  of  the  myocardium  connective  tissue  is  more  abun- 
dant. Thus  it  is  slightly  increased  in  the  vicinity  of  the  endocardium,  in 
the  papillary  muscles,  and  near  the  bases  of  the  cardiac  valves.  At  the 
surface  of  the  heart,  beneath  the  epicardium,  especially  in  the  various 
grooves  on  the  surface  of  the  heart,  the  connective  tissue  is  still  more 
abundant,  and  may  contain  groups  of  fat  cells.  It  is  through  these 
accumulations  of  connective  tissue  that  the  larger  blood-vessels  are  dis- 
tributed to  the  myocardium. 

Epicardium. — The  epicardium,  like  the  other  serous  membranes, 
consists  of  a  layer  of  pavement  cells,  so  joined  edge  to  edge  as  to  form 
a  complete  mesothelial  coat.  Here  and  there  the  mesothelium  present,  i 


196  THE  BLOOD  VASCULAR  SYSTEM 

small  openings  at  the  angles  between  its  cells;  these  stomata  are  sur- 
rounded by  minute,  finely  granular  cells  and  are  perhaps  connected  with 
the  lymphatic  vessels. 

The  mesothelium  of  the  epicardium  is  supported  upon  a  thin  layer 
of  dense  areolar  tissue  in  which  are  many  small  blood-vessels  and 
lymphatics.  Fibers  from  the  deeper  surface  of  this  layer  are  prolonged 
into  the  myocardium  to  become  continuous  with  its  endomysial  connec- 
tive tissue.  The  larger  of  these  connective  tissue  trabeculas  accompany 
the  branches  of  the  larger  arteries  and  veins  which  are  distributed  to 
the  muscular  wall  of  the  heart. 

Endocardium. — The  endocardium  consists  of  a  lining  membrane  of 
polygonal  cndothelial  cells  supported  upon  a  thin  layer  of  delicate 

fibrous  connective  tissue,  of  en- 
dothelial  origin  (Mall).  In  this 
membrane  is  a  network  of  elas- 
tic fibers,  and  a  small  amount 
of  smooth  muscle.  The  en- 
dothelium  of  this  membrane  is 
continuous  with  that  of  those 
blood-vessels  which  open  from 

212.— THE  PARIETAL  LATER  OF  THE     the   cavities  of  the  heart.      Its 
PERICARDIUM  OF  A  CHILD.  ,.        , .  IP 

connective  tissue  also  forms  a 

a,    mesothelium ;    o,    connective    tissue.  t.  .  .  .       , 

Hematein  and  eosin.    Photo.    X  500.  continuous   layer   with   that   of 

the  tunica  intima  of  these  ves- 
sels; in  fact,  the  three  coats  of  the  cardiac  wall — endocardium,  myocar- 
dium, and  epicardium — might  well  be  compared  with  the  corresponding 
three  coats  of  the  arterial  and  venous  walls — the  intima,  media,  and  ad- 
ventitia.  In  either  organ,  the  inner  coat  consists  of  a  lining  membrane 
of  endothelium,  and  a  supporting  membrane  of  connective  tissue;  muscle 
in  large  part  composes  the  middle  coat,  while  the  outer  coat  is  typically  a 
connective  tissue  layer. 

Valves. — At  the  cardiac  orifices  the  entire  thickness  of  the  endocardium 
is  folded  upon  itself  to  form  a  double  layer,  between  the  folds  of  which 
an  intervening  stratum  of  dense  fibro-elastic  tissue  is  inserted.  These 
endocardial  folds  form  the  cardiac  valves.  The  number  and  shape  of 
their  cusps  are  dependent  upon  the  location.  The  semilunar  valves  of 
the  aortic  and  pulmonary  orifices  consist  of  three  crescentic  endocardial 
folds;  at  the  auriculoventricular  orifices  the  tricuspid  valve  consists  of 
three,  the  bicuspid  or  mitral  of  two,  folds. 

The  margin  of  the  valvular  cusp  or  fold  is  extremely  thin;  just  within 


HEAET 


197 


the  margin,  however,  the  central  mass  of  dense  fibrous  tissue  is  somewhat 
thickened  to  form,  in  each  cusp,  a  dense  rim  which  during  valvular 
closure  secures  the  firm  and  accurate  approximation  of  the  free  margins 
of  adjacent  cusps.  At  the  apex  of  the  valvular  cusp,  where  the  adjacent 
fibrous  margins  of  the  valve  meet,  the  dense  connective  tissue,  particu- 
larly in  the  semilunar  valves,  is  considerably  thickened  to  form  a  nodule, 
the  corpus  arantii.  These  corpora  or  noduli,  in  the  aged,  are  frequently 
subject  to  calcareous  infiltration. 

Muscular  fibers  are  continued  from  the  adjacent  cardiac  wall  into 
the  dense  fibrous  tissue  at  the  base  of  the  valve,  except  in  the  case  of 
the  semilunar  valves  of  the  pulmonary  and  systemic  aortae.  This  muscle 


FIG.  213. — THE  ENDOCARDIUM. 
From  the  ventricular  wall  of  the  heart  of  man.  Hematein  and  eosin.  Photo.  X  469. 

is  generally  non-striped,  and  probably  functions  as  a  sphincter.  The 
lja.se  of  the  valve  is  also  surrounded  by  a  ring  of  fibrous  tissue,  the 
annulus  fibrosus,  whose  interlacing  bundles  are  so  closely  packed  as  to 
give  them  an  almost  cartilaginous  feel.  At  the  auriculoventricular 
orifices,  these  fibrous  rings  are  continuous  with  the  auriculoventricular 
septum,  from  which  the  muscle  bands  of  the  myocardium  take  their 
origin. 

Chordae  Tendineae. — These  are  firm,  unyielding  cords,  composed  of 
parallel  bundles  of  dense  collagenous  fibers,  with  a  few  elastic  fibers,  and 
covered  with  a  very  thin  endocardium  continuous  with  that  of  the  ven- 
tricular wall  and  cardiac  valve.  These  fibrous  bands  unite  the  apices  of 
the  papillary  muscles  to  the  ventricular  surfaces  of  the  mitral  and  tri- 
cuspid  valves.  At  the  apex  of  the  papillary  muscle  the  fibrous  bundles 
of  the  chorda  intermingle  with  the  muscle  fibers,  and  are  continued  into 
the  endomysial  connective  tissue,  which  is  especially  abundant  in  those 


198 


THE  BLOOD  VASCULAR  SYSTEM 


portions  of  the  myocardium.  At  their  valvular  attachment  the  fibrous 
bundles  of  the  chordae  tendineae  turn  almost  at  right  angles,  and  spread 
out,  in  a  somewhat  radial  manner,  to  become  continuous  with  the  dense 
fibrous  tissue  which  forms  the  interior  of  the  valve. 


FIG.  214. — RADIAL  SECTIONS  OF  THE  MITRAL  VALVE,  FROM  THE  HEART  OF  A  MAN. 

A,  from  the  base  of  the  valve  showing  the  extension  into  it  of  cardiac  muscle  fibers 
from  the  wall  of  the  heart;  B,  from  the  mid-region  of  the  valve,  a,  auricular  endo- 
cardium; 6,  muscle  fibers;  c,  dense  fibrous  tissue;  d,  ventricular  endocardium.  Hema- 
tein  and  eosin.  Photo.  X  800. 


Columnae  Carneae. — The  columns?  carneae  are  colnmelliform  projec- 
tions of  the  myocardium  into  the  ventricular  cavity.  They  consist  of 
cardiac  muscle  fibers,  largely  of  the  Purkinje  fiber  variety,  which  are  dis- 
posed in  their  long  axis,  and  are  covered  by  reflections  and  reduplications 
of  the  endocardium.  The  irregular  contour  of  the  ventricular  cavities 
appears  to  be  entirely  due  to  the  projecting  columnge  carneas. 


HEAET 


199 


These  muscular  columns  may  present  any  one  of  three  modes  of 
attachment  to  the  myocardium :  ( 1 )  they  may  be  attached  along  their 
entire  extent;  (2)  they  may  be  attached  only  at  their  two  ends,  the  mid- 
portion  being  free;  (3)  they  may  be  attached  to  the  myocardium  at  one 
end  only,  the  other  end  projecting  into  the  ventricular  cavity  as  a  papil- 
lary muscle,  from  whose  apex  chordae  tendineas  pass  to  the  auriculoven- 


Coronary  Sinus 
Reticulum 


Main  Bundle  of  Hi, 
Pulmonary  Veins 


Sup.  Cava 


Aorta 

Pulmonary  Artery 

(  Muscular  Fibers  Streaming  to 
\     the  Reticulum 
Right  Auricle 

Pars  Mem.  Septi 
5  BifurcationofMainBundleinto 
1   Right  and  Left  Sept.  Branches 
Right  Septal  Branch 


Moderator  Band 


Artery  to  Bundle 

Tricuspid  \/  ahe 

Right  Ventricle 

Chordce  Tendineas 


Papillary  Muscle 


FIG.  215. — HUMAN  HEART  OPENED  FROM  THE  RIGHT  TO  SHOW  THE  ATRIOVEN- 
TRICULAR BUNDLE  OF  His. 

The  illustration  shows  also  a  heart  valve,  the  chordae  tendinese,  and  the  pap- 
illary muscles.     (After  Curran,  Anat.  Rec.,  3,  12,  1909.) 


tricular  valves.  Either  of  the  last  two  forms  may,  in  transections  of  the 
ventricles,  appear  as  isolated  islands  of  muscular  tissue  surrounded  by 
endocardium  and  lying  apparently  free  within  the  cavity  of  the  ventricle. 
Columnar  carnese  which  span  the  ventricular  cavity  constitute  moderator 
bands.  One  such  band  is  frequently  present  in  the  right  ventricle  near  the 
apex,  and  occasionally  one  appears  in  the  left  ventricle. 

Atrioventricular  Bundle. — The  atrioventricular  bundle  of  His  was 
discovered  in  the  human  heart  by  His,  Jr.,  in  1893.  Previously  in  the 
same  year  it  had  been  noted  by  Kent  in  the  heart  of  a  number  of  mam- 
mals. It  has  since  been  seen  in  every  species  of  mammal  investigated, 


200 


THE  BLOOD  VASCULAR  SYSTEM 


It  consists  of  a  dense  meshwork  of  cardiac  muscle  fibers  rich  in  sarco- 
plasm,  in  the  form  of  a  band  taking  origin  in  scattered  fibrils  in  the 
posterior  wall  of  the  right  atrium  near  the  septum  in  the  atriovcutricular 
groove  (sinus  region;  hence,  sinoventricular  conducting  system,  Retzer, 
1908),  and  coursing  forward  in  the  interatrial  septum  into  the  upper 
anterior  portion  of  the  interventricular  septum,  where  it  divides  into  two 
limbs  which  branch  profusely  and  spread  out  in  a  complicated  system 

of  terminal  branches,  the 
subendocardial  Purkinje 
fibers.  Macroscopic-ally 
the  bundle  has  a  grayish 
appearance ;  where  it 
passes  from  the  intera- 
trial to  the  interventricu- 
lar septum  (pars  mem- 
branacea  septi)  it  ex- 
pands into  the  so-called 
node.  In  man  the  right 
limb  is  much  smaller 
than  the  left. 

The  bundle  of  the 
calf's  heart  has  been  re- 
constructed by  De  Witt 
(Anat.  Rec.,  3,  9,  1909). 
Curran  (Anat.  Eec.,  3, 
12,  1909)  has  described 
a  constant  bursa  or  lubri- 
(De  Witt,  Anat.  Rec.,  3,  9,  1909.)  eating  mechanism  in  re- 

lation with  the   bundle, 

furnishing  protection  against  friction  during  contraction  of  the  heart. 
He  describes  "its  connection  with  all  parts  of  both  auricles  through  three 
large  trunks  and  a  number  of  smaller  twigs,  and  not,  as  was  once 
thought,  merely  arising  in  the  right  auricle  only." 

Tawara  (1906)  first  carefully  described  the  histology  of  this  bun- 
dle in  several  mammals,  including  man.  De  Witt  more  recently  (1909) 
has  extended  the  study  in  this  same  field.  "In  the  sheep  and  calf,  where 
the  fibers  are  most  typical  and  most  clearly  differentiated  from  the 
myocardial  fibers,  the  fibers  are  much  larger  than  the  myocardial  fibers, 
with  fewer  fibrils  and  much  more  sarcoplasm."  She  describes  the  bundle 
as  a  muscular  syncytium.  "Connective  tissue  and  especially  elastic  fibers 


FIG.  216. — RECONSTRUCTION  OP  THE  SINOVEN- 
TRICULAR .SYSTEM  (BUNDLE  OF  His)  OF  THE 
CALF'S  HEART. 


HEART  201 

are  much  more  abundant  than  in  the  myocardium."  The  bundle  con- 
tains abundant  ganglion  cells  and  nerve  fibers.  It  is  also  very  rich  in 
glycogen.  In  the  ox  it  is  distinctly  cellular  (Fig.  112). 

It  would  seem,  on  the  basis  of  its  constancy  of  presence  and  structure, 
and  its  probably  independent  blood  and  nerve  supply,  that  the  atrioventric- 
ular  bundle  has  a  function  independent  of  the  myocardium,  probably  of 
the  nature  of  a  neuromuscular  end-organ  (Retzer;  DeWitt),  providing  for 
the  conduction  of  the  impulse  to  contraction,  and  the  coordination  of  the 
atrial  and  ventricular  rhythm. 

A  muscle  bundle  of  closely  similar  structure  intimately  related  with 
the  vagus  and  sympathetic  nerves,  the  'sino-atrial  node,'  has  been  described 
by  Keith  and  Flack  (1907)  at  the  juncture  of  the  sinus  venosus  and  the 
atrium.  It  is  believed  to  be  the  place  of  origin  of  the  impulse  to  the  heart 
beat,  from  which  it  is  transmitted  to  the  atrioventricular  bundle. 

Laurens  (Anat.  Rec.,  2,  8,  1913)  has  described  an  analogous  muscular 
connection  between  auricles  and  ventricles  in  certain  reptiles,  where  it 
assumes  the  form  of  an  inverted  funnel-shaped  tube. 

Development  of  Heart. — The  anlage  of  the  heart  arises  from  the 
fusion  of  a  pair  of  parallel  endothelial  tubes  in  the  paramedial  angioblast, 
each  surrounded  by  primitive  mesenchyma.  The  endothelium  of  the  result- 
ing sac  differentiates  into  the  endocardium  of  the  definitive  heart,  while 
the  connective  tissue  and  muscle  develop  from  the  mesenchyma  in  a  man- 
ner essentially  similar  to  that  described  for  the  blood-vessels. 

Blood- Vessels. — The  heart  is  supplied  with  blood  through  the  coro- 
nary arteries.  The  larger  branches  of  these  vessels  pursue  their  course 
beneath  the  epicardium  in  the  superficial  grooves  of  the  cardiac  wall. 
From  these  large  arteries,  smaller  branches  are  distributed  to  the  epi- 
cardium and  to  the  muscular  wall,  the  latter  vessels  penetrating  as  far 
as  the  endocardium,  in  whose  connective  tissue  they  form  a  meager 
capillary  plexus. 

The  capillaries  of  the  myocardium  are  extremely  abundant.  They 
form  elongated  meshes  between  the  muscle  fibers,  the  circumference  of 
each  muscle  fiber  being  in  "relation  with  several  capillary  vessels.  The 
veins  return  the  blood  from  these  rich  capillary  plexuses  and  pursue  a 
course  similar  to  that  of  the  arteries,  the  larger  veins  being  always  found 
in  the  broader  connective  tissue  septa.  In  the  right  atrium  certain  small 
veins,  the  vence  minima,  empty  directly  into  the  cavity  of  the  heart. 

The  lymph  supply  is  very  abundant  and  intimate.    The  lymph  ves- 
sels form  two  superficial  plexuses,  the  endocardial  and  the  epicardial, 
both  draining  into  the  larger  lymph  vessels  at  the  base  of  the  heart. 
14 


202  THE  BLOOD  VASCULAR  SYSTEM 

Nerve  Supply. — The  nerve  supply  of  the  vascular  system  is  hy  means 
of  fine  branches  from  the  cerebrospinal  and  sympathetic  systems.  In  the 
heart  these  minute  nerve  trunks  end  in  the  various  cardiac  ganglia, 
most  of  which  are  found  in  the  connective  tissue  of  the  heart,  e.g.,  the 
coronal  plexuses  about  the  orifices  of  the  aorta  and  pulmonary  artery. 
From  these  ganglia  sensory  nerve  fibers  are  distributed  to  the  endocar- 
dium and  epicardium,  and  motor  fibers  to  the  myocardium.  The  most  of 
the  former  are  connected  with  the  vagus,  the  latter  with  the  sympathetic 
trunks.  Through  both  the  vagus  and  the  sympathetic  trunks  are  dis- 
tributed also  efferent  cerebrospinal  fibers:  the  accessory  nerve  through 
the  vagus  contributes  'inhibitory'  fibers,  the  cervical  spinal  nerves  through 
the  inferior  cervical  ganglia  contribute  'accelerator/  fibers. 

From  the  cardiac  ganglia  branches  pass  to  form  a  coarse  plexus  in 
the  connective  tissue  between  the  muscle  bundles,  the  perimysial  plexus, 
from  the  branches  of  which  a  fine  plexus  is  distributed  to  the  endo- 
mysium.  The  terminal  branches  end  in  relation  with  the  surface  of  the 
muscle,  fibers. 

The  pericardium  contains  numerous  encapsulated  nerve  endings 
(corpuscles  of  Golgi  and  Mazzoni).  According  to  Martynoff  (Arch, 
mikr.  Anat.,  vol.  84,  191-i)  unencapsulated  endings  also  are  present,  of 
three  types :  coils,  dendriform  terminal  ramifications,  and  modified  den- 
driform endings.  He  describes  also  naked  terminal  filaments  ending  on 
the  bases  of  the  mesothelial  covering  cells. 

The  blood-vessels  are  similarly  supplied,  minute  ganglia  occurring 
here  and  there  in  the  adventitia  or  adjacent  connective  tissue?  From 
these  ganglia  sensory  branches  are  distributed  to  the  adventitia  and  in- 
tima  and  motor  branches  to  the  tunica  media.  Xaked  nerve  fibrils  can  be 
traced  to  the  smallest  blood-vessels,  and  even  in  the  capillaries  terminal 
fibrilla?  are  found  in  relation  with  the  endothelial  wall. 


CHAPTER   VIII 
BLOOD 

Blood  may  be  regarded  as  a  tissue  in  which  the  intercellular  material 
is  a  fluid,  the  plasma.  The  plasma  contains  fibrin  in  solution  (fibrino- 
gen) ;  on  exposure  to  air,  as  in  case  of  cuts,  the  fibrin  is  precipitated  in 
the  form  of  delicate  needle-like  crystals  (Fig.  217),  leaving  a  clear  straw- 
colored  liquid,  the  serum.  The  active  element  in  causing  this  precipita- 
tion is  thrombin  (or  prothrombin),  probably  liberated  by  the  blood- 
platelets  on  disintegration  under  the  influence  of  air  or  the  stimulus 
of  a  roughened  area  on  the  wall  of  the  blood-vessels.  The  blood-cells 
become  entangled  in  this  fibrin  net  forming  a  clot  or  thrombus.  Plasma 
is  very  similar  to,  but  not  identical  with,  the  lymph  of  the  lymph 
vessels. 

The  formed  elements,  or  blood-cells,  are  of  two  main  classes,  red 
and  white,  or  erytliroplastids  (erythrocytes)  and  leukocytes.  The  red 
blood  corpuscles  or  plastids  owe  their  characteristic  color  to  the  presence 
of  hemoglobin.  Single  corpuscles  have  a  light  yellowish-green  color,  in 
masses  they  appear  red.  The  function  of  the  hemoglobin  is  to  carry 
oxygen  in  weak  combination  as  oxyhemoglobin  for  transportation  through 
the  blood-vessels  from  the  lungs  to  the  tissues,  where  it  is  employed  in 
the  oxidation  processes  upon  which  life  depends. 


THE  RED  BLOOD  CELL 

The  erythroplastid  is  a  circular  biconcave  disk,  of  7.5  microns  (a 
micron  is  1-1000  of  a  millimeter)  diameter.  They  are  present  in  prac- 
tically all  histologic  preparations,  hence  they  serve  well  as  a  ready 
scale  for  approximate  determination  of  size  of  cellular  elements  in  the 
same  microscopic  field.  Every  section;  blood  preparation,  as  of  a  drop 
under  a  cover-slip;  and  even  the  blood-vessels  of  living  mammals,  con- 
tain also  a  larger  or  smaller  number  of  cells  of  saucer  shape  (cup  shape; 

203 


204  BLOOD 

bell  shape,  etc.)-    These  are  believed  by  some  (Weidenreich,  Lewis,  Mi- 
not,  and  others)  to  be  the  more  normal  in.  shape ;  however,  there  remains 


FIG.  217. — OXALATED  PLASMA  OF  HUMAN  BLOOD  CLOTTED  WITH  THROMBIN, 
SHOWING  FIBRIN  NEEDLES.     X  512. 

(After  Howell,  Amer.  Jour.  Physiol.,  35,  1,  1914.) 


little  doubt  that  the  circular  biconcave  disk  shape  is  the  normal  (origi- 
nal), the  saucer  or  cup  shapes,  the  derived  forms,  the  result  of  modifi- 


THE  BED  BLOOD  CELL 


205 


cation  by  extrinsic  factors.  The  erythroplastid  is  of  course  a  very 
delicate  structure,  and  slight  tractions  or  tensions  incident  to  passage 
through  exiguous  confines,  or  osmotic  currents  set  up  in  fixing  fluids, 
or  the  coagulation  of  its  protoplasm,  would  produce  modifications  and 
distortions.  Almost  any  conceivable  mechanical  modification  would  of 


FIG.  218. — FROM  A  FRESHLY  PREPARED,  UNSTAINED  SPECIMEN  o*^  HUMAN  BLOOD. 

Three  leukocytes,  an  eosinophil,  a  polynuclear,  and  a  lymphocyte,  are  represented. 
Many  red  blood  corpuscles  (erythroplastids),  some  on  the  flat,  some  in  rouleaux 
and  in  profile,  are  also  shown.  X  1200,  but  reduced  somewhat  in  reproduction. 
(After  Schafer.) 


necessity  change  a  circular  biconcave  disk  into  some  sort  of  cup-shaped 
element. 

The  red  blood  element  lacks  a  nucleus,  hence  the  propriety  of  in- 
sistence on  the  term  'plastid'  or  'corpuscle'  in  preference  to  cell  (cyte). 
The  red  elements  of  all  mammals  are  non-nucleated.  The  lower  forms 
have  nucleated  elements  (cryllirocytes),  frequently  of  ellipsoidal  form. 
Mammalian  red  elements  of  greatly  divergent  sizes  (2.5  /*  in  musk  ox; 
9.4/1  in  elephant;  dog,  7.5 /t  )  are  all  of  circular  outline,  except  those 
of  the  camel  idaj  (llama,  camel,  etc.)  which  are  elliptical.  The  erythro- 
plastids  are  generally  believed  to  be  enclosed  by  a  delicate  membrane,  and 


206 


BLOOD 


to  contain  a  very  delicate  stroma  (spongioplasm)  and  fluid  matrix  (hyal- 
oplasm, with  hemoglobin).  The  red  corpuscles  have  a  tendency  when  ex- 
posed, as  in  a  drop  mounted  under  a  cover-slip,  to  arrange  themselves  in 
rows,  like  coins  in  a  pile,  concave  surfaces  apposed,  forming  rouleaux. 
Drop  preparations  show  after  a  short  time  also  an  increasing  number  of 
plastids  with  puckered  or  spiny  surfaces,  crenated  corpuscles.  This  condi- 
tion results  from  evaporation  producing  a  medium  of  greater  density  than 
that  of  the  normal  blood  plasma.  Any  me- 
dium of  density  equal  to  that  of  the  plasma 
of  any  particular  blood  is  spoken  of  as  an 
isotonic  solution  for  that  blood.  The  solu- 
tion in  most  common  use  for  human  blood 
is  a  0.9  per  cent,  solution  of  sodium  chlorid 
in  distilled  water.  Solutions  of  higher  den- 
sity are  hypertonic;  these  produce  exosmotic 
currents  causing  destruction  leading  through 
crenation.  Solutions  of  lower  density,  for 
example,  water,  are  liypotonic;  they  produce 
destruction  (hemolysis)  through  endosmosis 
causing  swelling,  a  stage  of  which  shows  a 
saucer-shaped  corpuscle.  This  is  accom- 
panied by  laking,  or  extraction  of  hemoglo- 
bin, giving  rise  to  a  &  ^  d  g 
blood  shadows;  and  f)  &  £k  f\  /^\ 
final  bursting,  leav-  B  9  9  **  ^ 
ing  a  debris  called  FIG.  220.  —  SHOWING  THE 

hemokonia.  AcTI°*  OF  ^ATER  Yf°N 

,  THE    RED    BLOOD    COR- 

The  number  of  PUSCLE. 
red    corpuscles 


FIG.  219.  —  BLOOD  CELLS 
FROM  A  SPECIMEN  OP 
FRESHLY  DRAWN  UN- 
STAINED HUMAN  BLOOD. 

A,  red  blood  corpuscles, 
deep  focus,  showing  a  light 
center  and  dim  margin;  B, 
the  same  with  a  higher  focus; 
the  center,  being  slightly  out 
of  focus,  is  dim  while  the 
margin  is  light;  C,  crenated 
red  corpuscles  from  the  mar- 
gin of  the  preparation;  a, 
deep  focus;  b,  higher  focus; 
D,  two  polymorphonuclear 
leukocytes;  E,  large  mono- 
nuclear  leukocyte.  X  750. 


a,  the  corpuscle   in  pro- 


the  blood  is  subject  file;    b-e,  various  stages  in 

to    constant    varia-  the    transformation    which 

,.         ,    ,                 .  n  leaves  only  a    shadow     e; 

tion   between  wide  diagranfmatic.    (After 

limits.        Many   Schafer.) 

physiologic  condi- 
tions influence  their  total  number,  as  well  as  the  relative  proportion  of 
red  elements  to  the  white.  The  average  number  of  red  corpuscles  in  the 
adult  male  is  about  5,000,000  per  cubic  millimeter.  In  young  robust 
persons  the  number  may  be  considerably  higher.  The  number  may  also 
be  much  reduced  by  considerable  hemorrhages  or  by  the  imbibition 
of  large  quantities  of  fluid.  Profuse  perspiration  tends  to  produce 


THE  WHITE  BLOOU  CELLS  207 

concentration  of  the  blood  and   an   apparent   increase  in   the   number 
of  its  corpuscles.     The  number  of  red  blood  corpuscles  in  the  female 


£b 


FIG.  222. — THREE  NU- 
CLEATED RED  BLOOD 
CELLS  (ERYTHRO- 

CYTES)      FROM      THE 

FIG.  221. — FIVE  NUCLEATED  RED  CELLS  MARROW  OF  A  Hu- 

(ERYTHROCYTES)  FROM  THE  BLOOD  OF  MAN  RJB. 

A  FROG. 

Eosin    -    methylene 

Eosin-methylene      blue.        Hasting's  blue.     Nocht  method, 

method.     X  1200.  X   1200. 

is  slightly  less  than  in  the  male,  about  4,500,000  per  cubic  millimeter. 
The  average  life  of  an  erythroplastid  is  approximatety  30  days  (Ashby; 
Journ.  Exp.  Med.,  vol.  29,  1918). 

THE  WHITE  BLOOD  CELLS 

Under  leukocytes  are  grouped  the  following  types:  (1)  lymphocytes; 
(2)  non-granular  or  mononuclear  leukocytes  and  (3)  granular  leukocytes 
— granulocytes.  These  are  all  nucleated  elements.  Leukocytes  lack  a 
cell  membrane;  all  are  phagocytic,  especially  the  neutrophils;  they  aver- 
age about  8,000  to  a  cubic  millimeter  of  blood. 

Lymphocytes. — The  lymphocytes  are  perhaps  the  least  differentiated 
blood  element.  They  are  of  two  main  varieties,  large  and  small,  between 
which  are  intergrades.  The  small  lymphocyte  is  about  the  size  of  an 
erythroplastid ;  its  nucleus  is  a  dense,  deeply  chromatic  spheroidal  body ; 
it  has  a  very  thin  shell  of  very  finely  granular  or  non-granular  faintly 
basophilic  cytoplasm.  The  large  lymphocyte  (12  to  15  /*  )  differs  from 
the  small,  both  in  somewhat  larger  size  of  nucleus  and  slightly  wider 
shell  of  cytoplasm.  The  simplest  and  more  than  likely  the  correct  con- 
ception of  the  relationship  of  large  to  small  lymphocytes  is  one  of  growth ; 
that  is,  a  large  lymphocyte  is  a  fully  grown  small  lymphocyte,  a  small 
lymphocyte  is  a  daughter-cell  of  a  large  lymphocyte.  They  constitute 
about  20  per  cent,  of  the  total  white  blood  cell  content.  They  are  the 


208 


BLOOD 


almost  exclusive  cell  type  of  lymph.  They  take  origin  in  the  adult  in 
lymph  organs,  spleen  and  bone-marrow.  In  infancy  their  proportion  is 
much  greater,  about  50  per  cent. ;  this  increase  is  at  the  expense  of  the 
neutrophil  granulocytes. 

Non-granular  Leukocytes.— These  are  characterized  by  a  large,  fre- 
quently bean-shaped  vesicular   (clear,  pale)   nucleus,  and  an  extensive 


FIG.  223. — A  GROUP  OF  CELLS  FROM  NORMAL  HUMAN  BLOOD. 
/,  red  blood  corpuscles  in  rouleau  formation;  2,  red  blood  corpuscles,  surface 
view;   3,    lymphocyte;   4,    large   mononuclear    leukocyte;   5,    polymorphonuclear, 
finely  granular  leukocyte;  6,  eosinophil  leukocyte;  7,  a  group  of  blood  platelets;  8, 
basophil  leukocyte.     Eosin-methylene  blue.     Basting's  method.     X  1200. 


shell  of  homogeneous  faintly  basophil  cytoplasm.  They  constitute  from 
2  to  4  per  cent,  of  the  white  cell  total;  they  are  notably  phagocytic. 
Occasionally  a  few  larger  neutrophilic  cytoplasmic  granules  may  be 
present.  Morphologically,  both  from  the  viewpoint  of  nucleus  and  cyto- 
plasm, they  are  transitional  between  lymphocytes  and  granulocytes, 
hence  the  use  of  transitional  leukocyte  as  synonym  for  non -granular 
or  large  mononuclear  leukocytes.  Modification  of  this  cell,  characterized 


THE  WHITE  BONE  CELLS  209 

by  great  increase  of  nuclear  and  cytoplasmic  constituents,  gives  rise  to 
the  so-called  GIANT  CELLS.  These  are  of  two  sorts,  depending  upon 
whether  the  nucleus  is  single  or  multiple,  the  megakaryocyte  and  the 
polykaryocyte.  The  latter  represents  a  modification  of  the  former,  and 
must  not  be  confused  with  the  osteoclasts  of  developing  bone. 

Megakaryocytes  are  practically  limited  to  bone-marrow.  They  fre- 
quently show  long  and  numerous  pseudopodia.  These,  as  also  the  cell- 
body  proper,  show  a  differentiation  of  the  cytoplasm  into  a  superficial 
hyaline  layer  and  a  central  basophilic  granular  core.  According  to 
Wright,  constriction  and  segmentation  of  these 
pseudopods  give  rise  to  the  BLOOD-PLATELETS 
(plates ;  plaques) .  These  commonly  hold  positions 
at  the  center  of  masses  of  converging  fibrin  fibrils 
in  blood  clots,  in  consequence  of  which  they  are 


supposed  to  be  the  essential  elements,  probably     FIG.  224. — GROUP  OP 
liberating    'thrombin',    in    clotting,    hence    their     Two^LAlaE^BLo™ 
synonym,  thrombocyte.    This  term,  however,  is  ill-     PLATELETS.    X2000. 
chosen,   for   these  elements   contain   no   nucleus. 

What  simulates  a  nucleus  is  the  central  spheroidal  mass  of  basophilic 
granules.  Blood-platelets  are  capable  of  ameboid  motility.  They  vary 
in  diameter  from  2  to  4  microns,  and  in  number  per  cubic  millimeter 
from  200,000  to  800,000.  Analogous  elements  of  avian,  reptilian  and 
ichthyoid  bloods  are  nucleated  spindle  cells,  or  true  thrombocytes. 
Wright's  observations  on  mammalian  megakaryocytes  furnish  at  present 
the  best  data  for  the  genetic  interpretation  of  blood-platelets.  How- 
ever, almost  every  conceivable  mode  of  origin,  notably  from  extruded 
nuclei  of  erythrocytes,  and  fragmenting  leukocytes  have  had,  and  still 
claim,  prominent  supporters. 

Granulocytes.. — The  granulocytes  comprise  three  varieties  distin- 
guished on  the  basis  of  their  cytoplasmic  granules:  (1)  neutrophils;  (2) 
eosinophils  (oxyphils)  and  (3)  basophils,  or  mast  leukocytes.  The  nu- 
cleus is  of  the  polymorph  type,  perhaps  occasionally,  polynuclear.  This 
nuclear  condition  consists  in  a  commonly  crescentic  chain  of  nuclear 
masses,  connected  by  frequently  extremely  delicate  nuclear  strands. 

The  NEUTROPHILS  are  characterized  by  their  fine  cytoplasmic  gran- 
ules, having  a  neutrophil  staining  reaction  (lilac  color)  in  mixtures  of 
acid  (eosin)  and  basic  (methylene  blue)  dyes.  They  range  in  size 
from  7.5  /t  to  10  p.  in  diameter.  They  are  predominantly  phagocytic. 
They  constitute  in  normal  adult  life  about  70  per  cent,  of  the  total  white- 
cell  blood  content. 


210  BLOOD 

The  EOSIXOPIIILS  contain  larger  spheroidal  cytoplasmic  granules 
which  show  a  special  affinity  for  eosin.  They  are  slightly  larger  than  the 
neutrophilic  granulocytes,  and  comprise  about  4  per  cent,  of  the  leuko- 
cytes of  normal  blood. 

The  BASOPHILS  are  characterized  by  an  extremely  variable  polymor- 
phous nucleus,  but  especially  by  their  spheroidal  and  irregular  basophilic 
granules  of  greatly  varying  sizes.  They  occur  to  the  extent  of  only  about 
0.5  per  cent,  in  the  circulating  blood.  They  are  of  approximately  the 
same  size  as  the  eosinophils.  Their  significance  and  genetic  relationship 
is  uncertain,  but  they  are  usually  interpreted  as  degenerating  granulo- 
cytes, the  granules  being  variously  regarded  as  products  of  nuclear  frag- 
mentation, and  as  cytoplasmic  products  of  mucoid  degeneration.  Maxi- 
mow  (Arch.  mikr.  Anat.,  83,  1,  1913),  however,  regards  the  'mast  cells' 
of  the  blood  as  specialized  kinds  of  granulocytes,  distinct  from  similar 
cells  of  the  tissues,  and  without  sign  of  degeneration. 

Cowdry  has  demonstrated  mitochondria,  by  vital  staining  with  janus 
green,  in  all  types  of  leukocytes,  except  mast  leukocytes,  including  plate- 
lets. The  lymphocytes  and  polymorph  neutrophils  contain  them  abun- 
dantly. They  are  only  sparsely  present  in  eosinophils.  Mitochondria  are 
said  to  be  totally  absent  in  the  erythroplastids  of  normal  adult  human 
blood  (Intern.  Monatschr.  Anat.  u.  Physiol.,  31,  4,  1914). 

P.  Ehrlich  in  a  series  of  communications  announced  that  by  coloring 
the  leukocytes  with  various  stains  he  was  able  to  distinguish  by  their 
reaction,  several  types  of  granules.  These  he  called  (  a  )  oxyphil  or  acido- 
pbil,  which  were  deeply  stained  by  eosin,  acid  fuchsin,  etc.;  (/?)  amphophil, 
which  were  stained  both  by  eosin,  and  by  dahlia  and  like  dyes ;  (  y )  baso- 
phil,  which  were  stained  deeply  by  dahlia,  thionin,  etc.;  (8)  certain  cells 
which  neither  after  staining  with  eosin,  etc.,  nor  with  dahlia,  etc.,  could 
be  made  to  show  any  granules  other  than  the  nodes  of  cytoreticulum ;  (  e  ) 
neutrophil,  which  can  be  stained  only  by  a  due  admixture  of  acid  and  basic 
dyes,  as  of  fuchsin  and  methylene  blue,  or  the  so-called  'triacid  mixture;' 
of  Ehrlich. 

The  demonstration  of  these  characteristics  presupposed  a  division  of 
dyes  'nto  three  primary  classes: 

1.  Acid — e.g.,  eosin,  orange-G,  acid  fuchsin,  aurnntia,  crythrosin. 

2.  Basic — e.g.,  methylene  blue,  dahlia,  thionin,  hematiii. 

3.  Neutral — which  are  only  formed  by  the  interreaction  of  ex- 

amples of  each  of  the  two  preceding  classes ;  the  neutral  dye 
is  supposed  to  arise  de  novo  in  such  mixtures,  as  a  result  of 
chemical  reaction. 


HEMOGLOBIN 


211 


The  application  of  such  a  classification  of  stains  to  other  tissues  than 
the  blood  has,  however,  been  found  to  present  considerable  difficulties. 

According  to  Kite  the  cytoplasm  of  the  polymorphonuclear  leukocytes 
has  nothing  of  the  nature  of  a  cell  membrane,  but  they  are  completely 
naked,  nor  do  they  contain  a  spongioplasm  and  hyaloplasm.  "The  cyto- 
plasm is  a  jelly  in  which  are  embedded  large  numbers  of  globules."  The 
structures  usually  termed 
cytoplasmic  granules  are  of 
the  nature  of  separation 
products ;  they  do  not  grade 
into  the  surrounding  cyto- 
plasm. All  leukocytes  un- 
dergo also  certain  definite 
structural  transformations, 
characterized  by  the  appear- 
ance of  pseudopods  chang- 
ing into  vibratile  cilia.  Kite 
suggests  that  the  protoplas- 
mic processes  may  be  prom- 
inently concerned  in  phago- 
cytosis. Under  certain  con- 
ditions erythroplastids  may  FlG.  225.— OUTLINE  DRAWINGS  OF  LIVING  POLY- 
be  made  to  protrude  similar  MORPHONUCLEAR  LEUKOCYTES  OF  RABBIT, 
processes  (Jour.  Infect.  ™OM  A  DKOP  OF  BLOOD  M1XED  WI™  RlNGER's 

*  01      \  (SOLUTION    TO     WHICH    A    OMALL    AMOUNT    OF 

Uis.,  15,  2,  1J14).  HIRUDIN  HAD  BEEN  ADDED  TO  PREVENT  COAG- 

ULATION. 

HEMOGLOBIN  In  *he  course  of  half  an  hour  the  cells  develop 

retractile  undulatory  processes,     a,  hyaline-sur- 

Hemoo-lobin    is    a    very      face  phase;  x>  hyaline  lfiyer>  b  and  c>  ciliated 
J       phase;  d,  flagellated  phase.     Leukocytes  of  all 

complex  chemical  compound      classes  of  vertebrates  undergo  similar  changes, 
of  iron  with  a  globulin;  it       (After    Kite,    Jour.     Infectious    Dis.,     15,    2, 
gives  the  characteristic  color 
to  the  blood.     It  combines 

readily  with  oxygen  to  form  oxyhemoglobin,  a  loose  chemical  combina- 
tion by  which  the  oxygen  is  carried  from  the  lungs  to  the  tissues,  and 
which  gives  the  brighter  red  color  to  the  arterial  as  compared  with  the 
venous  blood.  The  hemoglobin  is  held  either  in  solution  or  in  unstable 
chemical  union  by  the  cytoplasm  of  the  erythroplastids.  It  escapes  from 
these  corpuscles  after  rupture,  or  it  may  be  extracted  by  ether,  and  is 


212 


BLOOD 


then  prone  to  crystallize  on  evaporation  in. the  form  of  minute  brownish- 
yellow  prisms.  The  crystals  of  the  various  species  of  any  genus  belong 
to  a  crystallographic  group  (Reichert)  but  generic  differences  are  fre- 
quently striking;  thus,  in  human  blood  they  are  long  rhombohedra  (Fig. 
227),  in  guinea  pig,  tetrahedra,  in  squirrel,  hexagonal  plates,  in  rat, 


FIG.  226. — SECTION  OP  BONE  MARROW  FROM  SKULL  OF  25  MM.  TURTLE  EMBRYO 
(CHELYDRA  SERPENTINA),  SHOWING  THREE  MAIN  STAGES  IN  THE  HEMOPOIESIS. 

L,  hemoblast  (lymphocyte),  differentiating  in  the  mesenchyma  and  passing  into 
a  blood-vessel;  Me,  blood  mother  cell  (hemoblast);  Mg,  megaloblast;  Eb,  erythro- 
blast;  EC,  erythrocyte;  E,  endothelial  cell;  Mes,  mesenchymal  cell;  PC,  pigmented 
cell.  Helly  fixation;  Giemsa  stain.  X  700. 

elongated  six-sided  plates,  in  hamster  (a  rodent),  rhombohedra,  and  in 
dog  they  appear  as  rhombic  prisms  which  are  diamond  shaped  in  cross- 
section. 

Various  other  crystalline,  and  also  amorphous  hemoglobin  derivatives 
may  occur  as  decomposition  products.  The  iron  of  the  coloring  matter 
of  the  hemoglobin  may  be  thus  obtained  in  the  form  of  hematin,  a 
soluble,  amorphous  protein  compound  of  a  brownish-red  color.  If  he- 
matin  is  combined  with  hydrochloric  acid  the  chlorid  of  hematin,  hemin, 
is  produced.  Hemin  occurs  in  deep  brownish-red  crystals,  known  also  as 
Teichmann's  crystals,  which  differ  somewhat  according  to  the  animal 


HEMOGLOBIN 


213 


species  from  which  they  are  obtained;  those  of  human  blood  take  the 
form  of  triclinic  plates  .(Fig.  228).  Hemin  crystals  derive  a  certain 
importance  as  a  forensic  test  for  the  presence  of  blood,  and  they  may 
be  obtained  from,  old  and  dried-up  specimens  as  readily  as  from  fresh 
blood.  The  procedure  for  testing  a  suspected  stain  consists  in  heating 

to  the  boiling  point  in  a  drop 
of  acetic  acid,  a  drop  of  a  nor- 
mal salt  solution  of  the  speci- 
men. From  fresh  blood  the 
crystals  may  be  produced  by 
heating  together  on  a  slide  a 
drop  of  blood,  a  grain  of  so- 
dium chlorid,  and  a  drop  of 
acetic  acid.  Hemin  crystals 
prove  only  that  hemoglobin  is 
present,  but  give  no  precise  in- 


FIG.  227. — HEMOGLOBIN  CRYSTALS. 

a  and  b,  from  human  blood;  c,  from  the  cat; 
rl,  from  the  guinea-pig;  e,  from  the  hamster;  /, 
from  the  squirrel.  (After  Ranvier.) 


FIG.  228.  —  CRYSTALS  OF 
CHLORID  OF  HEMATIN  OR 
HEMIN. 

(After  Ranvier.) 


formation  as  to  the  species  from  which  the  blood  in  question  came,  for 
the  crystals  obtained  from  many  mammals  are  apparently  identical. 

Hematin  may  decompose  also  into  hemosiderin,  an  iron-containing 
hemoglobin  derivative,  in  the  form  of  light-brown  granules,  frequently 
found  in  phagocytic  leukocytes  as  the  product  of  cellular  digestion  of 
effete  erythroplastids.  Hemosiderin  granules  thus  appear  in  the  spleen 
and  bone-marrow.  Iron  in  the  tissues,  and  ferruginous  pigments  gen- 
erally, can  be  recognized  by  application  of  the  ferrocyanid  test,  which 
stains  the  iron  blue. 


214  BLOOD 

When  extravasations  of  blood  occur  within  the  tissues  of  the  body, 
as,  for  example,  in  the  corpus  hemorrhagicum  of  the  ovary,  the  hematiu 
is  frequently  deposited  as  he-mat  oiditi,  an  iron-free  derivative  of  hemo- 
globin which  forms  stellate  groups  of  yellowish  needle-like  crystals.  He- 
matoidin is  apparently  identical  with  bilirubin,  a  bile  pigment. 


COAGULATION 

According  to  Howell's  theory  of  coagulation,  prothrombin,  probably 
produced  at  least  in  part  by  disintegrating  platelets,  in  the  presence  of 
calcium  is  converted  into  thrombin.  The  latter  precipitates  from  the 
fibrinogen  of  the  blood  plasma  the  fibrin  needles  which  mass  to  produce 
a  mesh  in  which  the  corpuscles  become  aggregated  to  form  the  thrombus 
or  clot.  Howell  has  recently  studied  with  the  ultramicroscope  the  process 
of  coagulation  in  oxalated  blood  plasma  and  solutions  of  fibrinogen  to 
which  a  solution  of  thrombin  was  added.  He  describes  clotting  as  pro- 
ceeding after  the  manner  of  crystal  formation;  the  crystals  begin  as 
granules  which  adhere  to  form  threads.  Clotting  is  'an  aggregation  of 
the  invisible  particles  (amicrons)  to  visible  particles  and  then  the  further 
consolidation  of  these  particles  into  rigid  looking  needles'  (Amer.  Jour. 
Physiol.,  35,  1,  1914). 

HEMOPOIESIS 

A  consideration  of  blood  development  involves  the  questions  of  the 
sources  of  primary  origin  and  the  genetic  relationship  of  the  different 
varieties  of  cells.  The  blood-forming  or  hemopoietic  organs  comprise  (1) 
the  yolk-sac;  (2)  body  mesenchyme  and  endothelium  of  primitive  blood- 
vessels of  the  embryo;  (3)  liver  and  spleen;  assisted  by  lymph  organs  in 
the  production  of  lymphocytes,  and  finally  (4)  marrow  of  fetal  and  adult 
bone.  These  several  sources  function  in  development  in  the  order  enumer- 
ated, though  the  successive  stages  overlap  to  some  extent.  With  the 
assumption  of  function  on  the  part  of  bone-marrow — the  earliest  foci  being 
the  scapular,  pelvic,  vertebral  and  costal  elements — the  other  blood-forming 
organs  cease  activity.  However,  in  certain  diseases  the  spleen  may  possibly 
be  stimulated  to  renewed  function;  and  lymph  organs  function  throughout 
life  in  the  production  of  lymphocytes.  From  the  standpoint  of  the  germ 
layers  hemapoiesis  is  more  probably  limited  to  the  mesoderm  (mesenchyme). 
This  is  certainly  true  largely  at  least,  probably  completely,  of  sources 
outside  of  the  yolk-sac. 


HEMOPOIESIS 


215 


The  yolk-sac  wall  is  the  earliest  locus  of  blood-cell  origin.  This  struc- 
ture is  a  vesicle  lined  by  columnar  entodermal  cells,  invested  by  mesen- 
chyme,  the  surface  cells  of  which  become  arranged  in  the  form  of  a  mem-. 
bra  no,  the  mesothelium.  The  first  anlage  of  blood  appears  in  the  shape 
of  irregular  masses  and  cords  of  cells  next  the  entoderm.  These  cords 
anastomose  at  the  same  time  that  they  acquire  lumina  through  a  process 
which  involves  the  peripheral 
differentiation  of  cells  into 
endothelium  and  the  appear- 
ance of  plasma  in  which  the 
central  cells  are  suspended. 
The  very  intimate  spatial  re- 
lationship of  these  blood- 
islands  to  the  entoderm  has 
led  many  to  incline  to  an  en- 
todermal origin  of  the  earliest 
blood  anlages.  The  layer  in 
which  blood  first  appears  in 
the  yolk-sac  has  been  named 
angioblast,  a  term  which  does 
not  commit  one  to  any  view 
as  to  primitive  germ  layer 
origin.  However,  the  impor- 
tance of  the  matter  of  origin 
seems  great  only  when  one 
believes  in  the  strict  specifi- 
city of  germ  layers.  Such 
position  is  hardly  tenable  in 
view  of  the  fact  that  origin- 
ally there  is  only  one  germ 
layer,  the  ectoderm,  and  the 
origin  of  the  mesoderm  from 

the  primitive  streak,  a  phase  of  fusion  of  ectoderm  and  entoderm.  More- 
over, in  certain  forms,  e.g.,  Tarsius,  a  primate,  it  is  claimed  by  Hubrecht 
that  mesoderm  has  a  double  origin  from  ectoderm  and  entoderm,  as  well  as 
from  primitive  streak.  Again  in  subsequent  early  embryonic  stages  it  is 
believed  by  many  that  blood-cells  arise  by  process  of  differentiation  of  body 
mesenchyme.  In  the  further  discussion  of  hemopoiesis  we  may  take  for 
granted  the  origin  of  blood  exclusively  from  mesenchymal  elements. 

Regarding  the  question  of  the  original  blood  mother-cell  two  sharply 
contrasting  views  are  held,  expressed  in  the  monophyletic  (unitarian)  and 
polyphyletic  (dualistic)  theories  of  blood-cell  origin.  The  former  holds 
that  all  types  of  blood  elements,  red  and  white,  have  their  origin  directly 
in  one  and  the  same  primordial  blood  cell  ('hemagonium,'  hemoblast) ;  the 


FIG.  229. — WALL  OF  YOLK-SAC  OP  A  13  MM. 
HUMAN  EMBRYO  (Fie.  210),  SHOWING  A 
SMALL  BLOOD  ISLAND  (B.  I.)  AND  SEVERAL 
SMALL  BLOOD  VESSELS  CONTAINING  ERY- 
THROCYTES. 

The  wall  consists  of  stratified  columnar  and 
cuboidal  entodermal  cells  (to  the  right),  a 
middle  mesenchymal  layer  (angioblast),  and  a 
covering  of  mesothelium. 


X  240. 


216  BLOOD 

several  types  are  conceived  to  arise  through  process  of  differentiation  along 
distinct  lines.  '  The  polyphyletic  theory  holds  to  a  dual  origin,  from  geneti- 
cally distinct  mother-cells,  for  red  and  white  cells;  or  to  a  multiple 
origin,  tracing  erythrocytes  and  the  several  varieties  of  leukocytes  each 
along  different  lines  of  differentiation  to  different  mother-cells.  The  later 
investigations  into  this  problem  of  blood-cell  origin — done  with  an  admit- 
tedly superior  technic — tend  to  show  that  the  monophyletic  view  is  correct. 
This  was  first  well  supported  by  the  work  of  Saxer,  who  gave  the  name 


l^f/itf 


pa. 

tf*    A^P'g^^iff 
IT 


FIG.  230.— LARGE  BLOOD  ISLAND  FROM  (Fio.  210),  A  13  MM.  HUMAN  EMBRYO. 

a1  and  a2,  mesenchymal  cells;  a1  is  differentiating  into  an  endothelial  cell;  a3,  endo- 
thelial  cells  becoming  separated  from  wall  to  form  hemoblasts  ('lymphocytes'); 
61  and  b2,  hemoblasts  (mesameboids) ;  c,  megaloblasts;  dl  and  d2,  normoblasts;  R, 
binucleated  giant  cell.  X  750. 

'primary  wandering  cell'  to  the  common  blood-mother  cell;  more  recently 
by  the  work  of  Maximow,  who  applies  the  name  'lymphocyte'  (primary 
lymphocyte)  to  this  cell,  on  the  ground  of  its  resemblance  to  the  large 
lymphocyte  of  adult  blood.  This  lymphocyte  (hemoblast)  is  according  to 
Maximow  originally  a  cell  of  the  general  mesenchyrna,  the  earliest  differen- 
tiation stages  of  which  are  characterized  by  increase  of  basophily  of  the 
cytoplasm,  separation  from  the  general  syncytium,  and  assumption  of 
ameboid  properties.  These  steps  involve  blood-island  stages. 

We  may  now  trace  the  steps  through  which  the  primitive  blood-cell 
passes  in  the  process  of  attaining  the  adult  condition  of  the  various  types 
of  cells.  Of  two  daughter-cells  one  differentiates  into  an  erythroblast ;  the 
other  may  remain  as  a  primitive  blood-cell  to  further  function  as  a  mother- 
cell;  at  the  same  time  primitive  blood-cells  may  continually  differentiate 
In  adult  life  from  the  mesenchyme  of  bone-marrow.  An  alternative  view 


BONE-MARROW  217 

accepted  by  some,  e.g.,  Miiiot, — and  still  in  accord  with  the  monophyletic 
teaching — regards  the  later  embryonic,  fetal  and  adult  hemopoietic  organs 
as  simply  foci  of  proliferation  and  differentiation  of  primordial  blood-cells 
(hemoblasts)  originally  derived  from  the  angioblast  and  subsequently 
carried  by  the  blood  stream  to  these  locations  (red  marrow,  etc.)  where  they 
persist  throughout  life. 

\Ve  will  follow  first  the  several  steps  in  the  developmental  process  of  the 
red  element,  to  which  taken  together  the  name  'erythrocyte'  may  be  appro- 
priately applied.  According  to  Maximow,  in  the  forms  studied  by  him, 
there  are  two  lines  of  erythrocytes,  a  primitive  and  a  definitive  line;  the 
primitive  line  dies  out  after  a  brief  span,  and,  since  the  definitive  line 
differs  only  in  the  matter  of  smaller  size  of  cells,  we  may  confine  our  atten- 
tion to  that  line. 

The  several  stages  in  the  differentiation  process  are:  (1)  megaloUast; 
(2)  normoblast;  (3)  erythrollast  and  (4)  erythroplastid  ('erythrocyte')- 
All  except  the  last  may  multiply  by  mitosis.  The  megaloblast  differs  from 
its  progenitor,  the  hemoblast,  in  having  somewhat  more  cytoplasm,  and  a 
small  amount  of  hemoglobin,  which  gives  it  a  light  reddish-brown  color. 
Its  nucleus  is  relatively  large  and  vesicular  and  contains  a  delicate  gran- 
ular network;  this  stage  corresponds  to  the  ichthyoid  stage  of  Minot;  a 
seemingly  appropriate  terminology,  since  it  calls  attention  to  the  similarity 
between  the  adult  (phylogeiietic)  stage  of  a  lower  form,  and  the  embryonic 
(ontogenetic)  stage  of  a  higher  form.  The  normoblast  is  a  daughter-cell  of 
the  megaloblast  and  is  of  somewhat  smaller  size,  containing  more  hemo- 
globin, with  a  somewhat  denser  nucleus,  with  larger  net-knots;  this  corre- 
sponds to  the  sauroid  stage  of  Minot,  the  significance  of  which  term  is  the 
same  as  explained  above  for  ichthyoid.  The  erythroblast  differs  from  the 
normoblast  in  having  an  increased  amount  of  hemoglobin,  but  mainly  in 
its  smaller,  more  compact  nucleus.  This  cell  becomes  an  erythroplastid 
through  loss  of  nucleus.  (It  conduces  to  simplicity  and  clearness  to  regard 
the  megaloblast  and  normoblast  as  two  developmental  phases  of  the  erythro- 
blasts.)  The  manner  by  which  the  nucleus  disappears  has  been  much 
disputed.  It  has  been  held  to  be  absorbed  (karyolysis) ;  Howell  has  de- 
scribed its  extrusion  either  as  a  single  or  fragmented  body  (karyorrhexis) 
in  the  cat;  Emmel  (Amer.  Jour.  Anat.,  16,  2,  1914)  has  recently  de- 
scribed for  pig  a  process  by  which  the  red  corpuscle  arises  through  budding, 
leaving  a  nucleated  remnant. 

Certain  erythroblasts  may  be  smaller  than  the  average,  others  larger; 
these  dimentionally  atypical  forms  are  termed  respectively  microcytes  and 
megalocytes. 

The  large  lymphocyte  of  the  blood  is  believed  to  be  derived  from  the 
primitive  blood-cells  by  slight  differentiation;  perhaps  it  represents  a  po- 
tential hemoblast.  The  small  lymphocyte  is  simply  a  daughter-cell  of  a 
large;  a  large,  a  grown  small  lymphocyte. 


218  BLOOD 

The  primitive  blood-cell  may  by  slight  differentiation  become  a  leuko- 
blast;  according  to  whether  the  cytoplasm  elaborates  neutrophilic,  acido- 
philic,  or  basophilic  granules,  it  becomes  a  polymorphonuclear  neutrophil, 
eosinophil,  or  basophil  ('mast-cell')  leukocyte.  The  transition  stage,  from 


FIG.  231.  —  DIAGRAMMATIC  ILLUSTRATIONS  OF  SUCCESSIVE  STAGES  IN  THE  TRANS- 
FORMATION OF  THE   MAMMALIAN  ERYTHROCYTE    (a)   TO  FORM  THE  EUYTHRO- 

PLASTID    (/). 

6  and  c,  by  extrusion  of  the  nucleus  as  a  whole;  d  and  e,  by  extrusion  of  the  frag- 
mented nucleus. 

the  standpoint,  of  the  nucleus,  between  the  leucoblast  with  spherical  nucleus 
and  the  granulocyte  with  polymorphous  nucleus,  is  the  large  mononuclear 
leukocyte  (transitional  leukocyte).  According  to  Kyes  (1915),  certain  large 
mononuclear  leukocytes  are  derived  from  the  reticulum  of  lymph  nodes.  Both 
the  reticular  cells  and  their  leukocyte  derivatives  are  said  to  be  phagocytic. 
Giant  cells  are  derived  from  the  leukoblast,  or  perhaps  primitive  blood- 
cell,  along  a  separate  line  of  differentiation,  characterized  by  absence  of  cy- 


FIG.  232. — SUCCESSIVE  STAGES  IN  THE  ELIMINATION  OF  THE  ERYTHROBLAST  NU- 
CLEUS,  FROM    HOMOPLASTIC    CULTURES   OF   BLOOD   OF  A   32   MM.    PlG  EMBRYO. 

This  is  regarded  by  Emmel  as  a  'somewhat  imperfect  case  of  constriction,'  but 
it  illustrates  the  fundamental  similarity  between  erythroplastid  formation  by  ex- 
trusion of  nucleus  (Howell)  and  by  cytoplasmic  constriction.  (After  Emmel,  Amer. 
Jour.  Anat.,  16,  2,  1914.) 

toplasmic  division,  excessive  growth,  and  giant  or  multiple  nucleus.  The 
multinucleate  condition  is  attained  apparently  by  both  mitotic  and  amitotic 
division  of  the  nucleus.  From  the  megakaryocyte  pseudopodia  are  derived 
the  blood-platelets  as  explained  above.  Blood  development  in  marrow  passes 
through  the  same  phases,  the  hemoblast  stage  here  being  generally  known  as 
the  myeloblast,  and  characterized  by  a  considerable  finely  granular  neutro- 
philic cytoplasmic  content.  The  above  is  given  in  outline  in  the  following 
scheme,  adapted  largely  from  the  work  of  Maximow  on  hemopoiesis  in  the 
rabbit  embryo.  (Arch.  mikr.  Anat.,  Bd.  73,  1909.) 


219 


220 


BLOOD 

BONE-MARROW 


The  red  variety  of  bone-marrow,  found  in  the  flat  bones  generally 
and  in  the  epiphyses  of  long  bones,  functions  as  the  sole  hemopoietic  or- 
gan of  later  fetal  and  adult  life.  According  to  certain  authorities  it  is 
assisted  in  this  function  to  some  extent  by  the  spleen.  Besides  a  hemo- 
poietic function,  red  bone-marrow  possesses  also  the  capacity  of  de- 


FIG.  233. — FROM  A  SECTION  OF  RED  MARROW  OF  A  HUMAN  BONE. 
o,  giant  cell;  h,  leukocytes;  c,  nucleated  red  blood  cells;  d,  mitosis  in  a  marrow 
cell;  e,  outline  of  a  fat  cell;  /,  reticulum;  g,  mitosis  in  a  giant  cell.     X  680.     (After 
Bohm  and  von  Davidoff.) 

straying  worn-out  red  blood-corpuscles.  In  this  process  it  is  assisted 
greatly  also  by  the  spleen  and  lymphoid  organs  generally.  The  phago- 
cytic  leukocytes  of  these  locations  are  largely  active  in  this  destructive 
process  and  in  the  transportation  of  the  hemoglobin  debris  to  the  liver 
where  as  hematoidin  it  is  apparently  appropriated  in  the  manufacture 
of  the  bile  pigment,  bilirubin. 

The  generic  name  for  the  specific  hemogenic  cells  of  marrow  is 
myelocyte.  This  includes  the  parent  blood-cell  (hemoblast)  and  the 
intermediate  developmental  stages  of  both  white  (lymphocytes,  mono- 
nuclear  leukocytes — leukoblasts)  and  red  (megaloblast,  normoblast, 
erythroblast  stages)  cells.  Besides  these,  there  are  of  course  abundantly 
present  also  the  adult  forms  of  blood -cells  both  white  (eosinophil,  neu- 
trophil,  and  basophil  polymorphonuclear  leukocytes,  and  lymphocytes) 
and  red  (erythroplastids).  Potential  osteoblasts  and  osteoclasts  are 


BONE-MAEROW 


221 


also  present,  but  indistinguishable  from  the  lymphocytes  and  hemogenic 
polykaryocytes  respectively  unless  specially  stained. 

A  description  of  the  cells  in  their  order  of  hemogenic  cytomorphosis 
follows : 

1.  Myeloblast  (Premyelocyte;  Hemoblast,  Mesameboid  Cell;  Prim- 
itive Blood  Cell;  'Lymphocyte'). — This  is  the  parent  blood-cell  of  bone- 


FIG.  234. — TYPES  OF  CELLS  FROM  A  SMEAR  PREPARATION  OF  THE  MARROW  OF  A 

HUMAN  RIB. 

1,  red  blood  corpuscles;  2,  nucleated  red  blood  cells,  erythroblasts;  3,  small  lympho- 
cytes; 4,  large  mononuclear  cells  with  neutrophil  granules;  5,  polynuclear  neutro- 
phil;  6,  eosinophil  cells;  7,  a  basophil  cell.  Eosin  and  methylene  blue.  Nocht's 
stain.  X  1200. 

marrow.  It  produces  by  proliferation  and  slight  differentiation  the  more 
direct  ancestors  of  both  the  white  (leukoblast)  and  red  (megaloblast- 
erythroblast)  cells.  Mother-  and  daughter-cells  are  similar  in  their 
relatively  large  granular  nuclei,  well  developed  cell-body,  ameboid  capac- 
ity, and  proliferative  activity.  The  cytoplasm  of  the  myeloblast  is  homo- 
geneous or  very  finely  granular  and  slightly  basophilic ;  likewise  the 
leukoblast.  The  megaloblast  may  be  distinguished  by  its  slightly  oxyphil 
character  due  to  the  presence  of  a  small  amount  of  hemoglobin. 


222  '  BLOOD 

2.  Lymphocytes. — These  include  larger  and  smaller  varieties.  They 
are  similar  to,  and  in  part  identical  with,  the  ahove-described  cells,  the 
myeloblasts.     They  include  both  cells  differentiated  from  marrow  and 
cells  transported  by  the  blood  stream.     They  are  indistinguishable  from 
the  osteoblast.    In  short,  these  several  cells  of  similar  characteristics  may 
be  identical  in  their  capacity  to  function  as  progenitors  of  blood-cells, 
and  may  represent  the  parent  blood-cell.  • 

3.  Large  Mononuclear  Leukocytes. — These  cells  are  distinguished 
from  the  myeloblasts  and  lymphocytes  only  by  their  slightly  modified 
nucleus,  and  by  the  occasional  presence  of  a  small  number  of  fine  neu- 
trophilic  granules.     The  nucleus  is  oval  or  bean-shaped.     It  represents 
a  transition  phase  between  the  less  differentiated  lymphocyte  stage  and 
the  granulocytes.    It  contains  a  centrosome  located  usually  in  that  por- 
tion of  the  cytoplasm  lying  in  the  concavity  -of  the  bent  nucleus.    This 
cell  may  proliferate  extensively. 

4.  Polymorphonuclear  Neutrophil  Granulocytes.— These   include 
a  graded  series  of  stages  from  the  standpoint  of  shape  of  nucleus,  and 
amount  of  granular  content.     The  younger  stages  contain  a  less  com- 
plicated nucleus,  generally  bean-shaped  with  centrosome  and  relatively 
fewer  (some  basophilic,  'unripe')  granules;  these  have  a  slight  prolifera- 
tive  capacity.    Older  stages  have  progressively  more  complicated  nuclei, 
characterized  by  a  lobulated  chain  (with  from  two  to  five  segments)  of 
dense  chromatin,  and  are  no  longer  capable  of  mitotic  division. 

5.  Eosinophil  Granulocytes. — These  cells  resemble  the  neutrophils 
in  their  graded  series  of  nuclear  forms,  ending  in  a  lobulated  poly- 
morphous nucleus ;  but  differ  in  the  matter  of  size  and  staining  capacity 
of  the  cytoplasmic  granules.    These  granules  are  of  fairly  uniform  size 
and  of  spherical  shape,  but  much  larger  than  the  neutrophilic  granules, 
and  are  strongly  acidophilic,  showing  special  affinity  for  the  cytoplasmic 
stain,  eosin.     In  the  younger  forms  the  granules  are  basophilic.     The 
older  types  are  identical  with  those  of  the  blood.     Again,  only  the  less 
differentiated,  that  is,  those  with  oval  nucleus  and  a  centrosome,  may 
divide  mitotically. 

The  commonly  accepted  view  of  the  origin  of  neutrophilic  and  oxy- 
philic  cytoplasmic  granules  is  that  they  arise  intracellularly  under  nuclear 
influence,  perhaps  from  less  differentiated  nuclear  extrusions  or  chro- 
midia.  Originally  these  granules  are  basophilic  ('unripe').  However, 
Weidenreich  regards  the  eosinophil  granules  as  the  ingested  hemoglobin 
particles  of  degenerating  and  fragmenting  erythroplastids.  Their  con- 
siderable presence  in  red  marrow  and  spleen  where  blood-cell  disintegra- 


BONE-MAEEOW  223 

tion  is  extensive,  lends  weight  to  this  hypothesis.  Likewise  Badertscher 
(Amer.  Jour.  Anat.,  15,  1,  1913)  finds  that  eosinophil  leukocytes  and 
free  eosinophilic  granules  are  very  abundant  in  the  vicinity  of  degenerat- 
ing muscles  in  salamanders  during  the  time  when  the  gills  atrophy,  and 
believes  that  the  eosinophilic  granules  are  ingested  fragments  of  degener- 
ated muscles  and  red  blood-corpuscles.  Eosinophils  do  undoubtedly  in- 
crease greatly  in  number  during  certain  infectious  diseases  characterized 
by  extensive  tissue  disintegration,  e.g.,  trichiniasis ;  but  disproof  of  intra- 
cellular  origin — a  teaching  more  in  accord  with  our  knowledge  of  cyto- 
plasmic  granule  origin  through  protoplasmic  activity — demands  direct 
evidence  of  extensive  granular  ingestion,  which  is  lacking.  Moreover, 
the  microchemical  nature  of  eosinophil  granules  differs  from  that  of 
hemoglobin;  also,  they  differentiate  from  basophilic  granules  and  in 
hemogenesis  in  the  turtle,  for  example,  eosinophils  appear  before  hemo- 
globin-containing cells  are  present.  The  free  eosinophil  granules  in 
degenerating  tissues  are  more  likely  derived  from  disintegrating  eosino- 
phils, abundant  in  such  regions. 

6.  Basophil  Granulocytes (Mast  cells}. — These  are  identical  with 
the  mast  leukocytes  of  the  blood,  and  possibly  also  with  the  cells  of  this 
name  in  connective  tissue,  the  latter  perhaps  representing  degenerating 
phases  of  the  former.     They  are  characterized  by  a  variable  polymor- 
phous nucleus,  apparent  lack  of  centrosome,  extremely  slight  prolifera- 
tive  capacity,  and  presence  of  spheroidal  non-uniform  basophilic  cyto- 
plasmic  granules.  :  They  are  numerically  increased  in  marrow  and  the 
circulating  blood  and  in  the  spleen  in  certain  diseases. 

7.  Giant  Cells  or  Myeloplaxes. — These    are    relatively    enormous 
cells  (of  30  to  100  microns  diameter).     They  may  have  either  a  single 
large,  frequently  lobulated  annular,  nucleus  (megakaryocyte)  or  several, 
even  many,  nuclei  (polykaryocyte).     The  megakaryocyte  is  a  derivative 
of  the  lymphocyte  (myeloblast).     The  polykaryocyte  represents  a  later 
modification  of  the  megakaryocyte,  the  lobulated  nucleus  having  become 
broken  up  into  separate  nuclei.    These  polykaryocytes  ('hemogenic  giant- 
cells')  have  been  erroneously  regarded  as  identical  with  the  multinucle- 
ated  osteoclasts.    They  are  in  fact  .potential  erythroblasts,  comparable  to 
'blood-islands,'    with    only    slight    or    no    phagocytic    capacity.      After 
Wright's  technic  the  cytoplasm  of  these  cells  presents  fine  purple  gran- 
ules.    Osteoclasts  do  not  contain  such  'metachromatic'  granules.     The 
polykaryocyte  of  the  yolk-sac  of  the  10-millimeter  pig  embryo  can  be  seen 
to  differentiate  into  erythrocytes,  a  hemoglobin-containing  area  developing 
about  the  several  nuclei,  the  whole  finally  breaking  up  into  an  equal  num- 

15 


224  BLOOD 

her  of  red  cells.  Giant  cells  are  characteristic  elements  of  all  hemopoietic 
organs.  The  megakaryocytes  protrude  long  pseudopodia  which  segment 
into  blood-platelets  (Wright),  abundantly  present  in  red  marrow. 

8.  Erythrocytes.— These  cells  include  the  several  developmental 
forms  of  red  cells :  (a)  megaloblast,  (b)  normoblast,  (c)  erythroblast  and 
(d)  erythroplastid.  The  megaloblast  is  very  similar  to  the  leukoblast  ex- 
cept that  the  cytoplasm  contains  a  slight  amount  of  hemoglobin,  and 
therefore  gives  an  oxyphilic  staining  reaction.  The  nucleus  is  granular, 
with  a  delicate  chromatic  network.  This  is  the  so-called  ichthyoid  stage  of 
Minot.  Xormoblast  and  erythroblast  are  closely  similar  stages  (sauroid 
stage  of  Minot),  characterized  by  the  relatively  smaller  and  denser  more 
chromatic  nucleus,  and  a  relatively  more  extensive  shell  of  cytoplasm 
with  increasingly  more  hemoglobin.  The  erythroplastid  develops  from 
the  erythroblast  through  loss  of  nucleus,  generally  by  extrusion. 

Evans  (Amer.  Jour.  Physiol.,  37,  2, 1915)  has  directed  attention  anew  to 
the  phagocytic  large  mononuclear  leukocytes,  the  'macrophages'  of  Metsch- 
nikoff  (1892).  On  the  basis  of  a  specific  response  to  vital  azo  dyes  he  iden- 
tifies them  as  a  group  distinct  from  the  large  mononuclear  elements  and 
lymphocytes  of  the  blood,  and  includes  among  them  certain  endothelial  and 
reticular  cells  and  the  'clasmatocytes'  (Ranvier)  or  'resting  wandering  cells' 
(Maximow)  of  connective  tissue,  all  of  which  may  become  free  macrophages. 
These  cells  in  mammals,  of  round  or  elongated  shape,  range  in  diameter 
from  about  10  to  30  microns;  they  contain  a  stoutly  cresentic  nucleus  of 
irregular  contour  and  excentric  position;  the  cytoplasm  is  weakly  baso- 
philic,  covered  with  delicate  pseudopods  of  various  sizes,  and  frequently 
filled  with  large  vacuoles.  As  endothelial  cells  they  may  line  the  capillaries 
and  venules  of  the  liver  ('von  Kuppfer  cells'),  spleen,  red  bone-marrow, 
hemal  glands,  and  the  lymphatic  sinuses  of  lymph  nodes.  They  include 
also  reticular  cells  of  lymph  nodes,  spleen  pulp  and  bone-marrow,  and  the 
"clasmatocytes  of  connective  tissue.  As  free  cells  they  occur  in  the  serous 
cavities,  lymph  sinuses  of  lymph  nodes,  spleen  and  hepatic  capillaries. 
They  are  abundant  in  transudates  and  exudates  in  serous  cavities.  Only 
under  pathological  conditions  do  they  appear  in  the  peripheral  blood  stream. 
Weidenreich  identified  them  with  the  large  mononuclear  leukocytes  of  the 
blood  and  lymph.  Evans'  experiments,  on  the  contrary,  give  no  indication 
that  leukocytes  are  converted  into  these  cells.  They  originate  chiefly  from 
endothelia.  They  are  phagocytes  and  are  active  also  in  the  normal  physio- 
logical processes.  They  handle  the  blood  and  bile  pigments,  and  fats  and 
lipoids.  The  protoplasm  of  the  macrophages  is  characterized  especially 
by  its  response  to  finely  particulate  matter.  Macrophages  share  the  func- 
tion of  phagocytosis  with  the  polymorphonuclear  elements  of  the  blood. 


CHAPTEE    IX 
THE   LYMPHATIC    SYSTEM 

The  lymphatic  series  includes  a  system  of  lymphatic  channels  which 
collect  the  lymph  from  the  various  tissues  of  the  body  and  return  it 
to  the  large  veins  of  the  neck,  where  it  mixes  with  the  blood.  In  the 
course  of  this  lymph  vascular  system  are  various  aggregations  of  lym- 
phoid  or  adenoid  tissue  which  occur  in  the  form  of  lymph  nodules  or 
follicles,  lymph  glands  or  nodes,  and  the  lymphoid  organs.  These  or- 
gans are  the  tonsils,  thymus,  and  spleen.  The  lymphatic  vessels  also 
stand  in  intimate  relation  if  not  in  direct  communication  with  the 
serous  and  synovia!  membranes  and  the  bursae. 


LYMPH 

Like  the  blood,  the  lymph  may  be  considered  as  a  primary  tissue 
whose  intercellular  elements  are  entirely  of  a  fluid  nature.  In  most 
portions  of  the  body,  lymph  is  a  colorless  fluid  which  is  scantily  provided 
with  corpuscular  elements,  the  lymphatic  corpuscles.  The  lymphatic 
corpuscles  are  identical  with  the  leukocytes  of  the  blood.  In  the  lymph 
most  of  these  cells  are  of  the  mononuclear  form,  the  small  mononuclears 
or  lymphocytes  being  the  most  abundant.  Lymph  also  contains  a  small 
proportion  of  polymorphonuclear  cells,  which  not  only  are  derived  from 
the  lymphoid  tissues,  but  as  wandering  cells  find  their  way  into  the 
lymphatic  vessels  from  the  tissues  generally.  Blood-platelets  are  not 
present  in  lymph  (Howell)  ;  prothroinbin  is  liberated  by  the  lymphocytes. 

The  cells  of  lymph,  predominantly  of  the  small  lymphocyte  type,  are 
derived  from  the  numerous  lymphoid  masses  (nodes  and  nodules) 
through  which  the  lymph  passes  on  its  way  from  the  tissues  to  the  sub- 
clavian  veins.  According  to  Davis  and  Carlson  (Amer.  Jour.  Physiol., 
vol.  25,  1909)  the  number  of  lymphocytes  contributed  to  the  blood  daily 
may  be  more  than  the  total  permanently  present  in  the  blood.  Since  the 
number  in  a  cubic  millimeter  remains  fairly  constant,  a  number  must 

225 


226  THE  LYMPHATIC  SYSTEM 

be  daily  consumed  in  the  body  equal  to  the  number  added  to  the  blood. 
Many  of  course  actually  suffer  destruction,  but  it  seems  probable  that 
a  considerable  number  also  first  undergo  differentiation  into  granulocytes, 
and  perhaps  as  potential  hemoblasts  may  function  as  parent  cells  of 
erythrocytes. 

In  addition  to  the  leukocytes  lymph  contains  fat  globules  and  glyco- 
gen.  These  are  mostly  the  products  of  absorption  from  the  intestinal 
tract,  in  which  process  the  lymphatic  vessels  play  an  important  role.  In 
the  lymphatic  vessels  of  the  intestine  during  absorption  fat  globules  are 
so  abundant  as  to  impart  to  the  lymph  a  milky  white  color;  this  variety 
of  lymph  is  termed  the  chyle.  These  fat  globules  are  rapidly  removed 
by  the  lymphoid  organs,  since  even  in  the  presence  of  abundant  chyle 
only  comparatively  few  fat  globules  escape  into  the  general  blood  current. 
The  lymph  of  other  portions  of  the  body  than  the  abdominal  region, 
therefore,  contains  relatively  little  fat. 

The  lymph,  unlike  the  blood,  circulates  in  but  one  direction,  viz., 
toward  the  heart.  .It  must  therefore  be  formed  in  the  tissues  generally. 
The  blood  plasma  constantly  escapes  through  the  walls  of  the  capillary 
vessels  into  the  surrounding  lymphatic  spaces  of  the  tissues.  It  is  these 
tissue  spaces  which  have  been  considered  as  forming  the  beginning  of 
the  lymphatic  system.  Eecent  evidence,  however,  goes  to  show  that  the 
tissue  spaces  are  not  directly  connected  with  the  lymphatic  vessels,  but 
that  just  as  the  plasma  exudes  into  the  tissue  spaces  by  processes  of 
secretion,  osmosis,  and  filtration,  so  the  tissue  juices,  as  the  predecessors 
of  lymph,  enter  the  lymphatic  vessels  by  similar  processes  of  secretion, 
osmosis,  and  filtration.  Lymph  is  also  formed  by  absorption,  which  oc- 
curs chiefly  in  the  alimentary  tract. 

Under  favorable  conditions  the  lymph  will  coagulate,  though  more 
slowly  than  blood,  the  fibrin  forming  a  firm,  colorless  clot  in  which  the 
leukocytes  are  entangled.  Because  of  their  tendency  to  adhere  to  the 
sides  of  the  vessel — thus  circulating  at  the  periphery  of  the  current — 
the  lymph  cells  are  most  likely  to  be  found  at  the  periphery  in  those 
post-mortem  clots  which  occur  within  the  lymphatic  vessels. 


LYMPHATIC   VESSELS 

(Lymphatics) 

The  lymphatic  vessels  vary  in  size  from  that  of  the  smallest  capillary 
vessels  up  to  that  of  the  thoracic  duct.     The  smaller  vessels,  lymphatic 


LYMPHATIC  VESSELS  227 

capillaries,  form  anastomosing  meshes  in  all  tissues  where  blood  capil- 
laries are  found.  They  are  most  abundant  in  the  perivascular  connective 
tissues,  where  they  form  a  dense  plexus  about  the  wall  of  the  blood-ves- 
sels. 

The  wall  of  the  lymphatic  capillary,  like  that  of  the  blood  capillary, 


FIG.  235. — SUBCUTANEOUS  LYMPHATIC  VESSEL  OF  A  FETAL  PIG. 

At  the  right  is  a  small  blood-vessel.     Hematein  and  eosin.     Highly  magnified. 
(After  MacCallum.) 

consists  of  a  single  layer  of  endothelium.  This  endothelium  probably 
forms  a  complete  lining  for  the  lymphatic  capillary  and  is  continuous 
through  larger  and  larger  vessels  with  that  of  the  veins,  from  which, 
according  to  Sabin  (Amer.  Jour.  Anat.,  1902),  the  lymphatics  are 
originally  developed. 

The  relation  of  the  lymphatic  capillaries  to  the  tissue  spaces  is  not 
as  yet  definitely  settled.    It  was  formerly  thought  that  these  spaces  were 


228  THE  LYMPHATIC  SYSTEM 

continuous  with  the  lymphatic  capillaries,  but  the  more  recent  observa- 
tions,, represented  by  those  of  MacCallum  (Johns  Hop.  Hosp.  Bull., 
1903),  seem  to  show  that  the  capillaries  of  the  lymphatic  system,  like 
those  of  the  blood  vascular  system,  form  a  series  of  branching  channels 
which  are  open  only  toward  the  veins.  According  to  this  conception, 
therefore,  the  tissue  juices,  formerly  also  considered  as  lymph,  are  con- 
tained within  a  separate  series  of  channels,  the  tissue  spaces  and  lym- 
phatic canaliculi,  and  they  enter  the  true  lymphatics  only  by  processes  of 
osmosis  and  the  secretory  activity  of  the  lymphatic  endothelia. 


FIG.  236. — THE  GROWING  END  OF  A  DEVELOPING  LYMPHATIC  VESSEL  IN  THE  SUB- 
CUTANEOUS TISSUE  OF  A  FETAL  PIG. 

The  lumen  of  the  vessel  has  been  filled  with  a  dark  injection  mass.    Highly  mag- 
nified.    (After  MacCallum.) 

The  lymphatic  capillaries  are  of  rather  irregular  caliber,  generally 
greater  than  that  of  blood  capillaries,  and  possess  frequent  sinus-like 
dilatations,  which  peculiarity  is  also  characteristic  of  the  larger  lym- 
phatic vessels. 

The  lymphatic  capillaries  soon  acquire  an  adventitial  sheath  of  fibro- 
elastic  tissue  and  pass  into  the  smaller  lymphatic  vessels.  On  attaining 
a  size  of  from  0.2  to  0.8  millimeter  their  wall  is  differentiated  into  the 
same  three  coats  which  are  found  in  the  veins.  Except  for  the  fact 
that  they  contain  lymph  instead  of  blood,  these  vessels  closely  resemble 
the  small  veins,  and  like  some  of  the  latter  vessels  they  possess  frequent 
valves. 


LYMPHATIC  VESSELS 


229 


The  tunica  intima  of  the  lymph  vessel  consists  of  an  endothelial 
lining  with  a  thin  delicate  fibre-elastic  memhrane.  The  tunica  media  is 
thin  and  contains  circular  smooth  muscle  fibers.  The  adventitia  is  the 
thickest  coat  of  the  lymph  vessel.  It  consists  of  fibro-elastic  connective 
tissue  and  longitudinally  disposed  bundles  of  smooth  muscle  fibers. 

The  wall  of  the  lymph  vessels  is  supplied  with  small  blood-vessels  and 
nerves,  in  the  same  manner  as  the  veins.  The  nerves  form  a  plexus  in 


Fie.  237. — LYMPHATIC  AND  BLOOD  VESSELS  IN  THE  HILUM  OF  A  HUMAN  LYMPH-NODE. 
a,  lymph  vessels;  b,  blood-vessels.     Hematein  and  eosin.     Photo.     X  160. 

the  adventitia  from  which  branches  are  distributed  to  the  media  and 
iutima.  Kytmanof  (Anat.  x\nz.,  1901)  has  traced  the  fine  nerve  fibrils 
to  the  smallest  lymphatic  capillaries,  where,  as  in  the  intima  of  the 
larger  vessels,  they  end  in  close  relation  to  the  endothelial  cells. 

To   summarize:   the   lymphatic   capillaries   arise   by   one   of   three 
methods : 

1.  As  lymphatic  plexuses  in  all  connective  tissues;  the  most  abun- 
dant of  these  are  the  perivascular  lymphatics. 

2.  As  dilated  pouches  having  blind  extremities,  as  in  the  villi  of 
the  small  intestine,  where  they  are  known  as  lacteals. 


230  THE  LYMPHATIC  SYSTEM 

3.  By  direct  communication  with  the  stomata  of  the  serous  mem- 
branes. The  presence  of  true  stomata  in  the  serous  membranes  of  man 
with  the  exception  of  possibly  certain  portions  of  the  peritoneum  is  dis- 
puted. 

The  lymph  is  derived  from  the  tissue  juices  and  by  absorption  from 
the  alimentary  tract,  and  is  conveyed  by  the  lymphatic  capillaries  to 


FIG.  238. — LYMPHATIC  CAPILLARY  FROM  THE  SPERMATIC  CORD  OF  A  DOG,  SHOWING 
NERVE  ENDINGS. 

a,  nerve  fibers.    Methylene  blue.    Highly  magnified.     (After  Kytmanof.) 

larger  and  larger  lymph  vessels,  which  resemble  the  small  veins  in  their 
structure,  and  which  finally  empty  into  the  subclavian  veins  of  the  neck, 
at  their  junction  with  the  internal  jugulars. 

The  main  lymph  channels  are  the  thoracic  duct  on  the  left,  and  the 
right  lymphatic  dubt.  Only  the  thoracic  duct  drains  the  abdominal 
lymphatics  and  is  thus  much  the  larger  vessel.  Toward  its  distal  end 
it  expands  into  a  receptacle  for  the  absorbed  chyle,  the  cisterna  chyli. 


THE  DEVELOPMENT  OF  LYMPH  VESSELS 

According  to  Sabin  the  mammalian  lymphatic  system  has  its  primary 
origin  in  two  paired  and  one  unpaired  venous  sprouts :  the  jugular,  inguinal 
(sciatic),  and  mesenteric  (retroperitoneal)  lymph  sacs.  Certain  investi- 
gators (Huntington,  Mem.  Wistar  Inst.,  1911;  McClure,  Anat.  Eec.,  6,  6, 


THE  DEVELOPMENT  OF  LYMPH  VESSELS  231 

1912,  and  others)  interpret  these  sacs  as  the  products  of  fusions  of  still 
more  primitive  discrete  lymphatic  anlages  which  arose  as  mesenchymal 
spaces;  and  their  connection  with  the  subclavian,  sciatic  and  renal  veins 
as  secondary  unions.  Sabin  and  others  regard  the  lymphatic  endothelium 
once  having  sprouted  from  the  venous  endothelium  as  strictly  specific,  and 
the  entire  lymphatic  system  as  a  derivative  by  sprouting  and  fusion  of 
these  three  sets  of  anlages. 

Huntington  and  McClure  derive  the  definitive  lymphatic  system  by 
a  progressive  fusion  of  isolated  mesenchymal  spaces  (mainly  in  the  extra- 
intimal  portion  of  disappearing  veins)  and  cells  in  the  paths  of  the 
future  lymphatic  trunks.  According  to  the  one  school  lymphatic  endo- 
thelium can  arise  only  by  proliferation  of  preexisting  endothelium;  accord- 
ing to  the  other,  endothelium  can  continually  differentiate  from  young 
mesenchyma. 

The  recent  observations  of  Clark  (Anat.  Rec.,  3,  4,  1909)  on  the 
growing  lymphatics  in  the  tail  of  living  frog  tadpoles  where  the  process 
of  sprouting  could  be  clearly  followed,  leaves  no  room  for  doubt  that 
lymphatics  spread  through  sprouting,  but  the  material  and  data  give  no 
information  as  to  the  manner  of  origin  of  the  initial  anlages,  which  is 
the  real  question  at  issue.  It  is  perhaps  as  yet  too  early  to  decide  the  mat- 
ter on  the  basis  of  available  evidence,  but  the  extensive  histologic  data  of 
Huntington  and  McCluro  strongly  support  their  claim  of  primary  lym- 
phatic origin  by  confluence  of  isolated  mesenchymal  spaces. 

The  beautiful  injections  of  Miss  Sabin  which  show  a  progressively 
enlarging  continuous  system  in  pig  embryos  apparently  flatly  contradict 
this  hypothesis;  but  the  objection  cannot  be  fairly  ignored  that  the  advo- 
cates of  lymphatic  origin  through  fusion  of  isolated  spaces  base  their 
claims  on  appearances  before  the  establishment  of  a  continuous  system 
or  even  the  several  sets  of  lymphatic  sacs,  and  the  further  fact  that  the 
injection  method  is  unsuitable  for  revealing  lymphatic  anlages  existing 
as  isolated  spaces.  As  concerns  endothelium  in  general,  Huntington 
(Amer.  Jour.  Anat.,  16,  3,  1914)  regards  an  endothelial  cell  as  simply 
an  adaptive  form  of  a  mesenchymal  cell,  'modified  in  accordance  with 
definite  hydrostatic  and  other  purely  mechanical  factors,'  resulting  from 
the  presence  of  blood  or  lymph.  On  drainage  of  the  fluid  and  consequent 
release  of  pressure,  the  endothelial  cell  is  believed  to  be  capable  of  again 
reverting  to  'the  type  of  the  indifferent  mesenchymal  cell.'  Kampmeier 
(Amer.  Jour.  Anat,  17,  2,  1915)  presents  evidence  from  a  study  of  sec- 
tions of  the  young  toad  embryo  apparently  demonstrating  the  primary 
origin  of  lymphatic  endothelium  only  from  venous  endothelium;  but  the 
primary  sacs  and  ducts  arise  by  a  confluence  of  these  earlier  discrete 
venous  buds.  A  concise  discussion  and  summary  of  this  subject  is  given  by 
McClure  (Anat.  Rec.,  9,  7,  1915.) 


232  THE  LYMPHATIC  SYSTEM 


THE  SEROUS  MEMBRANES 

The  serous  membranes  form  closed  sacs  which  line  the  great  cavities, 
of  the  body  and  are  reflected  over  the  viscera  to  form  a  double  covering, 
the  two  layers  of  which  are  freely  movable  over  one  another.  Of  these 
two  layers  the  one,  the  parietal  layer,  is  attached  to  the  wall  of  the  body 
cavity,  the  other,  the  visceral  layer,  covers  the  surface  of  the  inclosed 
organ. 

The  serous  membranes  consist  of  a  mesothelial  lining  and  a  support- 
ing membrane  of  areolar  connective  tissue  which  is  richly  supplied  with 

capillary  blood-vessels  and  lym- 
phatics. The  mesothelium  con- 
sists of  large  flat  cells,  pave- 
ment epithelium,  whose  ser- 
rated margins  are  firmly  united 
by  an  intercellular  cement  sub- 
stance. Here  and  there  mi- 
nute openings  are  seen  which 
FIG.  239. — TRANSECTION  OP  THE  PERICAR-  are  surrounded  by  very  small 
DITJM  OF  A  CHILD.  mesothelial  cells;  these  stoma ta 

a~a,  mesothelium;  b-b,  submesothelial  con-     have  been  found  to  be  in  cer. 
nective  tissue.    Hematein  and  eosm.    Photo. 

x  500.  tain  instances  directly  connect- 

ed   with    the    lymph    vessels. 
Some  regard  them  as  transient  fenestra,  others  as  artifacts. 

Tunica  Propria. — The  mesothelium  rests  upon  a  layer  of  areolar 
tissue  which  is  richly  supplied  with  small  blood-vessels  and  lymphatics, 
forming  an  abundant  vascular  plexus  beneath  the  mesothelium.  The 
serous  membrane  is  either  directly  united  to  the  wall  of  the  cavity  and 
the  surface  of  the  organ  which  it  envelops,  or  it  may  be  attached  by  a 
loose  layer  of  submesothelial  connective  tissue. 

The  thickness  of  the  mesothelial  cells  varies  in  different  portions 
of  the  serous  membranes  and  is  somewhat  dependent  upon  the  age  of  the 
individual.  In  most  portions  it  is  no  more  than  a  pavement  epithelium, 
but  over  the  surface  of  the  functionally  active  ovary  these  cells  are 
much  thickened  and  acquire  a  cuboidal  shape ;  thus  it  forms  the  'germinal 
epithelium'  of  the  ovary.  In  young  individuals,  viz.,  in  fetal  life  and 
early  childhood,  the  cuboidal  cell  type  is  found  in  many  portions  of 
the  peritoneum,  pleura,  and  pericardium. 

The  synovial  membranes  resemble  the  serous  in  their  structure.  They 


LYMPH  NODULES 


233 


are  clothed  by  a  single  layer  of  pavement  cells  which  is  said  to  be  in- 
complete in  places.  This  epithelium  (mesenchymal  epithelium)  is  sup- 
ported upon  a  layer  of 
firm  fibrous  tissue 
richly  supplied  with 
both  lymph  and  blood 
capillaries.  In  the  re- 
cesses of  the  joints  the 
eynovial  membranes 
are  frequently  thrown 
into  small  villous 
folds,  which  are  chief- 
ly formed  by  the  inner 
portion  of  the  fibrous 
coat  and  are  covered 
with  epithelium; 
these  are  the  synovial 
villi. 

The  bursce  and  the 
synovial  sheaths  of  the 
tendons  are  of  similar 
structure. 

Both    the    serous 
and  the  synovial  mem- 
branes are  moistened  by  fluid  which  contains  leukocytes  in  small  num- 
bers, and  closely  resembles  the  lymph  and  tissue  juice  in  its  composition. 


FIG.  240. — SECTION  OF  A  VASCULAR  SYNOVIAL  VILLTJS 
FROM  THE  KNEE  JOINT  OF  A  CHILD. 

Hematein  and  eosin.    Photo.     X  200. 


LYMPH  NODULES 

(Lymph  Follicles) 

The  lymph  nodule  is  a  structural  unit  of  lymphoid  tissue  which  may 
exist  independently,  as  in  the  solitary  nodules  of  the  intestinal  tract,  or 
may  form  groups  or  accumulations  consisting  of  a  greater  or  less  number 
of  nodular  units.  In  this  latter  condition  they  occur  in  the  mucous 
membrane  of  the  small  intestine  as  Peyer's  patches,  in  the  tongue  as  the 
lingual  tonsil,  in  the  fauces  as  the  faucial  tonsils,  in  the  pharynx  as  the 
pharyngeal  tonsil,  in  the  wall  of  the  laryngeal  cavity,  in  the  spleen  as 
the  Malpighian  (splenic)  corpuscles,  in  the  lymph  nodes  as  the  peripheral 


234  THE  LYMPHATIC  SYSTEM 

lymph  nodules,  and  in  the  thymus,  where  we  may  consider  the  lobule 
of  the  organ  as  being  the  structural  equivalent  of  a  lymph  nodule. 

The  lymph  nodule  consists  of  a  mass  of  lymphoid  tissue,  usually  of 
ovoid  form,  which  is  surrounded  by  or  embedded  in  connective  tissue.  In 
those  locations  where  it  exists  independently  the  nodule  is  completely 


FIG.  241. — A  LYMPH  NODULE,  SOLITARY  FOLLICLE,  FROM  THE  LARGE  INTESTINE  OF 

MAN. 

In  the  upper  part  of  the  figure  the  edge  of  the  intestinal  mucosa  is  shown;  it  con- 
tains many  secreting  tubules  which  have  been  cut  in  transverse  or  oblique  section 
and  are  lined  by  columnar  epithelium  and  goblet  cells.  Photo.  X  80. 

surrounded  by  the  connective  tissue  in  which  it  lies.  In  other  places, 
as  in  the  lymph  nodes,  the  nodule  is  only  partially  surrounded  by  the 
connective  tissue  trabeculae  of  the  organ.  Not  only  do  fine  branches 
from  the  surrounding  connective  tissue  bundles  penetrate  the  periphery 
of  the  nodule,  but  the  reticulum  of  the  nodule  is  continuous  with  these 
trabeculas,  thus  forming  a  supporting  stroma  in  which  the  lymphocytes 
are  embedded. 


THE  LYMPH  NODES  235 

The  lymphocytes  are  loosely  packed  in  the  center  of  the  nodule,  and 
in  this  portion  cell  division  by  mitosis  is  most  active.  This  central  por- 
tion is  the  germinal  center  of  Flemming.  The  germinal  center  is  sur- 
rounded by  a  denser  circumferential  layer  of  lymphoid  tissue  in  which 
cell  division  is  less  active.  Between  this  denser  portion  and  the  sur- 
rounding connective  tissue  the  lymphocytes  are  again  more  loosely 
packed,  and  over  a  greater  portion  of  the  nodule  are  separated  from  the 
trabeculaB  by  a  lacuna-like  space,  the  peripheral  lymph  sinus. 

The  nodule  is  usually  supplied  with  a  thin-walled  artery,  occasionally 
two,  which  penetrates  to  the  middle  of  the  nodule  to  form  a  wide 
meshed  capillary  plexus.  The  capillaries,  at  the  periphery  of  the  nodule, 
unite  to  form  two  or  more  veins,  which  are  contained  in  the  adjacent 
connective  tissue. 

The  lymph  cells  are  mostly  of  the  mononuclear  type  ojE  leukocyte,  the 
small  mononuclear  or  lymphocyte  type  being  the  most  abundant.  Poly- 
morphonuclear  and  eosinophil  leukocytes  are  also  found  in  the  lymph 
nodules,  though  in  much  smaller  numbers.  Mitosis  is  most  frequently 
observed  in  the  large  mononuclear  type.  Because  of  the  nomadic  tend- 
encies of  the  leukocytes  the  boundaries  of  the  lobule  are  not  always 
sharp,  the  lymph  cells  frequently  infiltrating  the  surrounding  connective 
tissue  so  as  to  render  it  most  difficult  to  distinguish  the  latter  from  the 
true  lymphoid  tissue  of  the  nodule. 


THE  LYMPH  NODES 

(Lymph  Glands) 

These  structures  occur  in  the  course  of  the  lymph  circulation  in  vari- 
ous parts  of  the  body.  They  are  found  in  the  neighborhood  of  the 
large  joints,  as  in  'the  axilla,  the  groin,  the  popliteal  space,  in  the  pre- 
vertebral  and  mediastinal  connective  tissue  of  the  abdominal  and  thoracic 
cavities,  and  in  the  mesentery.  They  are  frequently  in  relation  with 
the  large  arteries,  e.g.,  the  renal,  internal  and  external  carotids,  etc. 

Each  lymph  node  consists  of  a  mass  of  nodular  lymphoid  tissue  in- 
closed within  a  fibro-elastic  connective  tissue  capsule.  The  capsule  also 
contains  a  little  smooth  muscle  tissue,  but  this  is  never  so  abundant  as  to 
form  any  considerable  portion  of  the  fibrous  membrane;  in  fact,  as  com- 
pared with  the  somewhat  similar  capsule  of  the  spleen,  that  of  the  lymph 
node  is  notably  deficient  in  smooth  muscle, 


236 


THE  LYMPHATIC  SYSTEM 


Afferent  LynphV<**e*> 


An  afferent  lymph  vessel,  pursuing  its  course  within  the  capsule, 
enters  the  lymph  node  by  a  number  of  subdivisions  which  penetrate  the 
deeper  layers  of  the  capsule  and  open  into  a  peripheral  lacunar  space, 
the  lymph  sinus,  which  separates  the  inner  surface  of  the  capsule  from 
the  adjacent  lymphoid  tissue,  but  which  is  bridged  across  at  frequent 
intervals  by  the  fine  strands  of  lymph  reticulum. 

The  lymphoid  tissue,  which  forms  the  substance  of  the  node,  consists 

of  a  dense  peripheral 

portion,    the    C  0  T  te  X  , 

formed  by  closely 
packed  lymph  nodules, 
and  a  looser  medulla  in 
which  are  columnar  ac- 
cumulations of  dense 
lymphoid  tissue,  the 
lymph  cords. 

Cortex.—  The  nod- 
ules of  the  cortex  are 
partially  separated 
from  each  other  by  sep- 
tum -  like  trabeculae 

which  extend  inward 
from  th 


FIG.  242.-DIAGRAMMATIC  ILLUSTRATION  OF  A  LYMPH     Sule>     EIld     &l°US 

NODE.  the    peripheral    lymph 

sinuses    are    continued 

into  the  substance  of  the  node  to  partially  surround  its  lymph  nodules. 

Each  lymph  nodule  is  thus  surrounded,  except  at  its  central  pole,  by 
a  peripheral  lymph  sinus,  into  which  the  afferent  lymphatic  vessels  pour 
their  contents.  The  lymph  on  entering  the  gland  is  thus  permitted  to 
enter  the  spaces  of  the  reticulum  and  percolate  through  the  lymph 
nodules  of  the  cortex  before  it  can  reach  the  looser  portions  of  the 
medulla.  Each  of  the  nodules  of  the  cortex  contains  a  germinal  center 
in  which  lymphocytes  are  actively  formed  by  mitosis,  and  from  which 
the  lymphocytes  readily  escape  along  the  lymph  channels  of  the  reticu- 
lum into  the  more  open  meshes  of  the  medulla. 

Medulla.  —  The  medulla  occupies  the  center  of  the  gland,  and  at 
one  point,  the  hilum,  it  reaches  the  surface.  At  this  point  a  considerable 
mass  of  fibrous  trabeculae  enters  the  medulla,  carrying  with  it  the  larger 
blood-vessels  to  be  distributed  to  all  portions  of  the  gland.  The  finer 


THE  LYMPH  NODES 


237 


ramifications  of  these  medullary  trabeculas  are  continuous  with  those 
of  the  cortex. 


Fia.  243. — TRANSECTION  OF  A  CERVICAL  LYMPH  NODE  OF  A  DOG. 

The  denser  portions  of  lymphoid  tissue  are  light  in  the  figure,  a,  medullary  cord 
of  dense  lymphoid  tissue;  b,  looser  lymphoid  tissue  of  the  cavernous  medulla;  c, 
capsule;  F,  dense  lymph  nodule  of  the  cortex;  HF,  fibrous  tissue  containing  the  large 
vessels  of  the  hilum;  s,  peripheral  lymphatic  sinus;  V,  blood-vessel.  Magnified 
several  diameters.  (After  Ranvier.) 

The  lymphoid  tissue  of  the  medulla  is  divisible  into  the  denser  branch- 
ing lymph  cords,  in  which  the  lymphocytes  are  closely  packed,  and  the 


FIG.  244. — TRANSECTION  OF  A  MESENTERIC  LYMPH  NODE  OF  A  MAX. 
Hematein  and  eosin.     Photo.     X  38. 

intervening  pulp  spaces,  in  which  lymphocytes  are  less  numerous,  and 
the  reticulum  of  which  is  continuous  with  that  of  the  cortical  nodules. 


238 


THE  LYMPHATIC  SYSTEM 


The  pulp  spaces  are  broad  channels,  which  are  occupied  by  a  reticu- 
lum  whose  meshes  are  partially  filled  with  lymphocytes.  They  are 
bounded  by  a  layer  of  endothelioid  cells  which  everywhere  incloses  the 
denser  lymph  cords.  The  function  of 
these  cords  would  seem  to  be  comparable 
to  that  of  the  peripheral  lymph  nodules. 

The  pulp  spaces  are  open  toward  the 
cortex,  whence  they  receive  the  afferent 
lymph  after  it  has  percolated  through  the 
nodules,  but  toward  the  hilum  the  spaces 
are  continued  into  the  efferent  radicles  of 
the  lymph  vessels  which,  in  the  connective 
tissue  of  this  part,  unite  into  larger 
trunks,  and  finally  form  several  efferent 
lymph  vessels  of  considerable  size. 

The  reticulum  of  the  lymph  gland  is 
a  close-meshed  network  of  interlacing  fi- 
brillar  bundles,  which  are  here  and  there 
clasped  by  flattened  endothelioid  connec- 
tive tissue  cells.  Eeticulum  is  but  poorly 
stained  with  either  acid  or  basic  dyes,  is 
destroyed  by  acids  and  bases,  but  is  not 
digested  by  pancreatin.  After  prolonged 
action  of  "Weigert's  specific  stain  for  elas- 
tic tissue  it  is  but  slightly  colored. 

Lymph  Cells.— The  great  majority  of 
these  cells  are  of  the  small  mononuclear 


FIG.  245. — DIAGRAM  OF  THE 
BLOOD-VESSELS  OF  A  LYMPH 
NODE. 

A  composite  section  of  three 
follicles  and  the  medullary  cords 
of  a  mesenteric  lymphatic  node 
of  the  dog.  A,  artery;  B,  medul- 
lary artery;  C,  follicular  vein;  E,  or  lymphocyte  type.  Large  mononuclear 

cells  with  a  considerable  cytoplasmic  body 
are  also  very  numerous.  Polymorphoim- 
clear  neutrophil  leukocytes,  though  of 
frequent  occurrence,  are  less  abundant 
than  the  previous  varieties.  Eosinophil 
cells  are  present  in  small  numbers,  and 
large  basophilic  mast-cells  are  occasionally  seen,  though  according  to 
Carlier  (Jour.  Anat.  and  Physiol.,  1893)  they  are  mostly  confined  to 
the  connective  tissue.  Drummond  (Jour.  Anat.  and  Physiol.,  1900) 
also  found  large  multinuclear  giant  cells,  megakaryocytes,  similar  to 
those  of  the  bone-marrow;  these  were,  however,  very  rare. 

Many  of  these  cells,  after  proper  fixation,  show  mitotic  figures.    This 


artery  going  to  the  capsule;  F, 
capillaries  in  the  periphery  of  a 
cord;  G,  medullary  vein;  //,  fol- 
licular artery;  7,  arterial  capil- 
laries in  a  follicle;  J,  vein  from 
capsule;  K,  cord;  L,  trabecula; 
F,vein.  X  601.  (After  Calvert.) 


HKMOLYMTH  NODES  239 

mitosis  has  been  most  frequently  observed  in  the  large  mononuclear  type, 
and  is  most  abundant  in  the  germinal  centers  of  the  nodules.  The 
small  mononuclear  and  polymorphonuclear  types  have  also  been  shown  to 
be  capable  of  cell  reproduction  by  indirect  division.  Reproduction  by 
direct  division  of  leukocytes  appears  to  be  rare,  if  indeed  it  ever  actually 
occurs. 

The  mononuclear  as  well  as  the  polymorphonuclear  forms  appear  to 
be  phagocytic.  Among  the  inclusions  which  have  been  found  within 
these  cells  are  fat  globules,  pigment  granules,  red  blood  corpuscles  in 
partial  disintegration,  insoluble  pigments,  such  as  carbon  granules,  etc., 
and  bacteria.  The  cells  of  the  reticulum  are  also  believed  to  be  phago- 
cytic. 

Blood-vessels.— The  arteries  enter  the  lymph  node  at  its  hilum,  and, 
following  the  trabecukie  within  which  they  lie,  are  distributed  to  all  por- 
tions of  the  organ.  In  the  medulla  branches  are  distributed  to  the 
lymph  cords,  in  which  they  form  a  wide-meshed  capillary  plexus. 

The  terminal  branches  of  the  primary  divisions  of  the  afferent  artery 
are  distributed  to  the  nodules  of  the  cortex.  A  single  nodular  branch 
(Calvert,  Anat.  Anz.,  1897)  enters  the  nodule  and  passes  straight  toward 
its  center,  where  it  breaks  into  a  plexus  of  divergent  capillaries  which 
unite  at  the  surface  of  the  nodule  to  form  small  venous  radicals. 

The  veins  follow  the  internodular  trabeculae  in  their  course  toward  the 
medulla,  where  they  enter  the  medullary  trabeculae,  are  augmented  by 
venous  radicals  from  the  capillary  plexuses  of  this  portion  of  the  gland, 
and  thence  follow  the  trabeculas  to  the  hilum,  where  they  unite  to  form 
the  efferent  vein. 

Certain  of  the  arteries  also  pass  from  the  medulla  through  the  inter- 
nodular  trabcculae  to  the  capsule  of  the  gland,  to  which  they  supply 
a  capillary  plexus.  The  blood  is  returned  through  veins  which  retrace 
the  course  of  the  arteries  and  enter  the  large  veins  of  the  medullary 
trabcculas.  The  spleen  contains  no  lymphatics  beyond  the  capsule. 

HEMOLYMPH  NODES 

(Hemal  Nodes) 

These  structures,  which  closely  resemble  the  lymph  nodes,  were  first 
described  by  IT.  Gibbes  (Quart.  Jour.  Mic.  Sc.),  in  1884.  He  found 
them  in  the  connective  tissue  between  the  renal  artery  and  vein,  in  the 
human  subject.  They  have  since  been  found  in  the  prevertebral  connec- 
tive tissue,  and  in  the  mediastinum  and  mesentery.  They  are  largej  and 
16 


240 


THE   LYMPHATIC    SYSTEM 


more  numerous  in  the  ruminants,  ox,  sheep,  etc.,  than  in  man.  Their 
size  varies  from  that  of  a  millet  seed  to  that  of  a  pea.  In  color  they 
closely  resemble  a  minute  extravasation  of  blood. 

These  organs  are  essentially  lymphatic  structures  in  which  the  lym- 
phoid  tissue  is  arranged  in  the  form  of  cords  rather  than  in  nodules.    The 


S.B.&. 


FIG.  246. — SECTION  OF  HUMAN  HEMOLYMPH  NODE  ("SPLENOLYMPH  GLAND"). 

C.,  capsule;  T.,  trabecula;  P.  B.  S.,  peripheral  blood  sinus;  L.  T.,  lymphoid  tissue, 
largely  in  the  form  of  cords;  S.  B.  S.,  secondary  blood  sinus;  H,  hilus.  (After 
Warthin.) 


node  is  inclosed  by  a  fibrous  capsule,  beneath  which  is  a  broad  sinus  filled 
with  blood.  In  this 'fact  lies  the  chief  distinguishing  feature  of  these 
glands. 

The  peripheral  Hood  sinus,  which  is  analogous  to  the  peripheral 
lymph  sinus  of  a  lymph  node,  sends  into  the  interior  of  the  organ  a 
greater  or  less  number  of  secondary  sinuses.  Based  largely  upon  the 
abundance  of  these  secondary  sinuses,  the  hemolymph  nodes  have  been 
divided  into  two  varieties,  named  by  Warthin  (Jour.  Bost.  Soc.  Mod, 
Sc.,  1901)  the  'splenolympli  glands'  and  the  'marrowlympli  glands' 


HEMOLYMPH  NODES 


241 


In  the  splenolymph  type,  which  is  the  more  abundant,  the  node 
is  of  small  size  and  is  well  filled  with  secondary  blood  sinuses.  The 
lymphoid  tissue  is  supported  by  a  similar  reticulum,  and  contains  the 
same  varieties  of  lymph  cells  as  in  the  lymph  nodes. 

In  the  marrowlymph  nodes  a  somewhat  similar  structure  is  found. 
The  blood  sinuses  are  less  numerous  and  lymph  nodules  do  not  occur 
(Vincent,  Warthin).  The  eosinophil  leukocytes  are  more  numerous 
than  in  the  splenolymph  type,  and  the  marrowlymph  nodes  as  a  rule  are 
the  larger. 

Huntington   (Amer.  Jour.  Anat,  16,  3,  1914)   has  suggested  that 


FIG.  247. — HORIZONTAL  SECTION  THROUGH  THE  FAUCIAL  TONSIL  OF  A  CHILD. 

Semi-diagrammatic,    a,  stratified  epithelium;  b,  crypts;  c,  lymph  nodule;  d,  mucus- 
secreting  gland.    Hematein  and  eosin.    X  about  20. 


some  of  the  structures  described  as  hemolymph  nodes  may  be  post-natal 
hemopoietic  foci,  in  which  erythrocytes  develop  from  the  endothelium 
of  the  lymph  channels.  They  probably  function  as  accessory  spleens  hav- 
ing a  combined  lymphopoietic  and  phagocytic  activity. 

Intermediate  types  between  the  lymph  nodes  and  the  splenolymph 
type  (Vincent,  Jour.  Anat.  and  Physiol.,  1897)  on  the  one  hand,  and  be- 
tween the  splenolymph  node  and  the  spleen  and  marrowlymph  type  on 
the  other  hand,  are  of  frequent  occurrence. 

Blood  Supply. — The  afferent  artery,  according  to  Drummond  (Jour. 
Anat.  and  Physiol.,  1900),  enters  the  hilum  with  the  connective  tissue, 
and  through  the  trabecula?  reaches  all  parts  of  the  node.  In  the  lymphoid 


242  THE  LYMPHATIC  SYSTEM 

tissue  its  branches  form  a  capillary  plexus  whose  vessels  open  into  the 
blood  sinuses.  All  the  sinuses,  peripheral  and  secondary,  communicate 
with  each  other,  and  from  them  the  blood  is  ultimately  collected  into 
two  or  more  thin-walled  veins.  In  the  center  of  the  gland  these  vessels 
unite  to  form  an  efferent  vein  which  passes  out  at  the  hilum. 


DEVELOPMENT  OF  LYMPH  NODES 

Lymph  nodes  arise  through  the  invasion  of  primary  lymphatic  capillary 
plexuses  by  lymphocytes.  The  first  lymph  nodes  arise  in  the  regions  of  the 
axilla  and  groin  during  the  third  month  of  development.  Such  areas  be- 
come circumscribed  by  the  development  of  a  capsule  from  the  surrounding 
mesenchyma.  The  capsular  tissue  is  continued  into  the  developing  node 
in  the  form  of  trabeculse,  terminating  in  a  dense  network  of  delicate  reticu- 
lar  fibers.  Hydrostatic  conditions  probably  determine  the  formation  of  a 
peripheral  lymph  sinus.  The  retention  of  certain  channels  (internodular 
and.  medullary  sinuses)  between  the  peripheral  sinus  and  the  efferent  lym- 
phatics at  the  hilum  is  likewise  probably  determined  mainly  by  the  opera- 
tion of  like  factors,  brought  into  play  through  the  appearance  of  cortical 
nodules.  These  nodules  arise  as  regions  of  proliferative  activity  of  lympho- 
cytes. The  node  has  meanwhile  early  become  invaded  at  a  point  which 
becomes  the  hilum  by  a  vascular  and  nerve  supply.  Nodules  arise  as  ac- 
cumulations of  proliferating  lymphocytes  about  the  cortical  arterial  twigs. 
Hemolymph  nodes  apparently  arise  in  a  manner  similar  to  the  origin  of 
ordinary  lymph  nodes,  and  become  only  secondarily  modified.  The  reticu- 
lar  tissue  of  lymph  nodes  may  in  part  arise  from  the  capillary  endotbelium. 

The  function  of  lymph  nodes  is  the  production  of  lymphocytes,  which 
become  phagocytic  leukocytes.  Besides  having  a  leukopoietic  role,  lymph 
nodes  probably  function  also  as  centers  for  the  dissolution  of  worn-out 
blood  elements,  in  which  process  phagocytosis  predominates,  the  lympho- 
cytes being  in  part  assisted  by  the  endothelial  cells  of  the  capillaries. 
Lympboid  aggregations  also  serve  as  'lymph  filters,'  the  phagocytes  removing 
from  the  lymph  bacteria  and  other  noxious  products. 


THE  TONSILS 

The  Faucial  Tonsils  (Palatine  Tonsils;  Amygdala)  .—The  tonsils 
consist  of  a  mass  of  lymphoid  tissue  which  projects  slightly  from  either 
side  into  the  cavity  of  the  fauces,  and  is  covered  by  a  layer  of  stratified 
epithelium  continuous  with  that  which  lines  the  oral  and  pharyngeal 


THE  TONSILS 


243 


cavities.  The  lymph  nodules  which  compose  the  tonsil  immediately 
underlie  the  epithelial  coat,  and  are  embedded  in  areolar  connective 
tissue. 

The  epithelial  coat  here  and  there  penetrates  the  substance  of  the 
organ  in  the  form  of  invaginated  funnel-shaped  depressions,  the  crypts 
('follicles'  of  the  tonsils).  The  direction  of  the  crypts  in  the  upper  third 
of  the  tonsil  is  downward  and  outward  (C.  P.  Johnson).  The  ducts  of 
many  mucous  glands  open  into  the  recesses  of  these  branching  crypts. 
The  mucus-secreting  glands  lie  in  the  loose  connective  tissue  which  sur- 


£s&!i^<**i  *«*^  *  ^  ®    •*  *•*  -.*»* ' 

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° 


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FIG.  248. — FROM  A  CRYPT  OF  A  DOG'S  TONSIL. 

a,  stratified  epithelium ;  b,  basal  margin  of  the  epithelium ;  c,  infiltration  of  the  epi- 
thelium by  leukocytes;  d,  spaces  in  the  epithelium  filled  with  leukocytes  and  epithelial 
cells;  e,  blood-vessel;  /,  lymphoid  tissue.  X  150.  (After  Bohm  and  von  Davidoff .) 

rounds  the  tonsil  on  all  but  its  faucial  surface.  The  crypts  are  lined 
throughout  by  a  layer  of  stratified  epithelium,  which  is  continuous  with 
that  on  the  free  surface  of  the  tonsil,  but  which  becomes  progressively 
thinner  as  it  recedes  into  the  deeper  recesses  of  the  crypts. 

Many  of  the  lymph  cells  migrate  into  the  intercellular  spaces  of  the 
epithelial  layer,  and  even  penetrate  to  the  free  surface;  thus  they  find 
their  way  into  the  oral  cavity,  where  they  are  found  in  large  numbers 
in  the  saliva,  as  'salivary  corpuscles'  "If  such  salivary  corpuscles  are  ex- 
amined in  a  drop  of  saliva,  freshly  prepared,  the  fine  intracellular  gran- 
ules of  the  polymorphonuclear  leukocytes  will  be  seen  to  undergo  an 
active  dancing  movement,  Brownian  motion.  The  salivary  corpuscles  are 
derived  not  only  from  the  faucial  tonsils  but  from  the  other  lymphoid 
tissue  which  is  in  relation  with  the  oral  mucous  membrane,  e.g.,  the 
lingual  and  pharyngeal  tonsils. 

The  passage  of  leukocytes  through  the  epithelial  surface  of  the  fauejal 


244 


THE  LYMPHATIC  SYSTEM 


tonsil  is  so  very  active  that  at  times  the  epithelium  becomes  completely 
filled  with  these  cells,  and  it  is  then  difficult  to  distinguish  it  from  the 
adenoid  tissue  beneath.  The  normal  tonsils  atrophy  after  puberty. 

The  Lingual  Tonsil. — A  collection  of  lymph  nodules  is  also  found 
at  the  base  of  the  tongue  in  the  median  line,  between  the  circumvallate 
papillae  and  the  epiglottis.  This,  because  of  its  similarity  in  appearance 
and  in  structure  to  the  faucial  tonsil,  is  called  the  lingual  tonsil. 

In  the  lingual  tonsil,  however,  the  nodules  are  grouped  about  a 


FIG.  249. — THE  LINGUAL  TONSIL  OF  MAN. 
a,  a  crypt;  b,  von  Ebner's  glands.    Hematein  and  eosin.     X  45. 

single  wide-mouthed  crypt,  the  foramen  ccecum  lingui.  This  crypt  is 
frequently  branched,  and  into  it  the  many  mucous  glands  of  the  neighbor- 
ing lingual  mucosa  pour  their  secretion. 

The  Pharyngeal  Tonsil.— The  posterior  wall  of  the  nasopharynx  is 
supplied  with  a  similar  accumulation  of  lymph  nodules,  the  pharyngeal 
tonsil.  It  lies  in  the  median  line  and  extends  downward  from  between 
the  orifices  of  the  auditory  (Eustachian)-  tubes  for  a  distance  of  three 
centimeters  (Klein).  It  contains  a  considerable  number  of  lymph  nod- 
ules and  several  small  crypts.  The  lateral  extensions  in  the  vicinity 
of  the  tubal  orifices  are  sometimes  known  as  the  tubal  tonsils. 

The  pharyngeal  tonsil  is  prone  to  hypertrophy  in  youth,  in  which 


THE  SPLEEN  245 

case  it  forms  the  adenoid  growths  which  are  so  common  in  strumous 
children. 

Viewing  the  several  tonsils  and  the  associated  lymphoid  tissue  as  a 
whole,  it  will  be  perceived  that  they  constitute  a  lymphoid  ring  at  the 
gateway  to  the  alimentary  and  respiratory  tracts.  The  function  of  the 
lymphoid  tissue  is  to  produce  phagocytic  leukocytes  for  the  protection  of 
the  body  against  bacteria  and  other  noxious  products.  The  tonsillar  crypts 
offer  favorable  foci  for  the  lodgment,  invasion  and  attack  of  such  harmful 
elements.  The  location  of  this  annular  mass  of  lymphoid  tissue  is  signifi- 
cant; it  is  placed  where  it  can  apparently  best  perform  a  necessary  func- 
tion. When  called  upon  to  increase  its  functional  activity  lymphoid  tissue 
responds  by  hypertrophy;  this  of  itself  may  cause  inconvenience  by  ob- 
structing the  channels  employed  in  respiration  and  phonation.  But  when 
unable  to  respond  adequately  and  thus  successfully  cope  with  the  infecting 
material,  the  tonsils  become  diseased.  This  is  commonly  considered  to  call 
for  removal  of  the  involved  lymphoid  masses.  But  it  would  seem  that  the 
excision  of  the  tonsils  would  result  in  handicapping  the  organism  in  its 
perpetual  combat  with  bacteria,  by  depriving  it  of  a  means  of  defense; 
moreover  in  the  case  of  removal  of  the  faucial  tonsils,  proper  phonation  may 
also  be  interfered  with.  However,  excised  tonsillar  tissue  is  probably 
largely  compensated  for  by  regeneration  and  hypertrophy  of  other  non- 
involved  lymphoid  tissue.  Nevertheless  it  has  been  suggested  that  much 
could  be  gained  through  prophylactic  means  consisting  largely  perhaps  in 
the  promotion  of  nose  breathing  and  the  prevention  of  chronic  nasal  cold 
in  infants. 

THE  SPLEEN 

Structure. — The  spleen  is  the  largest  lymphoid  organ  of  the  body. 
It  is  located  to  the  left  and  dorsally  between  the  stomach  and  diaphragm, 
has  an  irregular  oval  outline,  measures  about  five  inches  in  length  and 
three  inches  in  thickness,  and  weighs  about  seven  ounces.  It  is  subject 
to  great  variations  in  size  and  shape.  It  is  enveloped  by  a  thick  fibro- 
elastic  capsule,  or  tunica  albuginea,  containing  smooth  muscle  in  its 
inner  portion.  External  to  this  is  also  a  peritoneal  investment,  or  tunica 
serosa.  The  capsule  of  the  spleen  of  the  ox  is  especially  robust,  and 
rich  in  smooth  muscle.  At  one  point,  the  liilum,  the  capsule  projects 
into  the  spleen  as  a  large  mass  of  trabecular  tissue.  Over  the  entire 
surface  also  other  trabeculae  project  from  the  capsule  into  the  paren- 
chyma of  the  organ.  These  trabeculae  are  of  similar  structure  to  the 
capsule.  The  supporting  tissue  of  the  parenchyma  is  a  delicate  reticu- 


246  THE   LYMPHATIC   SYSTEM 

lum.    This  is  continuous  with  the  fibre-elastic  terminal  processes  of  the 
fibromuscular  trabeculae. 

The  primary  trabeculre  divide  the  parenchyma  imperfectly  into 
roughly  pyramidal  compartments  about  one  millimeter  in  diameter,  with 
three  trabecula?  for  each  lobule.  This  lobulatiori  is  faintly  indicated  by 
surface  markings.  According  to  Mall  this  unit  of  structure,  the  splenic 
lobule,  is  further  subdivided  into  about  ten  smaller  compartments  by 


FIG.  250. — PORTION  OF  SPLEEN  OF  CAT,  SHOWING  CAPSULE  (ABOVE  AND  AT 

LEFT)  AND  FIVE  SPLENIC  NODULES. 

Between  the  nodules  can  be  seen  vascular  trabecute  continuous  with  the  capsule 

X60. 

anastomosing  septa,  continuous  with  the  primary  trabeculse.  The  divi- 
sion of  the  spleen  into  lobules,  and  their  subdivision  into  lobular  com- 
partments has  structural  significance  also  from  the  viewpoint  of  the 
blood  supply.  A  knowledge  of  the  microscopic  structure  of  the  spleen 
is  dependent  upon  an  understanding  of  the  distribution  of  the  blood- 
vessels. 

Blood-vessels. — The  splenic  artery  enters  at  the  hilum,  associated 
with  the  splenic  vein.  The  larger  arterial  branches  are  located  within 
the  coarser  trabeculae  continuous  with  the  connective  tissue  of  the  hilum 
and  still  accompanied  by  the  larger  tributaries  of  the  splenic  vein.  The 


THE  SPLEEN 


247 


smaller  arteries  part  company  with  the  veins  when  they  leave  the  tra- 
becula? and  pass  into  the  apices  of  the  lobules.  At  the  point  of  entrance 
into  the  lobule  the  adventitia  of  the  intralobular  artery  becomes  in- 
filtrated with  lymphocytes,  forming  thus  a  spherical  or  fusiform 
iymphoid  mass, 
the  splenic  nodule 
(Malpighian  cor 
puscle)  character- 
istic of  the  spleen. 
This  arterial  ves- 
sel gives  off  nu- 
merous branches 
to  the  splenic 
nodule,  some  of 
which  pass  beyond 
the  confines  of  the 
nodule  into  the 
splenic  pulp. 
Some  of  these 
nodules  contain 
germ  centers.  In 
infancy  all  of  the 
nodules  are  said 
to  contain  germ 
centers. 

The  artery 
usually  passes 
excentri  cally 
through  the  nod- 
ule. The  nod- 
ules are  fre- 
quently situated 

at  the  point  where  the  artery  branches  and  in  consequence  contain  two 
arterial  vessels.  Beyond  the  splenic  nodules,  the  intralobular  artery 
breaks  into  a  number  of  twigs,  one  for  each  lobular  compartment.  Within 
each  compartment,  the  arteriole  divides  into  a  brush  of  delicate  precapil- 
lary  arterioles,  the  penicilli  of  Euysch.  On  these  appear  an  ellipsoidal 
condensation  of  reticular  tissue  forming  the  so-called  splenic  ellipsoids. 
These  arterioles  (six  to  ten  microns  in  diameter)  are  known  as  sheathed 
arteries.  The  splenic  pulp  of  the  lobules  can  be  divided  into  somewhat 


FIG.  251. — DIAGRAM  OP  A  LOBULE  OF  THE  SPLEEN. 

A,  artery  lying  in  the  center  of  the  lobule;  Am,  a  terminal 
ampulla  of  the  artery;  C,  intralobular  vein;  L,  a  splenic  cor- 
puscle; P,  venous  plexus  within  the  pulp  of  the  spleen;  Tr, 
fibromuscular  trabecula  within  the  lobule;  V,  interlobular 
vein,  lying  in  a  large  trabecula.  (After  Mall.) 


248 


THE  LYMPHATIC  SYSTEM 


denser  cords  of  uncertain  outline,  the  splenic  pulp  cords,  and  slightly 
looser  intercordal  pulp,  the  venous  sinuses,  corresponding  to  the  sinuses 
of  the  medulla  of  lymph  nodes.  The  penicilli  are  located  in  the  pulp 
cords.  Terminally  these  penicilli  expand  into  dilatations,  the  ampulla 
of  Thoma. 

The  exact  method  of  passage  of  the  blood  from  the  terminal  arterioles 
to  the  initial  venules  is  uncertain  and  disputed.  It  is  certain  only  that 
blood  passes  freely  at  this  point  into  the  splenic  pulp.  This  gives  the 
adenoid  tissue  a  deeply  red  or  purple  color,  in  contrast  to  the  light  pink 
color  of  ordinary  lymph  nodes,  due  to  the  presence  of  innumerable  ery- 

throplastids.     It   seems  prob- 
A 
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VEIN  IN  THE 


able  that  the  walls  of  the  con- 
necting  capillaries  and  the  ini- 
tial  venules  (cavernous  veins, 
venous  sinuses)  are  fenestra- 
ted,  permitting  the  free  pas- 
sage of  blood  from  these  vessels 
into  the  spleen  pulp. 

According  to  some  au- 
thorities the  blood  passes 
by  two  routes  from  the 
arterioles  to  the  venules; 
(1)  through  the  arterial 
ampulla?  directly  into  the 
venules  (venous  ampullae)  ; 
and  (2)  from  other  ter- 
minal arterial  twigs  into 
the  spleen  pulp,  from  where  it  is  collected  by  the  venules. 

The  veins  thus  begin  as  wide  sinusoidal  channels  (pulp  veins)  within 
the  splenic  pulp.  At  first,  and  for  a  considerable  dfstance,  they  follow 
an  independent  course  through  the  pulp,  receiving  at  the  same  time 
frequent  accessions  of  blood  from  other  venous  radicals.  Finally,  how- 
ever, the  veins  enter  the  larger  trabeculae,  but  are  still  devoid  of  more 
complete  coats  than  the  thin  membrane  of  fibre-elastic  tissue  which  sur- 
rounds the  endothelial  tube,  but  which  is  now  ensheathed  by  the  trabecu- 
lar  tissue.  Henceforth  the  path  of  the  veins  lies  within  the  trabeculse 
(interlobular  veins),  and  is  directed  toward  the  hilum.  On  approaching 
the  hilum  the  larger  veins  acquire  the  usual  venous  coats.  Having  ar- 
rived at  the  hilum,  they  form  several  efferent  vessels  which,  in  the  out- 
lying connective  tissue,  form  by  their  union  the  splenic  vein. 


FIG.  252.  —  THE  ORIGIN  OF  A 
SPLENIC  PULP. 

a,  venous  endothelium  ;  b,  leukocytes;  c, 
red  blood  corpuscles  (appearing  rather  too 
dark  in  the  reproduction);  d,  a  mesh  of  the 
splenic  pulp.  Highly  magnified.  (After 
Bannwarth.) 


THE  SPLEEN 


249 


Differentiation  of  Spleen  from  Lymph  Node.— The  spleen  in  sec- 
tion can  be  readily  differentiated  from  a  lymph  node :  it  lacks  a  definite 
subdivision  into  cortex  and  medulla  characteristic  of  the  lymph  node,  its 
pulp  contains  a  preponderating  number  of  red  blood  corpuscles,  and  its 
capsule  is  relatively  very  robust  and  contains  a  greater  amount  of  smooth 
muscle.  The  spleen  may  be  thought  of  as  a  congested  lymph  node,  con- 
sisting wholly  of  medulla,  throughout  which  are  scattered  lymph  nodules, 
the  splenic  nodules.  It  might  quite  properly  be  described  as  a  huge  hemo- 
lymph  node. 

Splenic  Cells.— Besides  erythroplastids  and  occasional  erythrocytes, 
the  pulp  contains  also  the 
several  varieties  of  leuko- 
cytes: lymphocytes,  granu- 
locytes,  a  few  megakaryo- 
cytes,  and  blood-platelets. 
The  leukocytes  of  the  spleen 
are  largely  of  the  large 
monoimclear  type.  These 
are  notably  phagocytic,  fre- 
quently containing  erythro- 
plastids, fragments  of  cells, 
pigment  and  other  granular 
debris.  They  are  in  a  sense 
specific  for  the  spleen,  hence 
called  splenic  cells.  Mega- 
karyocytes  are  abundant  in  FlG  253.— TYPES  OF  CELLS  FROM  A  SMEAR  PREP- 
the  fetal  spleen  during  its  ARATION  OF  THE  PULP  OF  THE  HUMAN  SPLEEN. 
period  of  erythropoietic  a,  lymphocytes;  b,  polymorphonuclear  neutro- 
function,  but  rare  in  the  Phil  leukocytes  whose  granules  are  not  stained 
arli  It  nl  ky  the  method  used;  c,  large  mononuclear  leuko- 

cyte; d,  eosinophil  cells;  e,  basophil  cell;  /,  red 

Lymph  Supply.  —  The  blood  corpuscles.  Hematein  and  eosin.  X  1200. 
lymph  supply  of  the  spleen 

is  relatively  scanty.  The  capsular  is  independent  of  the  parenchymal 
system,  which  latter  consists  chiefly  of  peri  vascular  lymph  spaces  and 
vessels  draining  toward  the  hilum. 

Nerve  Supply. — The  innervation  includes  both  medullated  and  non- 
medullated  fibers.  The  latter  predominate,  and  are  distributed  to  the 
smooth  muscle  of  the  capsule,  trabeculae,  and  blood-vessels. 

Functions. — The  spleen  functions  as  a  leukopoietic  organ  and  as  a 
blood  filter.  This  is  indicated  both  by  the  direct  evidence  of  lymphocyte 


,--- 


250  THE  LYMPHATIC  SYSTEM 

proliferation  and  the  ingestion  of  erythroplastid  debris  by  the  splenic 
and  endothelial  cells,  and  by  the  fact  that  the  proportion  of  lymphocytes 
to  erythroplastids  in  the  splenic  vein  is  very  much  greater  than  in  the 
splenic  artery.  After  severe  hemorrhage  or  certain  anemias  the  spleen 
may  resume  its  fetal  erythropoietic  function.  Numerous  small  super- 
numerary spleens,  of  varying  size  but  usually  about  the  size  of  a  pea, 
are  frequently  found  in  the  vicinity  of  the  spleen. 

Besides  the  production  of  lymphocytes  and  the  destruction  of  senile 
red  corpuscles,  the  normal  adult  spleen  has  been  credited  also  with  an  eryth- 
ropoietic role,  and  with  a  function  concerned  with  the  metabolism  of  iron. 
That  the  spleen  does  not,  however,  have  any  specific  function  absolutely 
essential  to  life  is  proved  by  the  fact  that  it  may  be  removed  without 
serious  consequence.  Obviously  its  function  may  be  taken  over  by  some 
other  organs.  Such  compensatory  role  is  usually  attributed  to  the  hemo- 
lymph  nodes  and  the  red  marrow.  However,  splenectomy  in  dogs  is  not 
followed  by  increase  in  the  number  or  size  of  the  hemolymph  nodes,  nor  by 
a  production  of  accessory  spleens  (Meyer,  Jour.  Exp.  Zool.,  16,  2,  1914). 
Removal  of  the  spleen  in  dogs  seems  to  exert  a  stimulating  effect  upon  the 
formation  of  red  cells  in  bone-marrow  (Krumbhaar  and  Musser,  Jour.  Exp. 
Med.,  20,  2, 1914).  Pearse  and  Pepper  (Jour.  Exp.  Med.,  20,  1,  1914)  found 
that  splenectomy  caused  a  transformation  of  yellow  into  red  marrow.  The 
result  is  interpreted  as  showing  that  in  the  absence  of  the  spleen  the  mar- 
row may  take  on  the  function  of  storing  and  elaborating  the  iron  of  the 
blood  pigment  for  future  utilization  by  new  red  cells.  The  experiments 
of  Austin  and  Pearse  (Jowr.  Exp.  Med.,  20,  2,  1914)  on  the  contrary  lead 
them  to  conclude  that  the  spleen  does  not  exert  a  constant  and  important 
function  on  iron  metabolism.  The  complete  function  of  the  spleen  appar- 
ently remains  largely  unknown.  Like  the  thymus  it  is  sometimes  classified 
among  the  organs  of  internal  secretion. 

Development. — The  anlage  of  the  spleen  appears  at  the  beginning  of 
the  second  month  as  a  condensation  and  swelling  in  the  mesenchyma  on 
the  left  border  of  the  dorsal  mesogastrium.  The  overlying  mesothelium 
proliferates  extensively  and  its  cells  invade  the  mesenchyma  obliterating 
the  line  of  demarcation.  The  early  histogenesis  is  obscure.  The  mesen- 
chyma is  potentially  capable  of  producing  all  the  definitive  elements  of  the 
spleen :  connective  tissue  capsule  and  framework,  and  lymphocytes.  The 
mesothelium,  genetically  closely  related  to  mesenchyma,  probably  aids  in 
the  general  process.  Probably  also  the  bulk  of  the  later  lymphocytes  invade 
the  spleen  from  without. 


CHAPTER   X 
MUCOUS    MEMBRANES— GLANDS 

The  histologic  structures  which  are  necessary  for  the  formation  of 
a  secretion  include  an  epithelial  surface,  and  a  tunica  propria  of  con- 
nective tissue  which  supports  the  requisite  blood  and  lymphatic  vessels 
and  the  controlling  nerve  supply.  These  structures  may  either  form 
smooth  membranous  surfaces  or  apparent  epithelial  invaginations.  The 
former  are  found  on  the  surface  of  the  mucous  membranes,  the  latter 
are  the  secreting  glands. 


MUCOUS  MEMBRANES 

The  mucous  membranes  may  be  said  to  include  all  those  secreting 
surfaces  which  are  directly  or  indirectly  connected  with  the  surface  of 
the  body,  hence  their  epithelial  clothing  is  continuous  with  that  of  the 
skin.  The  mucous  membranes  form  the  lining  coat  of  the  respiratory 
and  alimentary  systems,  together  with  the  ducts  of  their  secreting  glands ; 
in  the  nose  this  membrane  is  continuous  through  the  tear  ducts  with 
the  conjunctiva  of  the  eye  and  through  the  auditory  (Eustachian)  tubes 
with  the  lining  membrane  of  the  middle  ear.  The  broad  expanse  thus 
formed  is  known  as  the  gastro pneumonic  mucous  membrane.  A  second 
membranous  sheet,  the  genito-urinary  mucous  membrane,  clothes  the 
organs  of  the  genital  and  urinary  systems;  it  thus  forms  the  lining  mem- 
brane of  the  vagina,  uterus,  and  Fallopian  tubes,  of  the  urethra,  bladder, 
ureters  and  pelvis  of  the  kidney,  of  the  ducts  and  tubules  of  the  prostate 
gland,  the  testis,  and  the  smaller  secreting  glands  which  are  connected 
with  the  genital  system. 

A  mucous  membrane  consists  of  a  superficial  layer  of  epithelium 
of  varying  type,  which  rests  upon  a  basement  membrane  (membrana 
propria)  and  is  in  turn  supported  by  an  investment  of  connective  tissue, 
the  tunica  propria,  or  corium.  The  tunica  propria  is  richly  supplied 
with  small  blood-vessels  and  lymphatics;  its  nerve  fibrils  are  n*ot  only 
distributed  to  the  walls  of  the  blood-vessels  but  in  many  cases  send  ter- 

251 


254  MUCOUS  MEMBRANES— GLANDS 


HISTOLOGIC    TYPES    OF    GLANDS: 

1.  Simple. 

2.  Convoluted. 


I.  Tubular  J 


3.  Branched. 

4.  Compound. 

5.  Compound  tubulo-acinar    (alveolar)  ;  racemose. 


1.  Simple. 
II.  Saccular 

,  J    2.  Branched, 
(alveolar)  |  , 

3.  Compound. 

III.  Ductless  glands;  endocrine  glands. 

Glands  of  the  tubular  and  saccular  types  contain  an  actively  secreting 
portion  or  fundus  and  a  duct.  Such  externally  secreting  glands  are  also 
known  as  'exocrine'  glands.  In  the  ductless  ('endocrine')  glands  the 
duct  is  absent.  The  duct,  though  its  epithelium  may  take  some  part 
in  the  formation  of  the  glandular  secretion,  primarily  serves  to  convey 
the  secretion  of  the  fundus  to  the  free  surface  of  the  mucous  membrane. 

The  epithelium  of  the  duct,  as  a  rule,  more  or  less  closely  resembles 
that  of  the  mucous  membrane  upon  whose  surface  it  opens.  The  epi- 
thelium of  the  fundus,  on  the  other  hand,  usually  differs  from  that  of 
the  duct  and  varies  according  to  the  nature  of  its  secretion.  In  many  of 
the  glands  the  epithelium  is  typically  mucus  secreting;  others  produce 
a  clearer,  watery,  and  less  viscid,  serous  secretion.  Hence  it  is  possible 
to  distinguish  the  following 

PHYSIOLOGIC   TYPES  OF  GJ-ANDS  I 

I.  Serous  glands. 

II.  Mucous  glands. 

III.  Glands  which   are  both   mucous  and  serous    (mixed  glands). 

IV.  Glands   which   are   neither   mucous   nor   serous. 

This  physiologic  classification  is  not  in  any  way  the  equivalent  of 
the  histologic  gland  types  mentioned  above.  Thus  both  serous  and 
mucous  glands,  in  different  locations,  form  almost  every  variety  of 
tubular  gland. 

DESCRIPTION  OF  PHYSIOLOGIC  TYPES 

The  glands  of  the  fourth  type  arc  too  varied  in  their  structure 
to  be  considered  collectively  to  advantage.  The  reader  is  referred  to 


GLANDS 


255 


the  several  chapters  in  which  they  are  described  in  detail.  This  type 
includes  the  testis,  the  prostate,  the  ccrumiuous  glands,  many  of  the 
ductless  glands,  and  also  some  authors  describe  the  ovary  and  the  lungs 
as  conforming- to  the  glandular  type  of  structure. 

The  mixed  glands  include  some  tubules  which  are  characteristically 
mucous,  while  others  are  typical  serous  secreting.  Occasionally  both 
types  of  secreting  cells  are  contained  within  the  same  tubule. 

Mucus-secreting  cells  possess  the  general  .characteristics  which 
have  been  previously  recited  4 

under  the  head  of  goblet  cells 
(Chapter  II ).  When  void  of 
secretion  the  cytoplasm  of 
mucous  cells  is  granular, 
their  nucleus  centrally  situ- 
ated, and  their  shape  more  or  jf^\^  -  ^ 
less  columnar.  The  pre-secre-  Iff  -  ff\ 

tion  ^accumulates  in  the  cen- 
tral portion  of  the  cell  and 
occupies  an  area,  adjacent  to 
the  glandular  lumen,  which 
steadily  increases  in  size  until 
the  greater  part  of  the  cyto- 
plasm has  been  replaced;  the 
nucleus  is  pushed  to  the  proxi- 
mal or  attached  end  of  the  cell ; 
and  the  whole  cell  often  be- 
comes swollen  and  distended  to  more  than  double  its  original  size.  Finally 
the  cell  membrane  ruptures  and  the  mucus  pours  out  upon  the  free  sur- 
face of  the  membrane. 

At  the  base  of  the  mucus-secreting  cells,  and  between  them  and 
their  basement  membrane,  are  groups  of  epithelial  cells  having  a  finely 
granular  cytoplasm,  which  form  crescentic  cell  masses,  the  demilunes 
of  Heidenhain  (crescents  of  Gianuzzi).  In  the  tubules  of  some  glands 
these  demilunes  are  extremely  minute,  in  others  they  occupy  a  con- 
siderable portion  of  the  epithelial  coat  and  encroach  upon  the  glandular 
lumen.  Their  significance  is  not  definitely  understood.  They  have 
been  considered  as  representing  either  secreting  cells  which  are  in  a 
state  of  rest  following  the  discharge  of  their  secretion,  or  as  primordial 
cells  which  by  reproduction  give  origin  to  true  mucus-secreting  cells. 
It  is  quite  possible  that  both  of  these  functions  are  assumed  by  the  several 


FIG.  256. — TRANSECTION  OF  THREE  SECRETING 
TUBULES  OF  THE  SUBMAXILLARY  GLAND  OF 
MAN. 
A,  a  serous  tubule;  B,  a  mucous  tubule;  C, 

a  mucous  tubule  with  a  demilune,  d.  Hematein 

and  eosin.     X  665. 


MUCOUS  MEMBEANES— GLANDS 


HISTOLOGIC    TYPES    OF    GLANDS: 

1.  Simple. 

2.  Convoluted. 
I.  Tubular  4    3.  Branched. 

4.  Compound. 

5.  Compound  tubulo-acinar   (alveolar)  ;  racemose. 

1.  Simple. 
II.  Saccular  ,     , 

.  .    2.  Branched, 
(alveolar)  1 

3.  Compound. 

III.  Ductless  glands;  endocrine  glands. 

Glands  of  the  tubular  and  saccular  types  contain  an  actively  secreting 
portion  or  fundus  and  a  duct.  Such  externally  secreting  glands  are  also 
known  as  'exocrine'  glands..  In  the  ductless  ('endocrine')  glands  the 
duct  is  absent.  The  duct,  though  its  epithelium  may  take  some  part 
in  the  formation  of  the  glandular  secretion,  primarily  serves  to  convey 
the  secretion  of  the  fundus  to  the  free  surface  of  the  mucous  membrane. 

The  epithelium  of  the  duct,  as  a  rule,  more  or  less  closely  resembles 
that  of  the  mucous  membrane  upon  whose  surface  it  opens.  The  epi- 
thelium of  the  fundus,  on  the  other  hand,  usually  differs  from  that  of 
the  duct  and  varies  according  to  the  nature  of  its  secretion.  In  many  of 
the  glands  the  epithelium  is  typically  mucus  secreting;  others  produce 
a  clearer,  watery,  and  less  viscid,  serous  secretion.  Hence  it  is  possible 
to  distinguish  the  following 

PHYSIOLOGIC  TYPES   OF  GIANDS  : 

I.  Serous  glands. 
II.  Mucous  glands. 

III.  Glands  which   are   both   mucous  and  serous    (mixed  glands). 

IV.  Glands   which   are   neither   mucous   nor   serous. 

This  physiologic  classification  is  not  in  any  way  the  equivalent  of 
the  histologic  gland  types  mentioned  above.  Thus  both  serous  and 
mucous  glands,  in  different  locations,  form  almost  every  variety  of 
tubular  gland. 

DESCRIPTION  OF  PHYSIOLOGIC  TYPES 

The  glands  of  the  fourth  type  are  too  varied  in  their  structure 
to  be  considered  collectively  to  advantage.  The  reader  is  referred  to 


GLANDS 


255 


the  several  chapters  in  which  they  are  described  in  detail.  This  type 
includes  the  testis,  the  prostate,  the  cerumiuous  glands,  many  of  the 
ductless  glands,  and  also  some  authors  describe  the  ovary  and  the  lungs 
as  comforniing- to  the  glandular  type  of  structure. 

The  mixed  glands  include  some  tubules  which  are  characteristically 
mucous,  while  others  are  typical  serous  secreting.  Occasionally  both 
types  of  secreting  cells  are  contained  within  the  same  tubule. 

Mucus-secreting  cells  possess  the  general  .characteristics  which 
have  been  previously  recited 
under  the  head  of  goblet  cells 
(Chapter  II).  When  void  of 
secretion  the  cytoplasm  of 
mucous  cells  is  granular, 
their  nucleus  centrally  situ- 
ated, and  their  shape  more  or 
less  columnar.  The  pre-secre- 
tion  ^accumulates  in  the  cen- 
tral portion  of  the  cell  and 
occupies  an  area,  adjacent  to 
the  glandular  lumen,  which 
steadily  increases  in  size  until 
the  greater  part  of  the  cyto- 
plasm has  been  replaced;  the 
nucleus  is  pushed  to  the  proxi- 
mal or  attached  end  of  the  cell ; 
and  the  whole  cell  often  be- 
comes swollen  and  distended  to  more  than  double  its  original  size.  Finally 
the  cell  membrane  ruptures  and  the  mucus  pours  out  upon  the  free  sur- 
face of  the  membrane. 

At  the  base  of  the  mucus-secreting  cells,  and  between  them  and 
their  basement  membrane,  are  groups  of  epithelial  cells  having  a  finely 
granular  cytoplasm,  which  form  crescentic  cell  masses,  the  demilunes 
of  Heidenhain  (crescents  of  Gianuzzi).  In  the  tubules  of  some  glands 
these  demilunes  are  extremely  minute,  in  others  they  occupy  a  con- 
siderable portion  of  the  epithelial  coat  and  encroach  upon  the  glandular 
lumen.  Their  significance  is  not  definitely  understood.  They  have 
been  considered  as  representing  either  secreting  cells  which  are  in  a 
state  of  rest  following  the  discharge  of  their  secretion,  or  as  primordial 
cells  which  by  reproduction  give  origin  to  tnie  mucus-secreting  cells. 
It  is  quite  possible  that  both  of  these  functions  are  assumed  by  the  several 


FIG.  256. — TRANSECTION  OF  THREE  SECRETING 
TUBULES  OF  THE  SUBMAXILLARY  GLAND  OF 
MAN. 
A,  a  serous  tubule;  B,  a  mucous  tubule;  C, 

a  mucous  tubule  with  a  demilune,  d.  Hematein 

and  cosin.     X  665. 


256  MUCOUS  MEMBRANES— GLANDS 

cells  which  compose  the  demilunes.  Many  of  these  cells  contain  an 
independent,,  intracellular,  secretory,  canalicular  system,  which  indi- 
cates a  specific  and  independent  functional  role. 

Mucus,  the  product  of  the  mucus-secreting  cells,  possesses  peculiar 
properties.  In  the  fresh  condition  it  has  a  clear,  glairy  appearance  and 
a  pearly  white  color.  Acted  upon  by  alcohol  or  acids  it  gives  a  heavy 
precipitate  of  stringy  white  flocculi.  Within  the  tissues  these  delicate 
flocculi  stain  slightly,  with  basic  dyes  and  readily  with  the  muchematin 
and  mucicarmin  of  Mayer.  The  very  clear  glairy  appearance  of  the 
fluid  and  the  slightly  basophil  properties  of  the  precipitated  flocculi  are 
so  characteristic  that  when  typical  mucus-containing  cells  are  once  care- 
fully observed  they  can  be  thereafter  readily  distinguished  from  other 
types  of  epithelium. 

Serous-secreting  cells  differ  greatly  in  appearance  with  the  vary- 
ing character  of  their  secretions,  yet  they  present  certain  general  char- 
acteristics. These  cells  are  unquestionably  capable  of  alternate  phases 
of  secretory  activity  and  comparative  rest.  At  the  end  of  a  period  of 
activity  they  appear  shrunken  and  small,  and  the  lumen  of  their  tubule 
is  consequently  increased  in  size.  Their  nucleus  is  centrally  located, 
and  their  cytoplasm  is  relatively  devoid  of  secretion  and  frequently 
presents  a  faintly  rodded  or  striated  appearance. 

During  rest  secretion  accumulates  within  the  cell,  and  the  cytoplasm 
consequently  becomes  either  clearer  or  more  granular,  according  as  the 
nature  of  the  secretion  is  watery,  or  is  granular  and  zymotic  in  char- 
acter; thus  the  secreting  cells  of  the  sweat  glands  become  clearer  as 
their  secretion  accumulates,  whereas  those  of  the  pancreas  become  more 
granular. 

As  a  rule  the  pre-secretion  accumulates  at  the  central  end  of  the  cell, 
the  nucleus  is  thus  crowded  toward  the  basement  membrane  and  is  sur- 
rounded by  the  least  altered  cytoplasm.  The  whole  cell  becomes  swollen 
and  distended  by  the  accumulated  secretion  and  the  tubular  lumen  is 
consequently  diminished  in  size  or  even  occluded. 

Finally  the  period  of  secretory  activity  arrives,  and  the  secretion 
is  poured  into  the  glandular  lumen;  the  cells  become  shrunken  and  the 
lumen  of  the  tubule  correspondingly  dilated.  The  cytoplasm  returns 
to  its  former  condition;  if  the  secretion  is  of  a  granular  character  the 
cell  becomes  clearer,  but  if  watery  the  cytoplasm  acquires  a  finely  granu- 
lar appearance.  The  nucleus  resumes  its  former  central  location  and 
the  cell  enters  upon  a  second  period  of  constructive  and  accumulative 
activity. 


GLANDS  257 

Many  of  the  porous-secret ing  cells  contain  minute  intracellular  canals 
which  connect  with  a  network  of  intercellular  passages  about  the  cell. 
The  intercellular  canaliculi  may,  on  the  one  hand,  open  into  the  glandu- 
lar lumen,  or  they  may  communicate  with  the  tissue  spaces  of  the  tunica 
propria.  This  system  of  intracellular  and  intercellular  canaliculi  may 
thus  serve  either  as  a  system  of  nutrient  channels  or  as  a  network  of 
secretory  capillaries  by  which  the  secretion  is  conveyed  from  the  interior 
of  the  secreting  cells  to  the  lumen  of  the  gland  or  even  to  the  duct 
system.  Nutrient  and  secretory  canaliculi  of  this  nature  have  been 
demonstrated  in  the  secreting  cells  of  the  liver,  cardiac  glands  of  the 
stomach,  salivary  glands,  pancreas,  adrenal,  and  epididymis,  but  they 
are  not  by  any  means  confined  to  the  actively  secreting  cells,  for  they 
have  been  found  in  the  cells  of  bladder  epithelium  (Holmgren)  and 
are  highly  developed  in  the  nerve  cells  (Holmgren,  Golgi,  et  al.). 

DESCRIPTION  OF  HISTOLOGIC  TYPES 

Simple  Tubular  Glands. — Simple  tubular  glands  occur  in  the  mu- 
cous membrane  of  the  small  and  large  intestine  as  the  crypts  of  Lieber- 
kiihn  or  intestinal  glands.  In  shape  these  glands  resemble  a  test-tube. 
They  form  straight  tubules  which  open  on  the  free  surface  of  the  mem- 
brane, are  of  approximately  equal  caliber  throughout,  and  at  their  deeper 
end  terminate  in  a  blind  extremity.  The  tubules  are  lined  with  epi- 
thelium and  are  embedded  in  a  thin  vascular  tunica  propria.  Their 
epithelium  includes  the  usual  columnar  and  goblet  cell  types,  the  latter 
being  more  abundant  near  the  mouth  of  the  gland.  Near  the  blind 
extremity  are  certain  granular  cells,  the  granules  of  some  of  which  are 
slightly  basophilic:  other  cells  possess  coarse  granules  which  are  highly 
acidophil,  as  demonstrated  by  Kultschitsky  (Arch.  f.  mik.  Anat.,  1897) 
in  the  intestinal  glands  of  the  dog,  an  observation  which  is  easily  cor- 
roborated for  the  simple  tubular  glands  in  the  small  intestine  of  man. 

Convoluted  Tubular  Glands.— Convoluted  tubular  glands  occur  as 
the  sweat  glands  of  the  skin,  the  ceruminous  glands  of  the  ear,  and  the 
glands  of  Moll  in  the  eyelids.  The  above  are  typical  simple  coiled 
glands.  Certain  other  glands,  which  are  less  typically  coiled  but  are 
more  or  less  convoluted  near  their  blind  extremities  and  are  frequently 
branched,  are  also  to  be  included  under  this  type.  Such  glands  are  the 
pyloric  glands  of  the  stomach,  and  the  small  mucous  glands  of  the 
oral  and  nasal  cavities,  pharynx,  larynx,  trachea,  bronchi,  and  esophagus. 
Some  of  these  glands,  and  especially  those  of  the  pyloric  end  of  the 
17 


258 


MUCOUS  MEMBRANES— GLANDS 


stomach,,  present  terminal  acinar  dilatations,  hence  they  also  resemble 
to  some  extent  a  small  tubulo-aciiiar  type  of  gland. 

The  typical  coil  glands  consist  of  a  duct  whose  epithelium  resembles 
an  attenuated  layer  of  the  stratified  epithelium  upon  which  they  open, 
and  a  fundus  or  secreting  portion  which  is  lined  by  columnar  epithelium 
of  the  glandular  type.  They  also  possess  a  connective  tissue  basement 
membrane  and  a  vascular  tunica  propria. 

Branched  Tubular  Glands. — Branched  tubular  glands  include  the 
cardiac  and  pyloric  glands  of  the  stomach  and  the  glands  of  the  uterine 
mucous  membrane.  These  glands  possess  a 
duct  whose  epithelium  corresponds  in  type 
with  that  of  the  surface  upon  which  they 
open.  Several  secreting  tubules  open  into 
this  duct  by  means  of  a  short  constricted  por- 
tion, the  neck.  The  fundus  or  secreting 
portion,  after  a  typically  spiral  course,  ends 
with  a  blind  extremity  which  is  often  curved 
or  hooked.  This  portion  of  the  gland  is 
clothed  with  columnar  or  glandular  epi- 
thelium and  invested  with  a  thin  basement 
membrane  and  tunica  propria. 

Compound  Tubular  Glands. — Com- 
pound tubular  glands  include  the  kidney, 
testis,  lacrimal  gland,  and  liver.  The  finer 
structure  of  the  glands  of  this  type  is  so  pe- 
culiar that  the  reader  must  be  referred  to 
the  several  chapters  in  which  they  are  more 
fully  described. 

Compound  Tubulo-alveolar  Glands  (Tubulo-adnar  or  Racemose 
Glands). — This  is  the  most  widely  distributed  of  all  the  types  of  se- 
creting glands.  It  includes  the  parotid,  the  submaxillary,  the  larger 
mucous  and  serous  glands  of  the  oral  cavity,  and  of  the  nose,  pharynx, 
trachea,  brqnchi,  and  esophagus,  the  duodenal  (Brunner's)  glands,  the 
pancreas,  bulbo-urethral  (Cowper's)  glands,  urethral  (Littre's)  glands, 
and  the  large  mucous  glands  of  the  cervix  uteri. 

The  form  of  these  glands  may  be  likened  to  a  much  branched  tree, 
whose  stem  as  the  main  excretory  duct  opens  upon  the  free  surface  of 
a  mucous  membrane,  and  the  branches  and  twigs  as  the  larger  and 
smaller  interlobular  ducts  reach  out  in  all  directions  to  finally  end  in 
minute  alveolar  dilatations,  the  secreting  acini. 


FIG.  257. — MODEL  OP  A  RE- 
CONSTRUCTION OF  THE  LAC- 
RIMAL GLAND  OF  MAN. 

The  tubular  duct  divides 
into  the  terminal  secreting 
tubules,  forming  a  compound 
tubular  gland.  X  170.  (After 
Maziarski.) 


GLANDS 


259 


Except  for  the  ducts  of  certain  mucous  glands  whose  epithelial  coat 
resembles  that  of  the  mucous  membrane  to  which  they  are  attached,  the 
ducts  of  this  type  of  secreting  gland  are 
lined  by  columnar  cells  whose  cytoplasm  fre- 
quently presents  a  rodded  appearance  at  the 
deeper  end  of  the  cell.  The  acini  contain 
typical  serous  or  mucous,  secreting  epithe- 
lium. Occasionally  the  secreting  cells  are 
also  found  for  some  distance  beyond  the 
acinus  in  the  lining  membrane  of  the  small- 
est ducts. 

The  tubules  and  acini  of  these  glands  are 
invested  with  a 
basement  mem- 
brane and  a 
delicate  tunica 
propria.  The 
acini  are  united 
by  the  connec- 
tive tissue  into 
small 


FIG.  258. — RECONSTRUCTION  OP 
A  Mucous  GLAND  FROM  THE 
RESPIRATORY  REGION  OF  THE 
NASAL  MUCOSA  OF  A  CHILD. 

The  duct  passes  directly  into 
secreting  alveoli.    A  typical 
X 


small  tubulo-alveolar  gland, 
which  inclose  a  200.    (After  Maziarski.) 


central  duct  of 

the  smallest  type,  the  intercalary  (or  inter- 
mediate) duct.  These  acinar  groups  are 
again  united  into  the  lobules  of  the  gland 
by  fine  bands  of  connective  tissue,  and 
broader  bands  of  loose  connective  tissue  ce- 
ment the  many  lobules  into  one  glandular 
mass.  .The  intercalary  ducts  by  union  within 
the  lobule  form  numerous  small  intralobular 
ducts  which  approach  the  periphery  of  the 
lobule  and  at  its  margin  open  into  the  inter- 
lobular  ducts;  the  latter  are  found  in  the 
broader  septa  of  connective  tissue  between 
the  lobules.  The  interlobular  ducts  by  union 
with  one  another  result  in  progressively 
larger  branches  which  finally  form  the 
main  excretory  duct  of  the  gland. 

Simple  Saccular  Glands. — Simple    saccular   glands   occur   as   the 


FIG.  259. — RECONSTRUCTION 
OF  AN  INTRALOBULAR  DUCT 
DIVIDING  INTO  ITS  TER- 
MINAL INTERCALARY  DUCTS 
AND  ACINI. 

The  terminal  divisions  of  a 
large  compound  tubulo-aci- 
nar  gland.  The  model  was 
made  from  serial  sections  of 
the  human  pancreas.  X  344. 
(After  Maziarski.) 


260  MUCOUS  MEMBEANES— GLANDS 

smallest  sebaceous  glands  of  the  skin.  These  are  small  glandular  pouches 
with  a  short  duct,  a  constricted  neck,  and  a  dilated  fundus  which,  in- 
stead of  having  a  single  coat  of  epithelium  as  in  most  of  the  tubular 
glands,  is  more  or  less  completely  filled  with  a  mass  of  epithelial  cells. 
The  cells  as  they  approach  the  duct  of  the  gland  show  progressive  stages 
of  degeneration  and  disintegration  which  culminate  in  the  formation 
of  a  thick,  viscid,  fatty  secretion.  Since  these  cells  form  their  secretion 
by  disintegration  they  are  obviously  capable  of  passing  through  the 
various  stages  of  secretory  activity  but  once,  and  hence  they  must  be 
renewed  by  the  repeated  mitotic  cell  division  which  occurs  at  the  periph- 
ery of  the  saccule.  ' 

The  epithelium  of  the  secreting  saccule  rests  upon  a  distinct  base- 
ment membrane  and  is  invested  with  a  very  vascular  tunica  propria. 

Branched  Saccular  Glands— Branched  saccular  glands  include  the 
larger  of  the  sebaceous  glands  of  the  skin,  in  which  several  saccules 
pour  their  secretion  into  a  common  duct,  and  the  tarsal  (Meibomian) 
glands  of  the  eyelids  in  which  a  considerable  number  of  saccules  open 
into  an  axial  canal  by  which  the  secretion  is  conveyed  to  the  terminal 
duct.  The  structure  of  each  glandular  saccule  of  this  type  is  identical 
with  that  of  a  simple  saccular  gland. 

Compound  Saccular  Glands. — This  type  includes  only  the  mam- 
mary gland.  It  consists  of  a  system  of  tubular  ducts  which  possess 
ampullary  dilatations  and  many  branches.  Its  ducts  terminate  in  small 
saccular  alveoli  which  have  a  thin  epithelial  lining.  During  the  period 
of  their  inactivity  the  lining  epithelial  cells  are  much  flattened  and 
the  acini  appear  shrunken.  The  epithelium  of  the  lactating  gland,  011 
the  other  hand,  is  cuboidal  or  columnar,  the  height  being  more  or  less 
dependent  upon  the  accumulation  of  secretion  within  the  cell. 

The  secretion  is  formed  in  the  same  manner  as  in  the  tubular  glands 
with  an  additional  process  of  fatty  infiltration  by  which  fat  droplets 
are  formed  within  the  cytoplasm.  These  droplets  collect  in  the  central 
portion  of  the  cell  and  are  finally  discharged  into  the  lumen  of  the  acinus 
with  apparent  rupture  of  the  cell  membrane  and  the  escape  of  a  portion 
of  its  superficial  cytoplasm.  The  epithelium  is  thus  capable  of  repeated 
secretion. 

The  mammary  glands  may  be  considered  as  offering  an  inter- 
mediate type  between  the  branched  saccular  and  the  tubulo-acinar 
types. 

Ductless  Glands  (Endocrine  Glands}. — Under  the  head  of  glands 
it  is  necessary  to  consider  certain  structures  which  apparently  contain 


GLANDS  2G1 

secreting  epithelium  and  which  present  a  more  or  less  distinct  tubular 
arrangement.  These  bodies  are  the  adrenals,  thyroids,  parathyroids, 
carotid  glands,  coccygeal  gland,  paraganglia,  hypophysis  cerebri,  and 
epiphysis  cerebri  (pineal  gland).  These  are  also  known  as  organs  of 
internal  secretion. 

While  these  glands  do  not  possess  an  excretory  duct,  nevertheless 
some  of  them  certainly,  and  the  others  probably,  form  certain  products 
which  find  their  way  into  the  blood  or  lymph  as  so-called  'internal  se- 
cretions.' The  epithelium  of  the  glands  may  form  either  alveoli,  tubules, 
or  solid  cell  columns,  which  are  supported  by  very  delicate  connective 
tissue  tunics.  Many  blood-vessels,  often  of  the  thin  walled  sinusoidal 
type,  are  found  within  these  tunics  and  are  thus  brought  into  intimate 
relation  with  the  epithelial  parenchyma.  In  some  instances  lymphatics 
are  distributed  in  a  similar  manner  within  the  gland. 

The  property  of  internal  secretion  is  not  peculiar  to  the  ductless 
glands.  It  has  long  been  ascribed  to  the  liver  cells  in  connection  with 
their  influence  upon  nitrogenous  and  carbohydrate  metabolism,  and,  in 
fact,  many  secreting  glands,  even  though  not  of  vital  importance,  are 
nevertheless  found  to  influence  the  economy  in  certain  ways  which  can 
not  be  accounted  for  by  the  properties  of  their  external  secretions. 

Finally,  it  must  be  emphatically  stated  that  the  types  of  secreting 
glands,  as  above  described,  are  not  bound  by  hard  and  fast  lines,  but 
many  forms  will  be  found  which  might  well  be  placed  under  either 
of  two  or  more  types.  Hence  any  classification  of  secreting  glands  be- 
comes more  or  less  arbitrary;  nevertheless  such  a  classification  is  of 
extreme  importance  as  serving  to  establish  in  the  mind  of  the  student 
certain  typical  pictures  with  which  individual  glands  may  be  compared, 
and  important  structural  details  will  thus  be  noticed  which  might  other- 
wise escape  observation. 


CHAPTER    XI 


THE   SKIN 


The  skin,  or  integument,  consists  of  an  outermost  ectodermal  layer 
of  stratified  squamous  epithelium,  the  epidermis  (cuticle),  and  a  sub- 
jacent mesodermal  layer  of  dense  connective  tissue,  the  corium  or  derma 
(derma  vera,  cutis  vera),  homologous  with  the  tunica  propria  of  the 
mucous  membranes.  The  corium  contains  the  nerves  and  the  nerve  end 
organs  of  special  sense,  and  rests  upon  a  subcutaneous  layer  of  areolar 
and  adipose  connective  tissue  which,  blending  with  fascia  or  periosteum, 
unites  the  skin  to  the  underlying  muscles  and  bones. 

The  skin  serves  a  composite  function:  protection,  regulation  of  body 
temperature,  tactile  sensation,  and  excretion.  Its  excretory  role  is  in 
fact  accessory  to  the  kidney. 

The  skin  is  typically  a  stratified  organ,  and  for  convenience  of 
description  may  be  divided  into  the  following  layers : 


SKIN. . 


I.  Epidermis.  - 


"1.  Scaly  layer. 

2.  Flattened  cell  layer. 


Horny  layer; 
stratum  corneum. 


Eleidin-containing  layer ; 
stratum  lucidum 

4.  Granular  laver;  stratuml  _, 

granulosum.  Germinal,  Mal- 

5.  Prickle  cell  layer.  f  plghian  °r  mu' 
~    ^  v   j  •    i      n  i  fious  layer. 

6.  Cylindrical  cell  layer. 

II.  Derma.     JL  PaPm<»7  laycr- 

[2.  Ecticular  layer. 

III.  Subcutaneous  tissue. 


THE  EPIDERMIS 

The  epidermis  (cuticle)  or  scarf  skin  serves  for  the  protection  of 
the  more  sensitive  corium  or  'true  skin/  It  is  formed  by  a  dense  layer 
of  stratified  epithelium  and  varies  in  thickness  in  different  portions 

262 


THE  EPIDERMIS 


263 


of  the  body,  being  thickest  upon  those  surfaces  which  are  exposed  to  the 
greatest  mechanical  violence,  e.g.,  the  palms  of  the  hands  and  soles  of 
the  feet;  and  thinnest  in  the  least  exposed  portions,  e.g.,  inner  sides 
of  the  arms  and  the  back. 

The  layer  of  stratified  squamous  epithelium  composing  the  epidermis 
differs  from  that  of  the  mucous  mem- 
branes in  that  its  superficial  cells  con- 
tain an  abundance  of  keratin,  a  peculiar 
horny  material.  The  production  of 
keratin  in  the  cells  of  stratified  epi- 
thelium appears  to  be  more  or  less  de- 
pendent upon  the  desiccation  which  oc- 
curs in  those  cells  which  form  the  com- 
paratively dry  cutaneous  surface.  The 
cornification  can  scarcely  be  demon- 
strated in  the  stratified  squamous  epi- 
thelium of  the  moistened  mucous  mem- 
brane of  the  mouth,  esophagus,  etc. ;  it 
is  present  though  not  pronounced  in 
the  partially  moistened  margins  of  the 
eyelids,  lips,  labia  minora,  glans  penis, 
etc.  In  the  epidermis,  however,  corni- 
fication is  pronounced  and  characteris- 
tic in  all  portions  of  the  body. 

The  thickness  of  the  cornified  lay- 
ers appears  to  be  in  proportion  to, 
if  not  entirely  dependent  upon,  the 
amount  of  mechanical  violence  to  which 
the  cutaneous  surface  is  subjected.  Ac- 
cordingly the  increased  thickness  of 
the  epidermis  covering  the  palms  and 
soles  is  found  to  be  due  almost  entirely 
to  an  increase  in  the  superficial  horny 
portion  of  the  epidermis,  the  germinal 
layers  being  no  more  pronounced  than  in  other  portions  of  the  body. 

The  epidermal  tissue  is  divisible  into  a  superficial  horny  portion 
consisting  of  flattened,  desiccated,  cornified  cells — the  stratum  corneum 
or  horny  layer — and  a  deeper  protoplasmic,  so-called  'mucous'  portion, 
which  consists  of  polyhedral  and  cylindrical  cells — stratum  germinati* 
vum,  or  mucosum,  rete  mucosum,  rete  Malpighii. 


FIG.  260. — EPIDERMIS  OF  THE  FOOT. 

a,  flattened  cells;  b,  stratum  luci- 
dum;  c,  granular  layer;  d,  germinal 
layer;  e,  cylindrical  cell  layer;  /, 
derma.  Picrocarmin.  Moderately 
magnified.  (After  Ranvier.) 


264 


THE  SKIN 


Cylindrical  Cell  Layer  (Stratum  Cyllmlrlcum). — The  deepest  cells 
of  the  stratum  mucosum  are  elongated  in  a  direction  nearly  perpendicu- 


FIG.  261. — SECTION  OF  THIN  SKIN*  FROM  ABDOMEN  OF  XEGRO,  SHOWING  THE  DISTRI- 
BUTION OF  THE  PIGMENT  GRANULES  IN  DERMAL  AND  EPIDERMAL  CELLS.     X  750. 

lar  to  the  basement  membrane  upon  which  they  rest;  they  are  thus 
irregularly  cylindrical  in  shape.     It  is  these  cells  which  in  the  pig- 

mented  portions  of 
the  body,  i.e.,  areo- 
Ia3  of  the  nipples, 
scrotum,  circu- 
manal  region,  etc., 
and  in  the  skin  of 
brunettes  and  the 
colored  races  con- 
tain the  pigment 
which  gives  rise  to 
the  darkened  color 
of  the  skin. 

In  the  skin  of 

FIG.  262. — SECTION  OF  THIN  SKIN  FROM  ABDOMEN  OF      the  negro,  the  pig- 
LIGHT  BROWN  MULATTO.*  X  750.  ment  (m  e  1  a  11  i  c) 

granules,      while 

most  abundant  in  the  basal  cylindrical  cells,  are  nevertheless  present,  but 
in  progressively  smaller  number,  in  all  of  the  outer  cell  layers.     In  the 


THE  EPIDERMIS  265 

various  shades  of  mulatto  skin,  there  is  a  close  correspondence  between 
the  degree  of  color  and  the  number  of  pigmented  layers  of  epidermal 
cells.  Certain  connective  tissue  cells  of  the  corium  of  pigmented  skins 
also  contain  abundant  melanin  granules;  in  the  darker  skins  such  cells 
are  numerous.  However,  the  dermal  pigmented  cells  are  not  correctly 
regarded  as  the  sources  of  supply  of  melanic  granules  for  the  epidermal 
cells,  as  has  been  maintained.  The  latter  can  produce  their  own 
granules;  both  dermal  and  epidermal  pigmented  cells  owe  their  condi- 
tion to  the  same  underlying  cause  (Jordan;  Amer.  Nat.,  vol.  45,  1911). 
The  pigment  granules  are  said  to  arise  as  a  differentially  staining  nuclear 
substance  ('pyrenoid  substance')  which  passes  through  the  nuclear  mem- 
brane into  the  cytoplasm,  where  it  gradually  acquires  the  character  of 
pigment  granules  (Meirowsky:  "On  the  Origin  of  the  Melanotic  Pig- 
ment in  the  Skin  and  the  Eye,"  Leipzig,  1908).  The  nuclear  origin  of 
the  pre-pigment  granules  is,  however,  disputed  by  some.  The  more  re- 
cent investigations  indicate  that  the  physiology  of  melanic  pigment  for- 
mation involves  the  interaction  of  a  nuclear  oxidase  (tyrosinase)  with 
an  extranuclear,  perhaps  cytoplasmic,  chromogen  (tyrosin). 

The  processes  of  mitotic  cell  division  are  very  active  in  these 
columnar  cells,  and  they,  with  the  adjacent  portion  of  the  prickle  cell 
layer,  form  the  stratum  germinativum  of  Flemming,  in  which  the  re- 
generation of  the  epidermis  occurs.  The  cylindrical  cells  are  firmly 
united  to  the  basement  membrane  by  delicate  cytoplasmic  fibrils,  the 
intercellular  bridges.  Their  nuclei  are  ovoid  in  shape,  and  vesicular  in 
appearance. 

Prickle  Cell  Layer  (Stratum  Spinosum). — Superficial  to  the  cylin- 
drical cells  is  a  stratum  of  polyhedral  epithelium  which  extends  inward 
between  the  adjacent  papillae  of  the  corium  (interpapillary  region  of 
the  epidermis),  and  is  therefore  thick  in  these  portions,  but  is  rela- 
tively much  thinner  over  the  apices  of  the  dermal  papillae  (suprapa- 
pillary  portion  of x the  epidermis). 

The  polyhedral  cells  of  this  layer  contain  a  soft  granular  cytoplasm 
and  a  very  chromatic,  though  vesicular,  spheroidal  nucleus.  They  are 
separated  from  one  another  by  narrow  intercellular  spaces  which  are 
bridged  across  by  innumerable  delicate  cytoplasmic  fibrils.  These  fibrils 
connect  adjacent  cells  and  are  frequently  continued  without  interruption 
through  one,  two,  or  even  three  or  four  neighboring  cells.  Their  course 
is  characteristically  curved,  the  convexity  being  directed  toward  the 
nucleus.  Those  portions  of  the  numerous  cytoplasmic  fibrilla?  which 
span  the  intercellular  spaces  form  the  so-called  intercellular  bridges. 


266 


THE  SKIN 


It  is  because  of  the  resulting  spinous  appearance  that  the  polyhedral 
cells  have  been  termed  prickle  cells  (Schultze). 

In  the  thinner  portions  of  the  epidermis  the  prickle  cells  are  imme- 
diately covered  by  several  layers  of  hard  flattened  cells  whose  nuclei 
have  partially  or  wholly  disappeared,  and  whose  cytoplasm  has  been 
changed  into  a  horny,  keratin-containing  mass.  The  flattening  and 
desiccation  of  these  cells  becomes  more  pronounced  as  they  approach 

the  surface.  In  the 
thin  portions  of  the 
epidermis  the  change 
from  the  prickle  cell 
layer  to  the  horny  lay- 
er is  abrupt. 

In  the  thicker  por- 
tions of  the  epidermis, 
as  in  the  palms  of  the 
hands,  the  change  is 
more  gradual,  and  re- 
sults in  the  appearance 
of  two  additional  cell 
layers,  in  the  cytoplasm 
of  whose  cells  are  in- 
termediate products  of 
chemical  metamorpho- 
sis, keratohyalin  and 
eleidin,  which  may  be 
considered  as  the  prede- 
cessors of  the  keratin 
or  pareleidin  which  is 
peculiar  to  the  cells  of 
the  horny  portion. 

Granular  Layer 
(Stratum  Granulo- 
surn). — In  the  thicker 
parts  of  the  cuticle  the 
most  superficial  prickle 
cells  become  slightly 

flattened,  and  coarse  granules  appear  within  their  cytoplasm.  These 
cells  form  the  granular  layer  (stratum  granulosum),  a  double  cell  layer 
which  occupies  the  superficial  portion  of  the  rete  mucosum. 


FIG.  263. — SKIN  FROM  SOLE  OF  HUMAN  FOOT,  SHOW- 
ING SPIRAL  DUCTS  OF  Two  SWEAT  GLANDS  OPENING 

THROUGH  THE  EPIDERMIS. 

The  stratum  germinativum  is  represented  by  the 
dark,  wavy  line;  below  this  is  the  stratum  papillnre  of 
the  derma,  above  the  stratum  lucidum. 


THE  EPIDERMIS 


267 


The  cells  of  the  granular  layer  are  flattened  and  angular.  They 
possess  an  indistinct,  apparently  degenerating  nucleus,  and  their  cyto- 
plasm contains  large  plate-like  granules  of  Tceratoliyalin  (eleidin  of 
Eanvier),  which  are  strongly  basophil  and  stain  readily  with  most 
nuclear  dyes. 

Eleidin-containing  Layer  (Stratum  Lucidum). — The  granule  cells 
are  abruptly  transformed  into  the  shiny  cells  of  the  stratum  lucidum, 
which  is  the  deepest  layer  of  the  horny  portion  of  the  epidermis.  The 
colls  of  this  layer  possess  an  indistinct  nucleus,  are  irregularly  flattened 
and  angular  in  shape,  are  more  or  less  fused  together  at  their  adjacent 
margins,  and  contain  a  smooth,  highly  refractive,  glassy  cytoplasm  which 
reacts  feebly  to  most  a 

staining   reagents,    but   is 
deeply  colored  by  safranin. 

The  stratum  lucidum 
is  so  named  because  of  its 
highly  refractive  appear- 
ance; it  is  usually  about 
two  cells  thick.  Its  cyto- 
plasm contains  eleidin,  a 
substance  which  is  prob- 
ably intermediate  in  chem- 
ical composition  between 
the  keratohyalin  of  the 
stratum  granulosum  and 
the  keratoid  pareleidin  of 
the  horny  cells. 

Flattened  Cell  Layer 
and  Scaly  Layer  (Stra- 
tum Corneum  and  Stra- 
tum Disjuncium  of  Ran- 
vier). — Above  the  stratum 
lucidum  the  horny  layer 
consists  of  flattened  corni- 
fied  cells  which  are  closely 
packed  and  somewhat  fused  and  blended  with  each  other  at  their  faintly 
serrated  margins.  Intercellular  bridges  and  spaces  have  almost  entirely 
disappeared.  The  nuclei  of  the  cells  are  no  longer  demonstrable,  and 
their  cytoplasm  has  been  changed  into  a  dry,  shiny,  highly  refractive 
mass  of  ' keratin'  (pareleidin)  which  responds  but  slightly  to  ordinary 


FIG.  264. — TRANSECTION  OF  THE  EPIDERMIS  OF  THE 
FOOT. 

a,  superficial  scaly  layer;  b,  layer  of  flattened 
cells,  the  inner  and  outer  portions  of  which  have 
been  characteristically  blackened  by  osmium  tet- 
roxid;  c,  stratum  lucidum;  d,  granular  layer;  e, 
prickle  cells;  /,  cylindrical  cells;  g,  papillary  layer 
of  the  derma.  Osmium  tetroxid,  carmin.  Moder- 
ately magnified.  (After  Ranvier.) 


268  THE  SKIN 

stains.  Its  superficial  layers  stain  deeply  in  osmic  acid,  indicating  a 
considerable  fatty  alteration.  If,  however,  these  cells  are  acted  upon 
by  solutions  of  strong  alkalies,  soda,  potassa,  etc.,  the  outlines  of  the 
degenerated  nuclei  reappear.  As  the  cells  are  pushed  nearer  the  free 
surface,  by  the  process  of  cell  division  in  the  deeper  layers  and  the 
coincident  desquamation  of  cells  from  the  free  surface,  they  become 
more  and  more  flattened  and  desiccated  and  more  completely'  and  firmly 
fused  together  until  at  the  surface  they  form  the  partially  detached 
cell  masses  or  scales — scaly  layer,  stratum  squamosum — which  are 
eventually  removed  by  continued  desquamation. 

It  is  the  thicker  portions  of  the  epidermis  only,  which  possess  all  the 
characteristic  layers  above  described.  In  other  portions  of  the  body 
the  horny  layer  is  much  thinner  (Fig.  262).  In  these  thinner  parts 
the  cuticle  of  the  epidermis  consists  of  a  prominent  rete  mucosum  which 
is  covered  by  a  relatively  very  thin  layer  of  horny  cells.  The  stratum 
granulosum,  in  such  portions,  is  not  usually  demonstrable,  the  stra- 
tum lucidum  is  absent  or  indistinct,  and  the  entire  horny  layer  consists 
only  of  flattened  cornified  cells,  the  more  superficial  of  which  form 
a  very  thin  scaly  layer. 

THE  DERMA 

The  derma  or  corium  (derma  vera,  cutis  vera)  forms  a  connective 
tissue  bed  or  matrix  upon  which  the  epidermis  lies.  It  is  divisible  into 
two  strata,  a  deeper  reticular  layer  in  which  coarse  fiber  bundles  inter- 
lace to  form  a  loose  connective  tissue  network,  and  a  superficial  papil- 
lary layer  in  which  the  finer  bundles  of  connective  tissue  form  a  more 
closely  meshed  network. 

The  Papillary  Layer  (Stratum  Papillare). — The  surface  of  the 
papillary  layer  presents  numerous  conical  elevations,  the  papilla  of 
the  corium,  which  project  into  corresponding  cup-shaped  cavities  in  the 
under  surface  of  the  epidermis.  Many  of  the  connective  tissue  papilla? 
contain  tactile  end-organs  (touch  corpuscles  of  Meissner),  and  terminal 
filaments  of  the  nerve  fibers.  They  may  therefore  be  regarded  as  the 
special  organ  of  tactile  sensation.  Other  papilla?  contain  no  touch  cor- 
puscles but  are  richly  supplied  with  capillary  blood-vessels.  Two  types 
are  thus  distinguished,  the  tactile  papilla  and  the  vascular  papillae. 

Papilla?  are  most  abundant  in  the  palms  of  the  hands  and  the  soles  of 
the  feet,  where  they  are  mostly  arranged  in  rows  which  are  responsible 
for  the  fine  lines  and  ridges  visible  to  the  naked  eye.  In  other  portions 


SUBCUTANEOUS  TISSUE          ,  269 

of  the  body  they  are  less  numerous  and  are  often  less  regularly  disposed. 

The  papillary  layer  consists  entirely  of  white  fibrous  and  elastic  con- 
nective tissues  which  form  a  supporting  membrane  for  the  finer  branches 
of  the  cutaneous  blood-vessels  and  nerves.  The  elastic  tissue  supplies 
a  rich  network  of  fine  fibrils  to  all  portions  of  the  papillary  layer,  and 
just  beneath  the  epidermis  it  forms  a  delicate  elastic  membrane  whose 
fibers  intermingle  with  the  hyaline  cuticular  deposit  of  the  columnar 
epidermal  cells  to  form  a  firm  resistant  basement  membrane.  Many 
of  the  elastic  fibers  of  the  papillae,  especially  the  more  superficial  ones, 
pursue  a  peculiar  archiform  course  from  the  base  to  the  apex  of  the 
conical  papilla?.  In  this  way  they  surround  and  inclose  the  centrally 
situated  capillaries  and  the  tactile  corpuscles  of  the  papilla?. 

The  Reticular  Layer  (Stratum  Reticulare). — The  deeper  portion  of 
the  corium  consists  of  interlacing  bundles  of  connective  tissue  fibers 
which  form  a  dense  meshwork.  These  bundles  are  much  coarser  than 
those  of  the  papillary  layer  with  which  they  are  imperceptibly  blended. 
The  reticular  layer  contains  the  larger  blood-vessels  of  the  corium,  many 
small  nerve  trunks,  the  ducts  and  parts  of  the  secreting  portions  of  the 
sweat  glands,  the  more  superficial  sebaceous  glands,  and  many  of  the 
smaller  hair  follicles.  Lamellar  corpuscles  and  nerve  end-organs  of 
Euffini  are  also  found  in  this  layer. 

The  skin  of  the  face  contains  many  striated  muscle  fibers  which  are 
derived  from  the  insertions  of  the  mimetic  muscles.  The  corium  of  the 
scrotum  (where  it  forms  the  tunica  dartos),  of  the  penis,  perineum, 
and  areola  of  the  nipple  contain  much  smooth  muscle,  intermingled 
with  which  is  a  considerable  amount  of  elastic  tissue. 


SUBCUTANEOUS  TISSUE 

The  subcutaneous  tissue  (tela  subcutanea,  subcutis)  consists  of  bands 
and  septa  of  fibrous  connective  tissue  which  extend  from  the  deeper 
margin  of  the  derma  to  the  underlying  fascia  of  the  muscles,  the  peri- 
osteum of  the  bones,  etc.  The  direction  of  these  fibrous  bundles  is  very 
variable.  The  more  nearly  parallel  to  the  cutaneous  surface  the  fiber 
bundles  are,  and  the  looser  the  meshes  which  they  form,  the  greater  is 
the  mobility  of  the  skin. 

The  meshes  of  the  subcutaneous  network  are  occupied  by  lobules 
of  adipose  tissue.  When  abundant  the  subcutis  is  termed  panniculus 
adiposus.  The  subcutaneous  tissue  contains  the  main  nerve  trunks  and 


270 


THE  SKIN 


larger  blood-vessels  of  the  skin,  the  larger  sudoriparous  and  sebaceous 
glands,  and  the  coarser  hair  follicles.  It  also,  together  with  the  deeper 
part  of  the  derma,  contains  the  nerve  end-organs  of  Pacini,  Kuffini,  and 
the  Golgi-Mazzoni  corpuscles  (see  Chapter  VI). 

Small  bundles  of  smooth  muscle  fibers  which  form  the  arrectores 
pilorum  muscles  take  origin  from  the  deeper  surface  of  the  coriuni  and 
are  inserted  into  that  portion  of  the  hair  follicle  which  is  embedded  in 
the  subcutaneous  tissue.  These  fusiform  or  columnar  muscle  bundles 
are  found  in  connection  with  all  the  hairs,  but  in  the  scalp  they  are 
most  highly  developed  and  lie  most  deeply  in  the  subcutaneous  tissue. 

At  the  level  of  the  vascular 
plexuses  between  the  coriuni 
and  the  tola  subcutanea,  Hiigg- 
quist  (Anat.  Anz.,  45,  2,  1913) 
has  described  a  thick  bundle 
of  smooth  muscle  not  previous- 
ly recognized.  It  lies  directly 
beneath  a  cold  spot,  and  is  not 
found  in  skin  lacking  cold 
spots.  The  muscle  is  believed 
to  contract  rcflexly  when  a  cold 
object  is  placed  on  the  skin  and 
constrict  the  local  blood  supply. 

DEVELOPMENT  AND 
GEOWTH  OF  THE  SKIN 

The  skin  may  be  said  to 
arise  with  the  first  differen- 
tiation of  the  embryo  into 
its  three  germ  layers.  The 
ectoblast,  which  is  at  first  a 
single  cell  layer,  becomes  a 
double  layer  by  the  end  of  the 
first  month.  It  continues  to 
increase  in  thickness  until  by 
the  end  of  the  second  month 
it  can  be  differentiated  into 
two  layers,  a  superficial  periderm  (epitrichium) ,  and  a  deeper  germinal 


FIG.   265. — THREE   EARLY   STAGES   IN   THE 

HlSTOGENESIS   OF   THE   SKIN. 

A,  single-layered  epidermis  from  dorsal 
body  wall  of  a  5  mm.  human  embryo;  B,  two- 
layered  epidermis,  from  dorsal  body  wall  of 
13  mm.  human  embryo;  C,  multiple-layered 
epidermis  from  nose  of  21  mm.  pig  embryo. 
Per,  periderm  (epitrichium) ;  Epi,  epidermis; 
Mes,  mesenchyma  differentiating  into  the 
derma.  X  750. 


CUTANEOUS  APPENDAGES  271 

The  peri  derm  forms  a  layer  of  peculiar  dome-shaped  cells  with  flat- 
tened margins  and  a  vesicular  center.  It  continues  to  form  the  super- 
ficial layer  of  the  epidermis  until  ahout  the  sixth  month,  when  it  is 
lost  by  desquamation.  The  germinal  layer  consists  of  a  deep  stratum  of 
cylindrical  cells  and  one  or  two  superficial  strata  of  spheroidal  vesicular 
cells.  The  latter  are  known  as  the  stratum  intermedium.  By  the  fifth 
or  sixth  month  cell  differentiation  has  advanced  in  the  intermediate 
portion  until  cornification  can  be  distinguished  in  its  superficial  cells. 

Further  development  is  analogous  to  the  growth  of  the  mature  epi- 
dermis; new  cells  are  rapidly  formed  in  the  deeper  portion,  stratum 
germinativum,  and  are  steadily  pushed  toward  the  surface,  their  migra- 
tion being  either  accompanied  by  slight,  or  later  by  more  pronounced 
cornification,  which  in  the  latter  case  gives  rise  to  the  stratum  granulo- 
sum,  stratum  lucidum,  and  horny  layer,  but  in  the  former  produces 
only  relatively  slight  flattening  of  the  superficial  cells  without  the  ap- 
pearance of  keratin  or  the  disappearance  of  the  nucleus. 

The  derma  arises  from  the  superficial  layers  of  the.mesoblast  as 
ordinary  connective  tissue,  in  which  the  appendages  of  the  skin  make 
their  appearance  as  ingrowths  from  the  epidermis.  Certain  mesenchymal 
cells  form  the  smooth  muscle  fibers  of  the  arrectores  pilorum  muscles 
and  of  the  derma  of  those  locations  where  muscle  is  present  in  the  mature 
skin.  Other  mesenchymal  cells  produce  the  fat  lobules  of  the  subcu- 
taneous tissue.  Papilla?  appear  during  the  fourth  or  fifth  month  but 
do  not  attain  their  completed  development  until  much  later. 


CUTANEOUS  APPENDAGES 

The  cutaneous  appendages  include  the  sudoriparous  glands,  the  nails, 
the  hairs,  and  the  sebaceous  glands. 

SUDORIPAROUS  GLANDS 
(Glandules  Sudoriparce,  Sweat  Glands} 

The  sudoriparous  glands  occur  in  all  portions  of  the  skin,  but  more 
abundantly  in  certain  locations,  e.g.,  palms  of  the  hands  and  soles  of 
the  feet, — where  their  number  has  been  estimated  at  between  two  and 
three  thousand  to  the  square  inch — axillae,  groin,  and  circumanal  re- 
gion. Over  the  back,  where  they  are  least  numerous,  their  number  is 
said  to  be  less  than  five  hundred  to  the  square  inch.  They  are  long, 
coiled  or  convoluted,  lulml.ir  glands  whose  secreting  portions  lie  in  the 


272 


THE  SKIN 


subcutaneous  tissue  and  in  the  deeper  part  of  the  corium;  their  ducts 
extend  through  the  corium  to  the  under  surface  of  the  epidermis  where 
the  lining  epithelium  of  the  duct  becomes  continuous  with  the  cells  of 
the  interpapillary  portion  of  the  stratum  germinativum.  In  its  further 
course  through  the  epiderniis  the  duct  of  the  gland  forms  only  a 


Fro.  266. — FROM  A  SECTION  OF  THE  ABDOMINAL  INTEGUMENT  OF  AN  INFANT. 
Beneath  a,  and  a',  sweat  glands  are  seen;  the  secreting  portion  of  a'  is  detached 
from  its  duct;  b,  b,  epidermis;  c,  c,  derma;  d,  d,  panniculus  adiposus.    Hematein  and 
Photo.     X  65. 


tortuous  spiral  cleft  or  passage  whose  wall  is  formed  only  by  the  con- 
centrically placed  cells  of  the  various  epidermal  layers  through  which 
it  passes.  The  glands  of  the  axilla  and  circumanal  region  are  branched. 
The  secreting  or  coiled  portion  of  the  gland  (fundus)  consists  of  a 
secretory  epithelium  resting  upon  a  delicate  hyaline  membrana  propria 
in  whose  outer  portion  afe  concentrically  disposed  connective  tissue 
fibers.  The  inner  portion  of  this  membrane,  contains  many  longitudinal 


CUTANEOUS  APPENDAGES 


273 


fusiform  fibers  whose  nature  is  somewhat  doubtful,  though  they  have 
been  most  frequently  considered  to  be  smooth  muscle  fibers.  These 
fibers  are  frequently  branched,  their  processes  often  extending  between 
the  cells  of  the  secreting  epithelium  nearly  to  the  lumen  of  the  gland. 
The  secreting  epithelium  of  the  fundus  consists  of  tall  columnar 
cells  which  possess  a  large  spheroidal  chromatic  nucleus  and  a  finely 
granular  cytoplasm.  The  basal  portion  of  their  cytoplasm  is  often 
slightly  rodded  and  the  cells  are  so  closely  pressed  together  that  it  is 
frequently  impossible  to  distinguish  their  outlines.  The  secreting  cells 
are  disposed  in  a  single  layer  and,  except  after  active  secretion,  are  so 


ftfrjS'-Jt-Tyf~^  OBS*         -  •    Vigg^ 

®V'».    '<*      (®.®.S, 

'  v W  --^' 

IISj^^^:. --.,... 


: 


-*»^-^^<ijfc:x 


FIG.  267. — SEVERAL  COILS  OF  A  SUDORIPAROUS  GLAND  OF  THE  HUMAN  FINGER. 

a.  secreting  portions,  their  lumen  containing  traces  of  secretion;  b,  ducts;  TO,  muscle 

cells.     Hematein  and  picrofuchsin.     X  550. 

tall  as  to  leave  only  a  very  narrow,  central,  glandular  lumen.  During 
secretory  activity  the  cells  become  shrunken  and  their  cytoplasm  more 
granular.  After  a  period  of  rest  the  cytoplasm  again  becomes  clear 
and  vesicular  in  appearance  and  the  cells  are  much  distended.  The 
secretion  reaches  the  lumen  through  intra-  and  intercellular  canaliculi. 
The  ducts  are  lined  by  a  double,  occasionally  triple,  layer  of  some- 
what flattened  epithelial  cells,  which  rest  upon  a  delicate  membrana 
propria  continuous  with  that  of  the  secreting  portion.  The  gross  di- 
ameter of  the  duct  is  much  less  than  that  of  the  secreting  portion  of 
the  gland,  yet  the  lumen  of  the  duct  may  be  larger.  That  portion 
of  the  duct  which  is  lined  by  the  thin  stratified  epithelial  layer  pursues 
a  spiral  course  through  the  subcutaneous  tissue  and  the  derma.  It  finally 

J8 


274  THE  SKIN 

reaches  the  epidermis,  which  it  enters  in  the  interval  between  the  dermal 
papillae  (iuterpapillary  portion  of  the  epidermis).  Its  lining  epithelium 
is  continuous  with  that  of  the  stratum  germinativum,  and  in  its  course 
through  the  epidermis  the  wall  of  the  duct  consists  solely  of  the  sur- 
rounding epidermal  cells.  The  stratum  granulosum  and  adjacent  portion 
of  the  horny  layer  in  the  immediate  neighborhood  of  the  duct  is  in- 
vaginated  into  the  stratum  mucosum,  which  is  thus  considerably  thinned 
by  the  passage  of  the  duct. 

The  sweat  glands  are  abundantly  supplied  with  capillary  blood- 
vessels and  small  non-medullated  nerves,  which  form  plexuses  about 
the  walls  of  the  coiled  portion  of  the  gland,  and  from  which  terminal 
fibrils  penetrate  the  basement  membrane  and  end  in  contact  with  the 
secreting  cells. 

Development. — The  sudoriparous  glands  first  appear  in  the  embryo 
during  the  fifth  month  as  solid  columnar  ingrowths  from  the  stratum 
germinativum  of  the  epidermis.  These  processes  grow  inward  through 
the  primitive  corium  to  its  junction  with  the  looser  subcutaneous  tissue. 
Here  the  cell  columns  become  thickened  and  convoluted,  and  at  about 
the  same  period  their  lumen  appears.  The  glandular  lumen  is  not  at 
first  connected  with  the  free  surface,  but  as  the  cells  of  the  germinal 
layers  of  the  epidermis  gradually  replace  those  which  are  more  super- 
ficial the  epidermal  portion  of  the  duct  is  formed.  At  about  the  seventh 
month  the  lumen  of  the  duct  opens  upon  the  epidermal  surface. 

The  membrana  propria  of  the  fundus  and  dermal  portion  of  the 
duct  is  derived  from  the  surrounding  connective  tissue  elements  of  the 
mesenchyma. 

THE  NAILS 

The  nails  are  produced  by  a  peculiar  modification  of  the  epidermis 
by  which  the  stratum  lucidum  becomes  greatly  thickened  (Bowen,  1899) 
while  the  horny  layer  (eponychium  of  the  embryonic  nail)  is  at  the  same 
time  wanting.  The  nail  is  divisible  into  the  nail  body  and  nail  root; 
the  former  comprising  the  exposed,  the  latter  the  hidden  portion  of 
the  organ.  The  root  of  the  nail  is  overhung  by  a  fold  of  the  skin,  the 
thickened  horny  layer  at  the  margin  of  which  forms  an  adherent  border, 
the  eponychium  of  the  adult  nail. 

The  nail  groove  or  sulcus  is  included  between  the  overhanging  skin 
and  the  root  of  the  nail.  It  is  deep  at  its  proximal  end  but  is  shallow 
at  the  lateral  margins  of  the  nail.  The  distal  or  free  border  of  the  nail 
projects  over  the  skin  at  the  tip  of  the  finger  and  the  thickening  of 


CUTANEOUS  APPENDAGES  275 

the  horny  layer  of  the  subjacent  epidermis  forms  the  so-called  hypony- 
cltiuin. 

Finer  Structure. — The  nail  consists  of  two  layers,  the  superficial 
stratum  lucidum  and  the  deeper  germinal  layer.  These  are  continuous 
at  the  border  of  the  nail  with  the  corresponding  layers  of  the  epidermis 
which  lines  the  nail  groove.  At  the  distal  border,  however,  the  nail 

FEN  H 


268. — TERMINAL  PHALANX  OF  FINGER  OF  HUMAN  FETUS. 

Showing  N,  nail;   F,  nail  fold;  H,  hyponychium;  E,  eponychium;  developing 
sudoriparous  glands,  and  developing  bone. 

proper  or  thickened  stratum  lucidum  ends  in  a  free  margin.  The  finer 
structure  of  these  two  layers  does  not  essentially  differ  from  that  of 
the  corresponding  layers  of  the  epidermis. 

The  stratum  lucidum  in  the  body  of  the  nail  is  very  thick  and  its 
cells  are  so  completely  blended  with  each  other  through  the  excessive 
eleidin  production  that  it  is  impossible  to  distinguish  their  outlines. 
By  maceration  in  alkaline  solutions,  however,  the  outlines  of  both  cells 
and  nuclei  may  be  caused  to  reappear.  In  the  nail  root  the  stratum 
lucidum  increases  rapidly  in  thickness  as  it  grows  distalward;  in  the 
body  of  the  nail  this  layer  is  not  very  materially  thickened  as  it  ap- 
proaches the  distal  or  free  margin. 

The  stratum  germinativum  is  of  nearly  equal  thickness  in  all  por- 
tions of  the  nail  body.  In  the  nail  root  it  is  somewhat  thicker  and 


276 


THE  SKIN 


forms  the  nail  matrix  of  Kanvier.  In  this  portion  also  is  a  distinct 
stratum  granulosum,  a  layer  which  is  absent  or  rudimentary  beneath 
the  body  of  the  nail.  It  is  the  presence  within  this  layer  of  numerous 
keratohyalin  granules  which  renders  the  root  of  the  nail  opaque  and 
thus  forms  the  dull  white  lunula  which  contrasts  with  the  transparent, 

eleidin-containing,  stratum 
lucidum,  which  latter  layer 
alone  covers  the  germinal 
layer  of  the  nail  body  (Unna). 
The  NaH  Bed.— The  nail 
rests  upon  a  very  vascular  ce- 
rium or  nail  bed  (matrix  of 
authors)  which  is  continuous 
with  the  corium  or  derma  of 
the  skin.  The  nail  bed  is  some- 
times regarded  as  active  in  nail 
formation,  but  this  process  is 
now  generally  believed  to  be 
limited  to  the  matrix  of  the 
root.  The  nail  bed  at  the 
margins  of  the  nail  is  provided 
with  papillae  as  in  other  por- 
tions of  the  skin,  but  beneath 
the  body  of  the  nail  its  surface 
is  raised  into  longitudinal 
ridges  which  possess  only  very 
minute  secondary  papillae. 

Nail  Growth.— The  growth 
of  the  nail  occurs  in  the  matrix 
of  the  nail  root.  The  cells  of 

the  stratum  germinativum  of  this  portion,  having  been  once  formed  by 
active  mitosis  push  obliquely  forward  and  outward  toward  the  nail  body. 
It  is  thus  that  the  more  advanced  are  constantly  carried  onward  toward 
the  free  border.  The  growth  of  the  nail  occurs  at  the  rate  of  about  one 
thirty-second  of  an  inch  per  week  (Schafer). 

Development. — In  the  fetus  the  nail  appears  as  a  direct  formation 
of  the  epidermis,  which  is  very  early  evidenced  by  a  thickening  of 
the  stratum  lucidum  in  the  nail  area.  The  nail  is  therefore  at  first 
covered  by  the  superficial  peridermal  cells  of  the  cuticle.  The  nail  groove 
is  rapidly  formed  by  an  invasion  of  the  mesoblast  by  the  epidermal 


FIG.  269. — TBANSECTION  THROUGH  THE  MAR- 
GIN OF  A  FINGER  NAIL. 

On  the  left  is  the  skin,  on  the  right  the  nail, 
a,  a',  horny  layer;  6,  6',  germinal  layer;  c,  c', 
corium;  d,  margin  of  the  nail;  s,  nail  sulcus. 
Moderately  magnified.  (After  von  Brunn.) 


THE  HAIR 


277 


cells  which  become  piled  up  at  the  margin  of 
the  groove  to  form  an  excessive  horny  layer, 
the  definitive  representative  of  the  embryonic 
eponychium.  At  the  distal  extremity  of  the 
nail  the  superficial  cells  are  also  accumulated 
into  a  considerable  mass  which  forms  a  promi- 
nent hyponychium.  Further  growth  of  the  nail 
pushes  its  distal  margin  forward  over  the 
hyponychium  so  that  the  border  becomes  free 
shortly  prior  to  birth.  The  peridermal  cells  are 
then  shed  and  the  nail  body  finally  presents,  at 
about  the  time  of  birth,  its  naked  stratum  lu- 
cidum. 


THE  HAIR 

Development. — The  structure  of  the  hair 
will  be  most  readily  appreciated  if  preceded  by 
a  brief  introductory  sketch  of  its  development. 

THE  HAIR  GERM. — The  hairs  arise  at  any 
time  after  the  third  month  of  fetal  life,  their 
earliest  anlage  appearing  as  a  slightly  increased 
proliferation  of  the  cells  of  the  germinal  layer 
of  the  epidermis.  The  further  multiplication 
of  the  cylindrical  cells  produces  a  solid  colum- 
nar ingrowth  of  the  epidermis  which  pene- 
trates into,  and  sometimes  through,  the  primi- 
tive derma.  The  spheroidal  cells  of  the  inter- 
mediate layer  of  the  epidermis  increase  in  size, 
assume  a  vesicular  character,  and  finally  by 
fatty  degeneration  form  the  epidermal  hair 
canal  through  which  the  future  hair  reaches  the 
surface. 

THE  HAIR  COLUMN. — The  columnar  epi- 
dermal ingrowths,  hair  columns  or  hair  pegs, 
come  into  early  relation  with  the  anlage  of  the 
hair  papilla  which  is  formed  by  a  proliferation 
of  the  mesenchymal  cells  at  the  tip  of  the  hair 
column.  Further  development  of  the  papilla 


FIG.  270. — LONGITUDINAL 
VERTICAL  SECTION  OF 
THE  YOUNG  NAIL  AND 
NAIL-BED  OP  AN  IN- 
FANT. 

n.  r.,  nail  root  or  lunula; 
n.,  nail;  n.  b.,  nail  bed; 
e.,  eponychium;  h.,  hy- 
ponychium. (From  Dahl- 
gren  and  Kepner.) 


FIG.  271. — FIVE  STAGES  IN  THE  DEVELOPMENT  OP  A  HUMAN  HAIR. 
a,  papilla;  b,  arrector  pili;  c,  the  line  is  directed  toward  the  primordial  shaft; 
d,  cells  which  form  the  hair  canal;  e,  sebaceous  gland;  /,  hair  germ  in  epidermis; 
7,  hail  shaft;  h,  Henle's  layer;  i,  Huxley's  layer;  k,  cuticle  of  the  root  sheath,  ( 
inner  root  sheath;  m,  outer  root  sheath  in  tangential  section;  n,  outer  root  sheath 
in  longitudinal  section;  o,  dermal  root  sheath;  P,  epithelial  bed.  X  460.  (After 
Stohr.) 

278 


THE  HAIR  279 

produces  an  indentation  of  the  advancing  hair  column  and  gives  rise  to 
a  true  dermal  papilla  of  considerable  size. 

THE  HAIR  BULB. — Coincident  with  the  formation  of  the  papilla 
there  is  an  increased  proliferation  of  the  cells  of  the  hair  column  by 
which  it  is  surrounded,  and  which  therefore  represents  the  future  hair 
bulb.  Two  other  swellings  appear  in  the  hair  column;  one,  the  more 
superficial,  forming  the  anlage  of  the  sebaceous  gland,  and  the  other, 
the  deeper,  forming  the  so-called  epithelial  bed  or  matrix  of  the  hair 
which  stands  in  close  relation  with  the  growth  and  future  regeneration 
of  the  hair.  This  second  swelling  is  sometimes  interpreted  as  simply 
offering  a  point  of  attachment  for  the  arrector  pili  muscle. 

The  development  of  the  hair  papilla  produces  a  slight  evagination 
of  the  epithelium  of  the  hair  bulb,  which  is  just  sufficient  to  redirect 
the  growth  of  central  cells  of  the  hair  column  toward  the  cutaneous 
surface.  It  is  thus  that  the  younger  cells  which  arise  by  mitosis  in 
the  germinal  layers  of  the  hair  bulb  are  pushed  outward  along  the  axis 
of  the  hair  column  where  they  form  the  shaft  of  the  future  hair.  The 
growth  of  the  hair  from  the  germinal  cells  of  the  hair  bulb  is  accom- 
panied by  beginning  cornification  of  the  newly  formed  cells  of  the  primi- 
tive hair  shaft  and  of  the  intermediate  cells  of  the  hair  column.  The 
growth  of  the  shaft  is,  however,  preceded  by  enlargement,  vesiculation, 
and  fatty  degeneration  of  the  central  cells  of  the  hair  column,  thus 
producing  a  central  canal  through  which  the  hair  may  grow,  and  which 
later  becomes  continuous  with  the  hair  canal  of  the  epidermis. 

THE  HAIR  FOLLICLE. — At  this  stage  the  hair  column  has  become 
differentiated  into  a  peripheral  follicle,  the  primitive  root  sheath,  and 
a  central  hair.  Continued  multiplication  of  the  cells  in  the  germinal 
layer  of  the  bulb  pushes  the  advancing  tip  of  the  hair  nearer  and  nearer 
the  surface  until  it  forces  its  way  into  the  epidermal  hair  canal.  Finally 
the  thin  cuticular  covering  is  ruptured  and  the  eruption  of  the  hair 
shaft  occurs. 

Further  differentiation  of  the  cells  of  the  epidermal  root  sheath  and 
the  formation  of  a  mesenchymal  or  dermal  sheath  of  connective  tissue 
completes  the  development  of  the  hair  follicle.  This  process  is  fre- 
quently repeated  and  results  in  the  formation  of  new  hairs  not  only 
during  fetal  life,  but  also,  in  constantly  decreasing  numbers,  through- 
out childhood  and  adult  life. 

The  Mature  Hair. — Its  development  teaches  that  the  hair  follicle, 
being  formed  as  it  were  by  an  invagination  of  the  epidermis,  contains 
a  dermal  and  an  epidermal  sheath  and  that  the  outer  portion  of  the 


280 


THE  SKIN 


latter,  being  identical  with  the  deeper  portion  of  the  epidermis,  must 
possess  a  close  structural  resemblance  to  the  rete  mucosum,  while  its 
inner  portion,  like  the  horny  layer  of  the  skin,  is  more  or  less  cornified. 
There  is  thus  an  outer  and  an  inner  epidermal  root  sheath  corre- 


FIG.  272. — FROM  A  SECTION  OF  THE  SKIN  OF  AN  INFANT'S  ARM,  SHOWING  SMALL 
IMMATURE  HAIR  FOLLICLES  IN  TR/.NSECTION. 

a-a,  epidermis;  b-b,  derma;  c-c,  subcutaneous  connective  tissue;  d-d,  muscle. 
Hematein  and  eosin.     Photo.     X  95. 

spending  respectively  to  the  mucous  and  horny  layers  of  the  epidermis; 
the  cornified  portion,  inner  root  sheath,  becomes  progressively  thinner 
toward  the  hair  bulb.  The  hair,  on  the  other  hand,  represents  an  ex- 
cessively developed  horny  layer  whose  rete  mucosum  is  found  in  the 
germinal  layer  of  the  hair  bulb. 

The  mature  ha,ir  is  divisible  into  a  hair  shaft  or  free  portion,  and  a 
hair  root  or  concealed  portion.     The  latter  is  inclosed  within  an  epi- 


THE  HAIR  281 

dermal  and  a  dermal  root  sheath  which  together  form  the  hair  follicle. 

THE  HA  in  SHAFT. — Sections  of  the  hair  shaft  present  a  thin  cuticle 
which  consists  of  delicate  horny  scales  whose  free  edges  are  imbricated 
upward,  viz.,  toward  the  tip  of  the  hair.  Within  the  cuticle  the  hair 
may  consist  solely  of  a  hair  cortex  formed  by  flattened  and  very  much 
elongated  horny  epithelial  cells,  which  frequently  retain  the  remnant 
of  a  nucleus,  and  whose  keratized  cytoplasm  is  often  much  pigmented; 
or  the  axis  of  the  coarser  hair  may  contain  enlarged  angular  cells  in 
which  eleidin  granules  and  much  pigment  are  found.  In  the  latter  case 
the  hair  is  said  to  possess  a  medulla.  The  medulla  is  seldom  if  ever 
present  throughout  the  entire  length  of  the  hair.  When  present  it 
sometimes  contains  numerous  air  bubbles  which,  together  with  the 
paucity  of  pigment,  produce  the  lighter  shades  of  hair  peculiar  to  certain 
individuals. 

In  the  light  of  its  development  it  is  obvious  that  the  several  layers 
of  the  hair  shaft  are  comparable  to  the  homologous  layers  of  the  horny 
epidermis,  the  cuticle,  cortex,  and  medulla  of  the  hair  being  respectively 
homologous  with  the  scaly  layer,  the  flattened  cell  layer,  and  the  eleidin- 
containing  layer  or  stratum  lucidum  of  the  epidermis. 

THE  HAIR  ROOT. — The  root  of  the  hair,  except  for  the  fact  that  it 
is  immediately  invested  with  a  hair  follicle,  does  not  in  any  way  differ 
in  structure  from  the  hair  shaft.  It  possesses  the  same  three  layers,  the 
medulla,  however,  being  very  irregularly  developed. 

The  imbricated  cells  of  its  cuticle  interdigitate  with  the  similar 
cells  of  the  cuticle  of  the  inner  root  sheath  in  the  deeper  half  of  the 
follicle;  in  its  superficial  half,  viz.,  above  the  opening  of  the  sebaceous 
gland,  a  narrow  space  intervenes  between  the  cuticle  of  the  hair  and  that 
of  the  root  sheath. 

The  axis  of  the  hair  root  is  always  inclined  at  an  angle  to  the  epi- 
dermis; it  therefore  makes  with  the  epidermis  an  obtuse  angle  on  one 
side  and  an  acute  angle  on  the  other.  The  arrector  pili  muscle  is  always 
found  on  the  side  of  the  obtuse  angle;  it  therefore,  by  drawing  the  hair 
follicle  and  its  inclosed  hair  root  nearer  the  perpendicular,  causes  the 
erection  of  the  hair.  The  sebaceous  gland  is  included  in  the  angle  be- 
i  \\ccti  the  arrector  muscle  and  the  hair  follicle.  Contraction  of  the 
muscle  may  aid  also  in  the  expulsion  of  the  sebum.  Extreme  contraction 
of  the  arrectores  pilorum  muscles  may  result  from  fright,  causing  the 
hair  to  'stand  on  end';  in  a  similar  manner  cold  air  may  effect,  through 
the  pilomotor  fibers,  the  erector  muscles  of  the  small  hairs  distributed 
over  the  body  and  cause  the  so-called  'goose-flesh.' 


FIG.  273. — FROM  A  SECTION  OF  THE  HUMAN  SCALP. 

Ap,  arrector  pili  muscle;  c,  corium;  ep,  epidermis;  fp,  epidermal  root  sheath; 
Gap,  muscular  aponeurosis;  gls,  sudoriparous  gland;  glse,  sebaceous  gland;  KH, 
so-called  'club-hairs'  in  various  stages  of  molting  and  regeneration;  pp,  papilla  of 
the  hair;  Re,  fibrous  band  in  the  subcutaneous  tissue;  Rp,  hair  root;  Sp,  hair  shaft; 
Is,  subcutaneous  adipose  tissue.  Hematoxylin  and  eosin.  X  15.  (After  Sobotta.) 

282 


THE  HAIR  283 

THE  EPIDERMAL  ROOT  SHEATH. — The  epidermal  root  sheath  con- 
sists of  an  inner  and  an  outer  portion,  each  of  which  at  about  the  mid- 
level  is  divisible  into  three  layers  corresponding  to  the  three  similar 
layers  of  the  horny  and  the  mucous  portions  of  the  epidermis.  In  those 
portions  of  the  follicle  and  in  those  individual  hairs  in  which  the  process 
of  cornification  is  less  advanced  these  subdivisions  cannot  all  be  demon- 
strated, and  it  is  only  in  the  most  highly  developed  hairs  that  they 
are  typically  found.  This  is  in  accordance  with  the  structure  of  the 
epidermis,  in  which  the  subdivisions  of  its  horny  and  mucous  portions 
are  typically  found  only  in  the  more  highly  developed  portions,  e.g.,  the 
palms  and  soles. 

Inner  Root  Sheath. — The  cuticle  of  the  inner  root  sheath  consists  of 
thin  horny  epithelial  scales  which  are  imbricated  downward,  viz.,  toward 
the  hair  bulb,  and  which  interdigitate,  in  the  deeper  portion  of  the  fol- 
licle, with  the  similar  scales  of  the  hair  cuticle.  The  direction  of  the 
imbrication  explains  the  removal  of  the  epidermal  root  sheath  when  the 
hair  is  artificially  extracted. 

The  mid-layer  of  the  inner  root  sheath,  layer  of  Huxley,  one  or  two 
cells  thick,  consists  of  horny  cells  which  are  somewhat  flattened,  and  in 
which  the  semblance  of  a  nucleus  is  sometimes  present.  It  corresponds 
to  the  flattened  cell  layer  of  the  epidermis. 

The  outer  layer  of  the  inner  root  sheath,  layer  of  Henle,  is  frequently 
wanting  or  imperceptibly  blended  with  the  preceding  layer.  Its  cells 
are  clear  and  highly  refractive  and  their  nuclei  can  but  rarely  be  demon- 
strated in  the  usual  microscopical  preparations.  The  layer  is  seldom 
more  than  one  cell  deep.  "It  is  homologous  with  the  stratum  lucidum  of 
the  epidermis. 

Outer  Root  Sheath. — The  outer  root  sheath  is  continuous  with  the 
stratum  mucosum  of  the  epidermis  and  therefore  contains  similar  cell 
types.  The  granular  layer,  as  in  the  epidermis,  is  frequently  absent  or 
rudimentary,  but  can  be  readily  demonstrated  in  hematein-stained  sec- 
tions of  the  more  highly  developed  hair  follicles.  It  rests  upon  a  layer, 
several  cells  deep,  of  spheroidal  prickle  cells.  The  outermost  layer  of 
the  outer  root  sheath  is  formed  by  a  basal  layer  of  cylindrical  cells. 
It  grows  progressively  thinner  toward  the  hair  bulb,  where  its  cells 
become  mingled  with  the  germinal  cells  of  the  hair  matrix. 

DERMAL  EOOT  SHEATH. — The  dermal  root  sheath  presents  three 
layers,  an  innermost  basement  membrane  or  glassy  layer,  a  layer  of 
circular  connective  tissue  fibers  and  a  similar  layer  of  longitudinal 
fibers.  These  layers  are  obviously  homologous  with  the  basement  mem- 


284 


THE  SKIN 


brane,  the  papillary  layer,  and  the  reticular  layer  of  the  derma,  respec- 
tively.    The  dermal  root  sheath  is,  however,  devoid  of  papilla?. 


a  b 


FIG.  274. — TRANSECTION  OF  A  HAIR  NEAR  THE  MIDDLE  OF  THE  ROOT  SHEATH. 

a,  dermal  root  sheath;  b,  outer  margin  of  the  epidermal  root  sheath — the  light 
space  is  the  glassy  membrane,  the  polyhedral  cells  form  the  outer  root  sheath;  c, 
Henle's  layer  of  the  inner  root  sheath;  d,  Huxley's  layer;  e,  cuticle  of  the  root  sheath; 
/,  cuticle  of  the  hair;  g,  cortex  of  the  hair  shaft.  Highly  magnified.  (After  Kolliker.) 


The  glassy  membrane  is  a  peculiarly  thick  homogeneous  membrane 
which  is  chiefly  mesoblastic  in  origin,  but  whose  innermost  portion  is 
formed  as  an  exoplasmic  product  of  the  adjacent  epithelium.  This 


THE  HAIR  285 

membrane  is  highly  refractive  and  contains  very  few  connective  tissue 
cells  or  fibers. 

The  circular  fibers  of  the  dermal  root  sheath  contain  interlacing 
bundles  of  connective  tissue  fibers,  which  are  mostly  disposed  in  a  ring- 
like  manner.  Elastic  fibers  are  absent.  Within  this  layer  is  a  dense 
anastomosing  plexus  of  capillary  blood-vessels,  together  with  a  rich 
subepithelial  plexus  of  non-medullated  nerve  fibers. 

The  longitudinal  fibers  of  the  connective  tissue  root  sheath  also  form 
interlacing  fiber  bundles,  most  of  which  are  somewhat  obliquely  disposed. 
The  bundles  are  coarser  than  those  of  the  preceding  layer  and  contain 
a  few  elastic  fibers.  This  portion  of  the  root  sheath  contains  many  small 
blood-vessels  and  nerves  which  supply  the  plexuses  of  the  circular  layer. 

The  hair  follicle  in  transverse  section  varies  in  different  races  from 
circular  to  elliptical  form.  In  the  Chinese  race  the  diameter  of  the  fol- 
licle and  the  hair  is  100  X  77  to  85,  in  the  European  100  X  G2  to  72, 
and  in  the  Negro  100  X  -±0  to  60.  The  more  elliptical  the  form  of  the 
follicle  the  greater  the  curl  of  the  hair. 

ATYPICAL  PORTIONS  OF  THE  HAIR  FOLLICLE. — As  already  indicated, 
the  hair  follicle  presents  some  structural  differences  at  various  levels. 
The  typical  arrangement  is  found  only  in  the  mid-portion  of  the  fol- 
licle. 

In  its  superficial  portion  the  hair  lies  free  in  the  follicular  lumen, 
the  interval  between  it  and  the  inner  root  sheath  being  only  partially 
occupied  by  the  fatty  secretion  of  the  sebaceous  gland  which  enters  the 
lumen  of  the  follicle  at  the  deeper  portion  of  its  middle  segment.  At 
this  level  also,  the  root  sheaths  of  the  hair  offer  a  gradual  transition 
from  their  typical  structure  to  that  of  the  dermal  and  epidermal  layers 
with  which  they  are  continuous. 

The  hair  bulb  .likewise  differs  prominently  from  the  typical  struc- 
ture of  the  hair  root.  In  this  portion  the  germinal  layers  are  very 
highly  developed  at  the  expense  of  the  horny  layers.  It  is,  therefore, 
in  this  portion  that  growth  is  most  active.  The  cells  of  this  region  are 
often  deeply  pigmented.  The  increased  size  of  the  germinal  layer,  more- 
over, produces  a  distinct  bulging  of  the  follicle,  which  incloses  the  hair 
papilla  and  results  in  the  peculiar  bulbous  shape  of  the  extremity  of  the 
hair  follicle. 

THE  HAIR  PAPILLA. — The  structure  of  the  hair  papilla  is  identical 
with  that  of  the  vascular  papilla?  of  the  derma  except  that  it  is  con- 
structed upon  a  much  larger  scale.  It  consists  of  a  conical  or  club- 
shaped  elevation  of  connective  tissue  which  indents  the  extremity  of 


286  THE  SKIN 

the  hair  bulb.  It  contains  an  abundant  plexus  of  capillary  blood-vessels 
and  a  rich  supply  of  non-medullated  nerves.  It  also  contains  an  undue 
proportion  of  connective  tissue  cells. 

REGENERATION  OF  THE  HAIR. — Hairs  are  being  continuously  shed 
and  regenerated,  the  average  life  of  a  hair  of  the  scalp  being  stated  as 
sixteen  hundred  days  (Stohr).  The  shedding  of  a  hair  is  first  heralded 
by  an  atrophy  of  its  papilla  and  a  cornification  of  its  bulb.  Growth 
ceases,  and  the  hair,  firmly  adherent  to  its  root  sheath,  is  gradually 
carried,  by  the  continued  growth  of  the  latter,  nearer  and  nearer  the 
surface  of  the  skin. 

Its  excursion  leaves  behind  a  narrowed  cell  column  which  still  unites 
the  hair  with  its  former  papilla. 

From  this  rudiment  a  new  hair  germ  may  form  (Unna),  a  new  papilla 
develop,  and  the  resulting  hair  grow  toward  the  surface  in  the  path  of 
the  molting  hair,  its  eruption  being  preceded  by  the  falling  of  its  pred- 
ecessor. The  formation  of  the  new  hair  germ  very  probably  occurs  at  a 
point  nearly  corresponding  with  the  insertion  of  the  arrector  pili  muscle, 
where  there  is  a  swelling  of  the  root  sheath  which  has  been  already  men- 
tioned as  the  matrix  of  the  hair  follicle.  This  matrix  appears  very 
early  in  the  development  of  the  hair,  but  remains  quiescent  until  regen- 
eration becomes  necessary,  when  the  cells  are  said  to  proliferate  and 
grow  downward  filling  the  space  between  the  atrophic  hair  and  the  new 
bulb. 

In  infancy  and  youth  shed  hairs  are  also  compensated  for  by  new 
formation  from  hair  germs  appearing  at  the  germinal  border  of  the  epi- 
dermis, the  process  proceeding  in  the  manner  already  described  for  the 
development  of  the  hair. 

THE  SEBACEOUS  GLANDS 

These  are  branched  saccular  glands  which  may  be  subdivided  into 
two  classes,  (1)  those  whose  ducts  open  into  the  hair  follicles,  and  (2) 
those  whose  ducts  open  upon  the  free  surface  of  the  epidermis.  The 
former  are  by  far  the  more  numerous;  the  latter  occur  in  the  skin  of 
the  face,  red  margins  of  the  lips,  labia  minora,  glans  penis  and  prepuce, 
and  the  tarsal  glands  of  the  eyelids.  With  the  above  exceptions  the  dis- 
tribution of  the  sebaceous  glands  is  coextensive  with  that  of  the  hairs. 
They  are  therefore  absent  from  the  palms  of  the  hands  and  soles  of 
the  feet. 

A  sebaceous  gland  consists  of  a  dilated  saccular  fundus,  a  constricted 


FIG.  275. — REGENERATION  OF  A  HAIR. 

Only  the  follicles  and  the  inclosed  portion  of  the  hair  shafts  are  represented.    The 

various  stages  are  numbered  in  order.     (After  Unna.) 

287 


288 


THE  SKIN 


neck,  and  a  short  and  narrow  duct.  Occasional  glands  are  formed  by  a 
single  saccule,  but  more  frequently  they  are  compound,  the  several  sac- 
cules  opening  by  a  single  short  duct  which  is  lined  by  flattened  cells. 
In  the  tarsal  glands  the  secreting  saccules  are  connected  with  the  long 


a 


FIG.  276. — SEBACEOUS  GLANDS  IN  THE  SCALP  OF  A  CHILD. 

a,  hair  follicle;  b,  sebaceous  gland;  c,  hair  follicles  in  oblique  section;  d,  horny 
layer  of  the  epidermis;  e,  germinal  layer;  /,  derma;  g,  blood-vessel.    Hematein  and 
Photo.     X  83. 


excretory  duct  by  means  of  a  short  intercalary  duct.  The  fatty  secretion 
of  the  sebaceous  glands,  sebum,  is  formed  by  the  direct  disintegration 
of  the  protoplasm  of  the  glandular  epithelium. 

The  saccules  of  the  sebaceous  glands  are  invested  by  a  thin  connective 
tissue  tunic  and  a  delicate  basement  membrane.  They  are  embedded  in 
the  subcutaneous  fat  or  in  the  deeper  part  of  the  corium  near  the 
hair  follicle.  The  glands  are  so  disposed  as  to  be  included  within  a 


THE  HAIR 


283 


triangular  space  beneath  the  cor  him,  which  is  bounded  by  the  arrector 
pili  muscle  and  the  hair  follicle.  The  saccules  are  lined  by  several 
layers  of  polygonal  epithelial  cells  the  outermost  of  which  are  cuboidal 
and  rest  upon  the  basement  membrane. 

In  the  peripheral  layers  the  lining  epithelial  cells  multiply  so  actively 
that  the  daughter-cells  are  pushed  inward  until  they  fill  the  entire  sac- 
cule.  During  this  excursion  they  are  progressively  farther  and  farther 

removed  from  their  source  of 
nutrition,  and  as  they  approach 
the  outlet  or  duct  of  the  sac- 
cule,  a  process  of  fatty  degen- 
eration appears  within  the  cell, 


FIG.  277. — SECTION  OF  A  SEBACEOUS  GLAND 
FROM  THE  HUMAN  SCALP,  THROUGH  POINT 
OF  OPENING  INTO  A  HAIR  FOLLICLE 
(OBLIQUELY  CUT). 

Between  the  basement  membrane  of  the 
sebaceous  alveolus  and  the  hair  follicle,  the 
cells  exhibit  successively  later  stages  of  fatty 
degeneration  ending  in  the  formation  of 
sebum.  X  160. 


H& 

FIG.  278. — CELLS  FROM  THE 
CENTRAL  PORTION  OF  THE 
PRECEDING  FIGURE,  SHOW- 
ING Two  SUCCESSIVE  STAGES 
IN  SEBUM  FORMATION  BY 
PROCESSES  OF  FATTY  META- 
MORPHOSES OF  THE  CYTO- 
PLASM. 

Note  the  shrunken  character 
of  the  nuclei  of  the  upper  more 
degenerate  cells.  The  cyto- 
plasm is  filled  with  fat  spher- 
ules. X  550. 


by  which  its  protoplasm  becomes  changed  into  a  granulofatty  mass. 
The  accumulated  product  of  this  degeneration  and  final  disintegration 
of  the  epithelial  cells  forms  the  secretion  of  the  gland.  Continued  cell 
multiplication  at  the  periphery  maintains  the  integrity  of  the  organ. 
19 


290  THE  SKIN 

Sebaceous  glands  of  the  scalp  may  become  cystic  through  occlusion  of 
the  duct  and  form  wens. 

Development. — The  sebaceous  glands  are  developed  as  minute  epithe- 
lial buds  from  the  sides  of  the  hair  columns  or  from  the  deeper  surface 
of  the  epidermis.  These  buds  soon  assume  the  characteristic  flask  shape 
and  later  become  hollowed  out  by  fatty  metamorphosis  of  their  central 
cells.  By  this  process  also  their  lumen  is  eventually  made  continuous 
with  that  of  the  follicle.  Secondary  saccules  of  the  sebaceous  glands  are 
developed  in  a  similar  manner  by  outgrowing  germs  which  appear  near 
the  constricted  neck  portion  of  the  primary  saccule. 


BLOOD  SUPPLY  OF  THE  SKIN 

The  larger  arteries  supplying  the  skin  lie  in  the  subcutaneous  tissue. 
From  these  vessels  branches  pass  toward  the  surface,  giving  off  lateral 
twigs  to  the  rich  capillary  plexuses  in  the  subcutaneous  connective  and 


FIG.  279. — RECONSTRUCTION  OF  THE  CUTANEOUS  BLOOD-VESSELS. 

a,  epidermis;  6,  derma;  c,  subcutaneous  tissue;  d,  deep,  and  e,  superficial  arterial 
plexus;  f-i,  successive  venous  plexuses.     X  9}^.     (After  Spalteholz.) 

adipose  tissues  and  about  the  sweat  glands,  hair  follicles,  and  sebaceous 
glands.  These  arteries  continue  their  course  to  the  deeper  part  of  the 
corium,  where  they  form  an  anastomosing  cutaneous  plexus  of  small 


NEKVE  SUPPLY  291 

vessels.  Branches  from  this  plexus  pass  to  the  papillary  layer,  where  they 
form  a  second  (subpapillary)  plexus  from  which  terminal  arteries  are 
distributed  to  the  capillaries  of  the  papillae. 

The  distribution  of  the  veins  is  similar  to  that  of  the  arteries.  The 
primary  plexus  is  found  in  the  papillary  layer;  occasionally  a  second 
plexus  immediately  underlies  the  first,  and  from  these,  venules  pass  to 
the  deeper  part  of  the  corium,  whence  after  free  anastomosis  they  pro- 
ceed to  the  subcutaneous  tissue,  collecting  on  the  way  the  venules  return- 
ing from  the  hair  follicles  and  secreting  glands,  and  from  the  subcuta- 
neous connective  tissue.  The  very  rich  capillary  network  in  the  papilla 
of  the  hair  bulb  is  worthy  of  special  mention. 

The  lymphatic  vessels  of  the  skin  begin  as  a  terminal  lymphatic 
plexus  in  the  corium,  which  collects  the  lymph  from  the  tissue  spaces 
of  both  derma  and  epidermis.  The  vessels  of  this  plexus  communicate 
with  a  subcutaneous  lymphatic  plexus  of  larger  vessels  which  follow  the 
course  of  the  blood-vessels  on  their  way  to  reach  the  neighboring  groups 
of  superficial  lymph  glands. 


NERVE  SUPPLY 

The  skin  is  abundantly  supplied  with  large  nerve  trunks,  both  sympa- 
thetic and  cerebrospinal  (sensory),  which  find  their  way  along  the  sub- 
cutaneous fat  and  send  branches  directly  to  the  larger  blood-vessels, 
the  hair  follicles,  the  sebaceous  and  sudoriparous  glands,  to  the  cor- 
puscles of  Pacini,  Ruffini,  and  Golgi-Mazzoni,  and  to  the  end  bulbs  of 
Krause,  which  lie  in  the  connective  tissue. 

In  the  cutis  vera  the  nerve  trunks  form  a  plexus  of  delicate  fiber 
bundles  in  the  reticular  layer,  with  a  secondary,  more  closely  meshed 
plexus  of  finer  nerve  bundles  in  the  papillary  layer.  From  these 
plexuses  fibrils  are  distributed  to  the  smaller  blood-vessels  and  to  the 
papillae,  where  many  end  in  tactile  corpuscles.  Other  fibrils  penetrate 
the  epidermis,  terminating  as  naked  fibrils  or  on  tactile  cells. 

In  the  region  of  the  hair  follicle  small  branches  form  a  network 
of  fibrils  in  the  dermal  root  sheath.  Branches  (pilomotor  nerves)  are 
also  distributed  to  the  arrectores  pilorum  muscles. 

In  the  sudoriparous  glands  the  nerves  form  a  fine  plexus  about  the 
membraua  propria  (epilamellar  plexus),  from  which  naked  axis  cylin- 
ders penetrate  the  basement  membrane  and  terminate  between  the 
secreting  cells. 


CHAPTER   XII 
THE  RESPIRATORY   SYSTEM 

The  respiratory  system  may  be  said  to  comprise  a  true  respiratory 
organ,  the  pulmonary  alveoli,  in  which  the  interchange  of  gases  between 
the  air  and  the  blood  occurs,  and  a  system  of  duct-like  passages  leading 


Superior  lurbinate  bone 


Olfactory  nerte 


Nasal  sin 


Sphenoidal  sinus 
Nasal  nerve 


FIG.  280. — PHOTOGRAPH  OF  Azoux  MODEL,  SHOWING  NOSTRIL,  PHARYNX,  LARYNX 

AND  RELATED  STRUCTURES. 

292 


THE  NASAL  CAVITY  293 

thereto,  which,  beginning  with  the  nasal  cavity,  successively  includes 
the  nasopharynx,  larynx,  trachea,  and  bronchi  of  gradually  diminishing 
caliber,  and  which  finally  ends  in  the  terminal  bronchioles  leading  to  the 
air  sacs  and  pulmonary  alveoli. 

The  arrangement  of  these  several  portions  of  the  respiratory  system 
has  been  frequently  compared  to  the  structure  of  the  tubulo-acinar 
glands.  From  this  point  of  view  the  larynx  and  trachea  form  the  duct 
stem  of  the  gland,  the  bronchi  form  the  branching  interlobar  and  inter- 
lobular  ducts,  and  the  terminal  bronchioles  (intercalary  ducts)  end  in 
the  numerous  acinar  air  saccules  of  the  lung. 

Development. — The  original  anlage  of  the  respiratory  system,  begin- 
ning with  the  larynx,  is  a  short  linear  ventromedial  evagination  from 
the  cephalic  end  of  the  primitive  esophagus.  This  trackcal  groove  be- 
comes separated,  distally,  thus  forming  a  tube,  which  grows  backward, 
meanwhile  dividing  distally  into  the  bronchi  which  undergo  further 
division  to  form  the  successively  finer  branches  of  the  pulmonary  system. 
The  respiratory  epithelium  is  thus  of  entodermal  origin,  and  becomes 
enveloped  in  connective  tissue  of  mesodermal  origin. 


THE  NASAL  CAVITY 

This  cavity  is  bounded  by  a  cartilaginous  and  bony  wall  and  is  lined 
by  a  mucous  membrane  which,  according  to  the  nature  of  its  epithelium, 
may  be  divided  into  three  portions:  (1)  the  vestibule,  (2)  the  respira- 
tory portion,  and  (3)  the  olfactory  portion. 

Its  external  and  internal  openings  are  the  nares  and  choance  respect- 
ively. Communicating  with  the  nasal  chambers  are  the  sphenoidal,  maxil- 
lary, frontal,  and  palatal  accessory  sinuses,  and  the  ethmoidal  air  cells. 
Their  lining  membrane  is  continuous  with,  and  histologically  essentially 
like,  though  thinner  than,  that  of  the  respiratory  portion  of  the  nostril. 

THE  VESTIBULE 

The  vestibule  of  the  nose  corresponds  very  closely  to  the  cartilaginous 
portion  of  the  nasal  wall.  Its  mucous  membrane  is  continuous  anteriorly 
with  the  skin  and  posteriorly  with  the  mucous  membrane  of  the  res- 
piratory portion.  The  vestibule  is  lined  by  stratified  squamous  epithe- 
lium, which  offers  a  gradual  transition  from  the  moist  respiratory  epithe- 
lium to  the  dense  horny  epidermis  of  the  skin.  Near  its  external  ori- 


294 


THE  RESPIRATOEY  SYSTEM 


fice  are  numerous  coarse  stiff  hairs,  vibrissw,  connected  with  which  are 
many  sebaceous  glands.  The  vibrissse  have  no  associated  arrectores 
pilorum  muscles.  Some  of  the  glands  also  open  directly  upon  the 
surface  of  the  mucous  membrane. 

The  fibrous  tunica  propria  of  the  vestibule  is  continuous  with  the 
corium  of  the  skin,  and  in  it  are  embedded  the  deeper  portions  of  the 
vibrissffi  and  the  secreting  portions  of  the  sebaceous  glands.  By  its 
deeper  surface  the  tunica  propria  is  closely  attached  to  the  perichon- 
drium  of  those  plates  of  hyaline  cartilage  which  form  the  septum  and 
alae  of  the  nose. 

THE  EESPIRATORY  PORTION 

The  respiratory  portion  of  the  nasal  mucous  membrane  (Schneider- 
ian  membrane)  clothes  the  middle  and  inferior  meatus  of  the  nose.  It 
is  continuous  anteriorly  with  the  mucous  membrane  of  the  vestibule, 


FIG.  281. — FROM  A  SECTION  OF  THE  Mucous  MEMBRANE  OP  THE  RESPIRATORY 
REGION  OF  THE  HUMAN  NOSE. 

a-a,  ciliated  epithelium;  b,  b,  mixed  mucoserous  glands;  c,  blood  vessel.     Hema- 
tein  and  Congo  red.    Photo.     X  185. 


THE  NASAL  CAVITY  295 

above  with  the  olfactory  mucous  membrane,  and  posteriorly  with  that 
of  the  nasopharynx.  The  respiratory  region  is  lined  by  columnar  ciliated 
epithelium  of  the  pseudo-stratified  type,  which  also  contains  many 
mucus-secreting,  goblet-cells. 

The  epithelium  rests  upon  a  distinct  basement  membrane  which 
reacts  to  the  specific  stains  for  elastic  tissue.  The  tunica  propria 
consists  of  a  very  vascular  connective  tissue;  it  varies  much  in  thickness 
in  different  portions.  It  is  thinnest  in  the  accessory  sinuses  and  is  thick- 
est where  it  covers  the  turbinal  bones  and  the  adjacent  portions  of  the 
nasal  septum.  The  tunica  propria  is  richly  supplied  with  both  mucous 
and  serous  glands.  The  smaller  ones,  in  the  thinner  portions  of  the  mu- 
cous membrane,  are  somewhat  convoluted;  the  larger  and  more  numer- 
ous are  tubulo-acinar  glands.  Many  of  the  latter  are  mixed  glands  con- 
taining both  mucous  and  serous  acini.  They  produce  an  abundant  secre- 
tion. 

The  Schneiderian  membrane  is  in  all  portions  extremely  vascular, 
many  of  its  vessels  having  very  thin  walls.  The  thicker  portions  over  the 
turbinals  and  the  septum  are  typically  erectile.  The  dense  connective 
tissue  of  these  portions  is  permeated  with  broad  venous  channels  which 
are  surrounded  by  bands  of  smooth  muscle.  Other  muscular  bundles 
are  longitudinally  distributed.  The  small  arteries  are  contained  within 
the  fibromuscular  stroma. 

The  subepithelial  portion  of  the  tunica  propria  contains  fine  inter- 
lacing bundles  of  connective  tissue  and  many  capillary  blood-vessels. 
Here  and  there  it  is  also  infiltrated  with  lymphocytes  and  occasional 
very  minute  solitary  nodules  are  found.  The  lymphatics  of  the  Schnei- 
derian membrane  lead  posteriorly  to  the  lymph  nodules  of  the  naso- 
pharynx. 

THE  ORGAN  OF  JACOBSON 

Associated  with  the  respiratory  portion  is  the  rudimentary  vomero- 
nasal  organ  (of  Jacobson).  In  the  embryo  of  one  month  it  appears  as 
a  tubular  extension,  one  on  either  side,  into  the  corium  of  the  median 
septum,  opening  anteriorly.  In  transverse  section  it  has  a  semicircular 
outline,  with  its  convexity  mesial.  In  lower  forms,  e.g.,  Amphibia,  it 
persists  in  the  adult  as  a  functionally  important  organ  concerned 
with  smell.  It  is  innervated  by  fibers  from  the  olfactory  nerves,  vomero- 
nasal  nerves,  and  by  the  nervus  terminal-is,  which  is  present  also  in  man 
(Johnston,  Anat.  Eec.,  8,  4,  1914).  In  the  cat  the  tall  columnar  ciliated 
epithelium  (pseudo-stratified)  includes  true  sensory  cells,  similar  to  the 


296 


THE  EESPIEATOEY  SYSTEM 


olfactory  cells.  The  nervus  termiiialis  contains  some  medullated  fibers, 
and  may  contain  both  afferent  and  efferent  components  (Johnston).  In 
the  rabbit  it  innervates  in  addition  to  Jacobson's  organ,  also  a  wide 
area  of  the  nasal  septum  (Huber  and  Guild). 


THE  OLFACTORY  PORTION 

The  olfactory  portion  of  the  nasal  mucous  membrane,  the  olfactory 
organ,  lines  the  superior  meatus,  a  portion  of  the  superior  turbiiiatc 
bone  and  a  corresponding  portion  of  the  median  septum,  and  its 
irregular  border  here  and  there  invades  the  upper  portion  of  the  middle 
meatus.  It  consists  of  a  fibrous  tunica  propria  and  a  clothing  of 


FIG.  282. — THE  OLFACTORY  MUCOSA  OF  A  CAT. 

a,  epithelium;  b,  basement  membrane;  c,  corium;  d,  cuticle;  e,  sustentacular  cell 
layer;/,  olfactory  cell  layer;  g,  basal  cells;  h,  blood-vessel;  i,  a  tubule  of  Bowman's 
glands;  k,  bone.  Hematein  and  picrofuchsin.  Photo.  X  270. 

neuro-epithclium.  The  tunica  propria  contains  elastic  as  well  as  col- 
lagenous  fibers,  and  many  small  tubulo-acinar  serous  glands,  the  olfac- 
tory glands  of  Bowman.  Beneath  the  epithelium  is  an  indistinct  base- 
ment membrane. 


THE  NASAL  CAVITY 


297 


The  neuro-epithelium  contains  three  intermingled  cell  types,  the 
sustentacular,  olfactory,  and  basal  cells. 

The  SUSTENTACULAR  CELLS  are  columnar  ciliated  epithelial  cells 
which  possess  a  distinct  cuticular  margin.  Their  nuclei  are  ovoid,  and, 
since  they  lie  at  the  same  level,  they  form  a  continuous  superficial  zone 
of  oral  nuclei.  The  deep  ends  of  the  cells  are  often  branched;  they 
interlace  with  one  another  and  with  the  processes  of  the  olfactory  and 


-sr 


FIG.  283. — THE  OLFACTORY  Mucous  MEMBRANE. 

a,  duct  of  gland;  b,  basal  cells;  c,  cuticular  border  with  olfactory  cilia;  k,  nuclei 
of  the  sustentacuLir  cells;  k',  nuclei  of  the  olfactory  cells;  r,  layer  of  olfactory  cells; 
s,  corium,  containing  connective  tissue  cells  and  nerve  fibers;  st,  sustentacular 
cells.  X  465.  (After  Kolliker.) 

basal  cells.    The  cytoplasm  of  the  sustentacular  cells  is  finely  granular 
and  contains  a  yellow  pigment. 

The  OLFACTORY  CELLS  occupy  a  unique  position  among  neuro-epithe- 
lial  cells  in  that  they  are  true  nerve  or  ganglion  cells.  They  possess  a 
small  cytoplasmic  body  and  two  processes,  a  distal  and  a  central.  Their 
nuclei  are  spherical  and  are  disposed  in  several  rows  beneath  the  nuclear 
zone  of  the  sustentacular  cells ;  thus  they  form  a  broad  zone  of  spherical 
nuclei.  The  distal  process  of  the  olfactory  cell  projects  as  a  slender 
filament  whose  free  end,  carrying  several  fine  cilia,  reaches  the  surface  of 


298 


THE  RESPIEATOEY  SYSTEM 


the  membrane  through  a  pore-like  opening  in  the  cuticular  membrane 
which  is  formed  by  the  cuticle  of  adjacent  sustentacular  cells.  The 
central  process  of  the  olfactory  cell  penetrates  to  the  tunica  propria  and 
becomes  a  non-medullated  nerve  fiber  of  one  of  the  many  rami  of  the 
olfactory  nerve ;  it  passes  to  the  olfactory  bulb,,  where  its  terminal  arbori- 
zation with  the  dendrites  of  the  mitral  cells  forms  the  olfactory  glom- 
eruli. 

The  BASAL  CELLS  are  flattened  cells  which  form  the  deepest  nuclear 
zone  of  the  olfactory  neuro-epithelial  layers.     Their  cytoplasm  is  finely 

granular  and  their  nu- 
clei are  ovoid  or  flat- 
tened. Frequently  they 
send  a  short  process  be- 
tween the  branched  ends 
of  the  sustentacular  cells. 
Many  small  nerve 
trunks  occur  in  the 
tunica  propria.  The 
great  majority  of  these 
are  non-medullated  and 
are  formed  by  the  cen- 
tral processes  of  the  ol- 
factory cells,  which  proc- 
esses are  true  axons. 
Several  of  the  smaller 
superficial  fiber  bundles 
unite  in  the  deeper  part 
of  the  tunica  propria  to 
form  one  of  the  small 
olfactory  nerves.  Taken 

together,  about  twenty  in  number  on  each  side,  these  form  two  olfac- 
tory nerves,  unique  among  cerebrospinal  nerves  in  being  collectively 
non-medullated.  A  few  medullated  fibers,  derived  from  the  trigeminus, 
are  also  found  in  the  tunica  propria ;  they  distribute  their  terminal  vaso- 
motor  branches  to  the  blood-vessels,  and,  by  fine  sensory  filaments  which 
end  between  the  epithelial  cells,  supply  the  neuro-epithelial  layer.  The 
trigeminus  fibers  supply  a  similar  innervation  to  the  respiratory  mucosa. 
The  blood  vessels  of  the  olfactory  mucous  membrane  are  abundant. 
Their  capillary  plexiises  form  several  layers  in  the  tunica  propria,  and 
their  veins  mostly  empty,  through  the  ethmoidal  veins,  into  the  superior 


FIG.  284. — VERTICAL  SECTION  OF  THE  OLFACTORY 
MUCOSA  OF,  A  KITTEN. 

a,  deep,  and  b,  superficial  border  of  the  epithe- 
lium; c,  olfactory  cells;  d,  sustentacular  cells;  g,  ol- 
factory nerve  fibers  in  the  corium  of  the  mucosa. 
Golgi  stain.  X  325.  (After  Kolliker.) 


THE  NASOPHAKYNX 


299 


longitudinal  sinus — a  most  significant  fact.  On  the  other  hand  the 
veins  of  the  respiratory  region  return  their  blood  to  the  internal  maxil- 
lary vein,  while  some  of  those  of  the  vestibule  anastomose  with  the  radi- 
cals of  the  facial  vein  which  supply  the  adjacent  skin. 


ofy 


FIG.  285. — DIAGRAM  OF  THE  RELATIONS  OF  THE  NEURONS  OF  THE  OLFACTORY  NERVE 
AND  OLFACTORY  BULB. 

olf.  c.,  olfactory  nerve  cells,  located  in  the  olfactory  region  of  the  nasal  mucosa, 
whose  axons  enter  the  olfactory  nerve,  olf.  n.,  and  terminate  in  relation  with  the 
dendrites  of  the  mitral  cells,  me.,  in  the  olfactory  glomeruli,  gl.  The  axons  of  the 
mitral  cells,  a.,  enter  the  olfactory  tract,  where  they  make  a  sharp  bend  and  pass 
toward  the  cerebrum  giving  off  frequent  collaterals.  At  n'  a  nerve  fiber  appears 
to  end  by  a  free  ramification  among  the  mitral  cells  of  the  olfactory  bulb.  (After 
Schafer.) 

The  lymphatics  of  the  olfactory  region  can  be  readily  injected  from 
IV  sub-dural  spaces  of  the  meninges.  They  form  a  network  in  the  con- 
nective tissue  of  the  tunica  propria. 


THE  NASOPHARYNX 


This  cavity,  like  that  of  the  nose,  is  limited  by  a  bony  wall.  Its 
mucous  membrane  is  continuous  anteriorly  with  that  of  the  respiratory 
portion  of  the  nose,  and  posteriorly  with  that  of  the  oropharynx.  The 


300  THE  KESPIRATORY  SYSTEM 

structure  of  its  mucous  membrane  resembles  that  of  the  Schneiderian 
membrane,  but  its  dorsal  wall,  in  addition  to  the  ciliated  epithelium,  the 
thin-walled  blood-vessels,  and  the  numerous  secreting  glands,  contains 
many  small  nodules  of  lymphoid  tissue.  These  nodules  form  a  consider- 
able mass,  the  pharyngeal  tonsil. 

The  ciliated  epithelium  of  the  nasopharynx  is  also  continuous  with 
the  lining  epithelium  of  the  auditory  (Eustachian)  tube.  The  tunica 
propria  is  firmly  adherent  to  the  bony  wall  of  the  dorsal  surface,  but  is 
more  loosely  attached  laterally  and  ventrally  to  the  pharyngeal  and 
palatine  muscles. 

THE  LARYNX 

The  wall  of  the  larynx  is  formed  by  several  large  plates  of  hyaline 
cartilage — thyroid,  cricoid,  and  arytenoid  cartilages — which  are  firmly 
united  by  ligamentous  bands  of  fibrous  tissue;  the  cartilaginous  wall  in- 
closes a  mucous  membrane  of  considerable  thickness. 

The  larger  cartilages  are  of  the  hyaline  variety  and  are  prone  to 
ossify  in  adult  life.  The  tips  of  the  arytenoids,  the  cornicula  of  San- 
torini,  the  cuneiform  cartilages  of  Wrisberg,  and  the  epiglottis  are  of 
the  elastic  variety  of  cartilage,  and,  though  frequently  much  infiltrated 
with  fat,  are  not,  like  the  hyaline  cartilages,  subject  to  ossification.  The 
median  portion  of  the  thyroid  cartilage  is  also  generally  elastic  in  char- 
acter; this  portion  does  not  generally  ossify  in  women.  In  the  lateral 
hyothyroid  ligaments  are  the  minute  triticeous  cartilages,  generally 
hyaline  but  occasionally  fibrous  in  character. 

The  intrinsic  muscles  of  the  larynx,  taking  origin  from  these  car- 
tilages, pursue  their  course  beneath  the  mucous  membrane. 

The  upper  portion  of  the  larynx,  including  the  greater  part  of  the 
epiglottis,  as  far  as  the  false  vocal  cords  is  lined  by  stratified  squamous 
epithelium  which  is  continuous  with  that  of  the  pharynx. 

The  epithelium  of  the  vocal  cords  and  that  covering  the  anterior 
surface  of  the  arytenoids  is  also  of  the  stratified  squamous  variety. 
The  remaining  portions  of  the  larynx,  including  the  base  of  the  epiglottis 
on  its  laryngeal  surface,  the  ventricle,  and  the  entire  portion  below  the 
level  of  the  true  vocal  cords,  are  lined  by  columnar  ciliated  epithelium 
of  the  pseudo-stratified  type.  The  ciliary  motion  is  directed  toward  the 
pharynx.  The  epithelium  rests  upon  a  basement  membrane  which  is 
less  highly  developed  than  in  other  portions  of  the  respiratory  tract. 

The  tunica  propria  consists  of  fibro-elastic  connective  tissue  in  which 


THE  LARYNX 


301 


arc  many  small  tubulo-acinar  mucous  glands.  These  are  most  abun- 
dant in  the  region  of  the  ventricle  and  the  false  vocal  cords.  In  this 
region  also  there  is  much  diffuse  lymphoid  tissue,  and  the  lateral  and 
dorsal  wall  contains  several  solitary  nodules  which  are  so  constant  in 
their  appearance  as  to  warrant  designating  them  laryngeal  tonsil' 
( Frankel ) .  Occasionally,  however, 
lymph  nodules  are  not  present  in  the 
mucous  membrane  of  the  human 
larynx.  The  deeper  portion  of  the 
tunica  propria  in  certain  parts,  e.g.,  in 
the  false  vocal  cords,  contains  a  few 
striped  muscle  fibers  in  addition  to  those 
of  the  named  muscles  of  the  larynx.  The 
false  vocal  cords  and  the  aryteno-epi- 
glottic  folds  contain  loose  fibrous  tissue 
and  frequently  much  fat. 

The  true  vocal  cords  are  formed  by 
dense  bands  of  elastic  and  a  few  col- 
lagenous  fibers  which  .are  covered  by  a 
mucosa  clothed  with  stratified  squamous 
epithelium.  Their  free  margin  is  sharp- 
ly defined;  at  their  attached  margin, 
however,  they  blend  indistinctly  with 
the  tunica  propria.  The  free  margin  of 
the  vocal  cords  has  no  connective  tissue 
papillae  on  the  surface  of  the  tunica 
propria,  but  toward  the  trachea  super- 
ficial papillae  of  connective  tissue  pro- 
ject into  the  deeper  surface  of  the 
stratified  epithelium. 

The  mucous  membrane  of  the  larynx 
is  freely  supplied  with  blood-vessels 

and  lymphatics.  The  latter  terminate  in  the  deep  cervical  lymph 
nodes.  The  nerve  fibers  form  an  abundant  plexus  in  the  laryngeal 
mucosa,  from  which  motor  fibers  are  distributed  to  the  muscles  and 
sensory  fibers  to  the  epithelium.  The  latter  end  in  fine  fibrils  between  the 
cells  of  the  lining  epithelium.  In  the  stratified  squamous  epithelium, 
especially  that  of  the  epiglottis,  small  taste  buds  are  also  found;  none, 
however,  occur  on  the  vocal  cords. 


FIG.  286. — A  VERTICAL  SECTION 

THROUGH    THE    LATERAL    WALL 

OF  THE  HUMAN  LARYNX. 

a,  cartilage;  6,  laryngeal  mucosa, 
clothed  with  ciliated  epithelium; 
c,  transection  of  the  vocal  cord,  in 
this  region  the  mucosa  is  clothed 
with  stratified  epithelium ;  d,  ducts 
of  mucous  glands;  e,  lymphoid 
nodule;  /,  muscle;  g,  mucous 
glands;  h,  submucosa;  i,  blood- 
vessel; V,  ventricle  of  the  larynx. 
Hematein  and  eosin.  Photo.  X  8. 


302  THE  KESPIEATOEY  SYSTEM 


THE  TRACHEA 

The  trachea  proper  extends  from  the  lower  border  of  the  cricoid  car- 
tilage to  the  point  where  it  bifurcates  into  the  two  primary  bronchi,  a 
distance  of  about  four  and  one-half  inches.  The  wall  of  the  trachea 
somewhat  resembles  that  of  the  larynx.  It  consists  of  three  layers : 

1.  The  mucous  membrane,  or  mucosa. 

2.  The  submucosa. 

3.  The  fibrocartilaginous  coat,  or  adventitia. 

'    The  mucous  membrane  presents  slight  longitudinal  folds,  and  is 
lined  by  columnar  ciliated  epithelium,  like  that  of  the  larynx,  which 


IV 


FIG.  287. — TRANSECTION  OF  THE  WALL  OF  A  CHILD'S  TRACHEA. 

7,  mucosa;  II,  submucosa;  ///,  cartilage;  IV,  outer  fibrous  coat;  a,  columnar 
ciliated  epithelium;  b,  tunica  propria;  c,  layer  of  elastic  fibers;  d,  mucous  glands; 
e,  perichondrium.  Hematein  and  eosin.  Photo.  X  90. 

rests  upon  a  delicate  basement  membrane.  The  tunica  propria  includes 
a  thin  inner  layer  of  connective  tissue  which  is  richly  supplied  with 
small  blood-vessels  and  infiltrated  by  many  lymphocytes,  and  an  outer 


THE  TRACHEA 


303 


layer  of  elastic  tissue  most  of  whose  fibers  are  longitudinally  disposed. 
The  elastic  layer  begins  in  the  region  of  the  vocal  cords  in  the  larynx 
and  is  continuous  below  with  the  similar  layer  of  the  bronchial  mucous 
membrane.  Elastic  fibers  are  more  numerous  in  the  trachea  of  the  lower 
mammals  than  in  that  of  man.  A  muscularis  mucosa,  a  characteristic 
structure  of  the  mucosa  of  the  digestive  tube, 
is  lacking  in  the  trachea.  The  elastic  mem- 
brane occupies  the  position  held  by  the  mus- 
cularis mucosa  in  other  organs. 

The  submucosa  consists  of  loose  areolar 
tissue  which  contains  many  small  tubulo-acinar 
mucous  glands.  The  ducts  of  these  glands 
penetrate  the  mucosa  and  open  upon  the  free 
surface  of  the  trachea.  They  supply  an  abun- 
dant mucous  secretion.  This  coat  also  contains 
the  larger  blood-vessels  and  nerves  which  are 
destined  for  the  supply  of  the  mucosa. 

The  fibrocartilaginous  coat  is  formed  by 
the  C-shaped  'ring  cartilages'  of  the  trachea 
(from  sixteen  to  twenty  in  number)  which  are 
firmly  united  to  one  another  by  ligamentous 
membranes  of  fibrous  tissue  continuous  with 
the  perichondrium  of  adjacent  cartilage  plates. 
The  cartilages  are  of  the  hyaline  variety  and 
are  subject  to  more  or  less  ossification  as  age 
advances.  They  rarely  overlap  each  other,  so 
that  but  a  single  plate  of  cartilage  forms  the 
wall  at  any  given  point.  Their  borders  are 
irregular,  and  horizontal  sections  near  the 

upper  or  lower  margin  of  the  cartilage  frequently  pass  through  several 
projections,  which,  unless  properly  interpreted,  would  lead  one  to  infer 
that  the  cartilaginous  plate  was  interrupted.  . 

The  interval  between  the  ends  of  the  C-shaped  cartilage  plates  is 
occupied  by  a  membrane  of  smooth  muscle  whose  transverse  fibers  unite 
the  adjacent  ends  of  the  cartilages.  The  muscle  fibers  are  inserted  into 
the  perichondrium  of  the  cartilages.  Many  of  the  fibers  are  obliquely, 
and  a  few  of  the  outermost  are  longitudinally,  disposed.  This  muscular 
portion  of  the  tracheal  wall  forms  the  so-called  track ealis  muscle.  The 
mucous  membrane  and  submucosa  of  this  portion  of  the  trachea  are  un- 
usually thick  and  their  mucous  glands  are  exceptionally  large.  The 


FIG.  288.— MUCUS-SE- 
CRETING, TUBULO  -  AL- 
VEOLAR GLAND  OF  THE 
HUMAN  TRACHEAL  MU- 
COSA. 

The  terminal  dark  areas 
are  demilunes.  Recon- 
struction. X  200.  (After 
Maziarski.) 


304  THE  RESPIRATORY  SYSTEM 

loose  fibrous  tissue  which  invests  the  outer  surface  of  the  cartilaginous 
coat  contains  many  small  sympathetic  nerve  trunks  and  ganglia. 


THE  LUNG 

At  the  root  of  the  lung  the  trachea  divides  into  a  primary  bronchus 
for  each  lung.  By  repeated  subdivisions — the  earliest  branches  being 
given  off  at  acute  angles,  the  later  ones  at  more  obtuse  angles — the 
smaller  and  smaller  bronchi  finally  end  in  minute  terminal  bronchioles 
which  lead  through  the  alveolar  ducts  to  the  pulmonary  air  sacs  and 
alveoli.  One  may  thus  distinguish  between  primary,  secondary,  and 
tertiary  bronchi,  and  bronchioles.  The  mode  of  division  for  the  main 
series  of  bronchi  is  monopodial,  of  the  smaller  bronchi  a  mixed  dichot- 
omy and  monopody  (Miller,  Jour.  Morph.,  24,  4,  1913).  According  to 
Piersol  the  bronchioles  are  the  branches  of  the  fourth  or  fifth  order. 

BRONCHI 

The  wall  of  the  primary  bronchi  is  similar  in  structure  to  that  of 
the  trachea,  but  in  bronchial  tubes  which  are  one  or  two  divisions 
removed  (secondary  and  tertiary  bronchi)  from  the  primary  bronchi 
the  plates  of  cartilage  are  no  longer  C-shaped,  and  a  complete  muscularis 
mucosas,  within  the  cartilages,  forms  the  outermost  boundary  of  the 
mucous  membrane.  In  such  tubes — typical  bronchi — the  wall,  as  in  the 
trachea,  comprises: 

1.  A  mucosa. 

2.  A  submucosa. 

3.  A  fibrocartilaginous  coat. 

The  mucosa,  a  continuation  of  that  of  the  trachea,  is  lined  by 
tall,  columnar,  pseudo-stratified,  ciliated  epithelium  which  rests  upon  a 
distinct  elastic  basement  membrane.  The  epithelium  is  thrown  into 
wavy  longitudinal  folds.  The  tunica  propria  is  extremely  vascular;  it 
possesses  an  abundant  supply  of  thin-walled  veins  of  small  caliber,  to- 
gether with  many  lymph  vessels.  Its  connective  tissue  forms  a  delicate 
fibrous  reticulum  in  the  meshes  of  which  are  many  lymphocytes.  The 
outer  portion  of  the  tunica  propria  contains  bundles  of  fine  longitudinal 
elastic  fibers,  which  form  a  complete  layer  about  the  tube.  This  elastic 
layer  is  thickest  opposite  the  ridges  and  thinnest  opposite  the  troughs  of 
the  epithelial  waves. 

The   outer   boundary   of   the    mucous   membrane    contains    a   well- 


THE  LUNG 


305 


FIG.  289. — A  BRONCHUS  FROM  THE  HUMAN  LUNG. 

a,  lining  epithelium;  b,  duct  of  a  mucous  gland;  c,  muscularis  mucosso;  d,  accu- 
mulated mucus,  etc.,  bathing  the  surface  of  the  epithelium;  e,  mucous  glands;  /, 
hyaline  cartilage;  g,  outer  fibrous  coat;  h,  pulmonary  alveoli.  Hernatein  and  eosin. 
Photo.  X  34. 


developed  muscularis  mucosce  composed  of  interlacing  bundles  of  circular 
smooth  muscle  fibers.    This  layer  forms  a  complete  muscular  coat  which 


306  THE  KESPIRATOKY  SYSTEM 

is  here  and  there  pierced  by  the  ducts  of  mucous  glands  whose  secreting 
portions  lie  in  the  submucosa. 

The  submucosa,  by  its  broad-meshed  areolar  tissue,  loosely  unites 
the  mucous  membrane  to  the  cartilage  plates.  This  coat  contains  the 
larger  blood-vessels,  nerves,  and  lymphatics  which  are  distributed  to  the 
mucosa.  It  also  contains  the  secreting  portions  of  many  tubulo-acinar 
mucous  glands,  which  occur  in  groups  that  in  the  larger  bronchi  almost 
completely  surround  the  tube.  The  number  and  size  of  these  glands  is 
in  direct  proportion  to  the  size  of  the  bronchus.  The  efferent  ducts  of 
the  mucous  glands  penetrate  the  muscularis  mucosae  and  open  upon  the 
free  surface  in  the  interval  between  adjacent  folds  of  the  epithelial  lining. 
In  the  tunica  propria  the  ducts  possess  ampullary  dilatations  which  are 
lined  by  ciliated  cells  and  contain  portions  of  the  mucous  secretion. 

The  fibrocartilaginous  coat  is  formed  by  a  dense  fibrous  membrane 
in  which  the  cartilages  are  embedded.  The  plates  of  hyaline  cartilage 
vary  much  in  number  and  size,  being  more  or  less  highly  developed  in 
proportion  to  the  size  of  the  bronchial  tube.  They  possess  at  all  times 
a  somewhat  crescentic  shape.  In  the  larger  bronchi  three  or  four  car- 
tilage plates  with  overlapping  edges  encircle  the  entire  tube.  In  the 
lower  mammals,  e.g.,  the  pig,  these  overlapping  cartilages  are  so  highly 
developed  that  the  plates  often  lie  three  or  four  deep;  in  man  they  are 
rarely  more  than  one  or  two  deep.  As  the  bronchi  diminish  in  size  by 
division,  the  cartilage  plates  are  no  longer  of  sufficient  size  to  completely 
encircle  the  wall  but  leave  broad  intervals  in  which  this  coat  is  only 
represented  by  fibrous  tissue.  In  tubes  of  a  diameter  of  0.8  to  1  milli- 
meter, bronchioles,  the  cartilages  entirely  disappear,  and  in  these  or  some- 
what smaller  bronchioles  the  mucous  glands  are,  likewise,  110  longer 
found.  According  to  Cutore  (Anat.  Anz.,  47,  13,  1914),  the  cartilage 
plates  of  the  intrapulmonary  bronchi  contain  elastic  fibers,  and  are  in 
fact  true  elastic  cartilages. 

The  outer  surface  of  the  cartilages  is  invested  with  a  clothing  of 
loose  fibrous  tissue  of  varying  thickness — sometimes  known  as  the  outer 
fibrous  coat — in  which  the  branches  of  the  pulmonary  artery  and  veins 
and  also  many  nerve  trunks  and  ganglia  are  found.  In  the  larger  bronchi 
the  two  vessels,  pulmonary  artery  and  pulmonary  vein,  are  found  on 
opposite  sides  of  the  tube;  in  the  bronchioles  only  one  vessel,  the  artery, 
is  in  relation  with  the  tube,  the  vein  pursuing  an  independent  course 
within  the  pulmonary  tissue. 

Near  the  root  of  the  lung  many  small  lymph  nodes  are  found  in  the 
outer  fibrous  coat.  In  the  smaller  bronchi  these  are  represented  by 


THE  LUNG 


307 


solitary  nodules  which,  it  is  important  to  note,  are  always  found  in 
the  fibrous  connective  tissue  which  forms  the  outer  portion  of  the 
bronchial  wall.  The  bronchial  lymph  nodes  and  nodules  are  deeply 
pigmented,  the  volume  of  the  pigment  being  dependent  upon  the  age 
and  occupation  of  the  individual.  It  is  apparently  derived  by  absorption 
from  the  surface  of  the  bronchi  and  is  therefore  absent  in  infancy,  defi- 
cient in  youth,  abundant  in  adult  life,  and  especially  abundant  in  those 
individuals  whose  occupations  have  necessitated  the  inhalation  of  a  dusty 
atmosphere. 

THE  BRONCHIOLES 

The  bronchioles  possess  neither  cartilage,  mucous  glands,  nor 
lymph  nodules.  Their  epithelium,  though  still  ciliated,  is  low — short 
columnar,  or,  in  the  smaller  bronchioles,  cuboidal.  The  tunica  propria 
contains  many  lym- 
phocytes and  the 
elastic  tissue  forms 
an  almost  complete 
layer  of  longitudi- 
nal elastic  fibers. 

The  muscularis 
mucosae  is  relatively 
more  highly  devel- 
oped than  in  the 
larger  bronchi ;  it 
completely  encircles 
the  wall  and  is  in- 
vested with  an  ad- 
ventitious layer  of 
fibrous  tissue  which 
contains  the  small 
arteries,  nerves, 
lymphatics,  a  capil- 
lary plexus  with 

b.r.,  respiratory  (terminal)  bronchiole;  d.  al.,  alveolar 
duct;  a,  atria;  s.  al.,  alveolar  or  air  sac;  a.p.,  pulmonary 
alveoli;  art.,  pulmonary  artery;  v.,  pulmonary  vein.  (After 
Miller.) 


FIG.  290. — DIAGRAM  OF  PAIMAUY  LOBULE  OF  LUNG 
(Luxe  UNIT). 


elongated  meshes, 
and  occasional  ven- 
ules. 

The  fibrous  coat 

of  the  bronchiole  here  and  there  blends  with  the  fibrous  bands  of  inter- 
lobular  tissue  and  is  in  contact  with  the  adjacent  pulmonary  alveoli. 


308 


THE  RESPIRATORY  SYSTEM 


Each  bronchiole  enters  the  apex  of  a  pulmonary  lobule  (secondary)  and 
divides  into  terminal  so-called  respiratory  bronchioles  (terminal  bron- 
chioles). 


Fia.  291. — FROM  A  SECTION  or  A  CHILD'S  LUNG. 

B,  bronchiole  in  transection,  with  its  adjacent  pulmonary  artery,  A;  TB,  bron- 
chiole, ending  in  a  terminal  bronchiole,  from  which  are  derived  the  alveolar  duct,  7, 
the  atrium,  A,  and  the  pulmonary  alveoli,  PA.  In  the  center  of  the  figure  a  pul- 
monary alveolus,  PA,  is  seen  in  transection;  many  similar  ones  are  shown.  Hema- 
tein  and  eosin.  Photo.  X  45. 


The  respiratory  bronchiole  bears  alveoli  which  become  more  numer- 
ous toward  its  distal  end.  It  thus  contains  a  variable  epithelial  lining 
consisting  proximally  of  a  low  columnar,  sometimes  ciliated,  epithelium, 
with  distally  a  more  flattened  non-ciliated  type,  and  in  the  alveoli  a 
typical  greatly  flattened  respiratory  epithelium  including  non-nucleated 


THE  LUNG 


309 


plates.  It  has  a  diameter  of  0.5  millimeter  or  less.  The  epithelium 
rests  upon  a  thin  nbroinuscular  coat,  the  continuation  of  the  mucous 
membrane  of  the  bronchioles.  The  muscle  still  forms  an  almost  com- 
plete though  very  thin  investment  of  circular  fibers;  the  muscle  fibers, 


a 


FIG.  292.  —  FROM  A  SECTION  OF  A  CHILD'S  LUNG. 

a,  a  small  tertiary  bronchus;  b,  bronchioles;  c,  bronchioles  ending  in  terminal 
bronchioles,  alveolar  ducts,  etc.;  d,  terminal  bronchioles  in  transection,  they  have 
a  more  regular  contour  and  thicker  wall  than  the  alveoli;  e,  pulmonary  arteries; 
/,  a  bronchial  artery;  g,  a  bronchial  vein;  h,  interlobular  fibrous  septum.  Hematein 
and  eosin.  Photo.  X  62. 

however,  are  not  continued  into  the  wall  of  the  pulmonary  air  sacs.  The 
elastic  fibers,  derived  from  the  elastic  layer  of  the  bronchioles,  pass  over 
to  the  alveolar  walls  in  which  they  form  a  delicate  network. 

The  respiratory  bronchioles  are  short  branching  tubules  leading  to 


310 


THE  RESPIRATORY  SYSTEM 


broader  spaces,  the  alveolar  ducts  (infundibula  of  Schultze),  which  are 
surrounded  by  air  saccules  with  pulmonary  alveoli.  According  to  Miller 
the  alveolar  ducts  bear  numerous  alveoli,  and  are  lined  with  flattened 
respiratory  epithelium,  and  contain  scattered  bundles  of  smooth  muscle 
which  end  in  a  delicate  sphincter  where  the  duct  passes  into  the  non- 


FIG.  293. — FROM  A  SECTION  OF  A  CHILD'S  LUNG. 

A,  atrium;  B,  bronchioles  ending  in  terminal  respiratory  bronchioles,  TB;  PA, 
pulmonary  artery;  PV,  pulmonary  vein.    Hematein  and  eosin.    Photo.     X  50. 

muscular  atria,  from  three  to  six  for  each  alveolar  duct.  Each  atrium, 
of  more  or  less  circular  outline,  opens  into  a  variable  number  (two  to 
five)  of  irregular  and  variable  alveolar  saccules  (air  sacs).  Each  sac- 
cule  bears  on  its  periphery  numerous  pulmonary  alveoli.  The  epithelium 
of  the  entire  bronchial  tree,  including  the  nucleated  respiratory  cells,  con- 
tains abundant  mitochondria  (Meves  and  Tsukaguchi,  Anat.  Anz.,  46, 
1,  1914). 


THE  LUNG 

THE  PULMONARY  ALVEOLI 


311 


The  pulmonary  alveoli  are  minute  air  cells,  open  toward  the  alveolar 
ducts,  whose  extremely  thin  wall  consists  of  a  capillary  network,  a  deli- 


FIG.  294. — DIAGRAM  OF  THE  THREE  PULMONARY  LOBULES  CONNECTED  WITH  A 
TERMINAL  BRONCHIOLE   (TB). 

The  middle  lobule  is  stippled.  BR,  bronchiole ;.RB,  respiratory  bronchiole  of 
the  first  order;  TB,  respiratory  bronchiole  of  the  second  order  (terminal  bronchiole); 
/,  II,  III,  alveolar  ducts;  /,  2,  and  3  a,  b,  c  and  d,  atria;  As,  alveolar  sacs  with 
pulmonary  alveoli  or  air  cells.  (Adapted  from  Miller,  Jour.  Morph.,  20,  4,  1913.) 


cate  fibre-elastic  reticulum,  and  a  lining  epithelium.  The  alveoli  are 
so  densely  clustered  about  the  alveolar  duct  that  the  capillary  plexus,  in 
the  form  of  a  reticulated  membrane  of  wide  capillary  vessels,  is  exposed 
to  the  air  of  two  adjacent  alveoli,  being  separated  therefrom  only  by  its 
own  endothelium  and  the  epithelial  lining  of  the  alveolus. 


312 


THE  EESPIRATORY  SYSTEM 


y&T  A  f        m 

®Vv«     ?4  f*-l 

v~  ••*«;£•**"" 

FIG.  295. — Two  ALVEOLI  OF  \  CHILD'S  LUNG. 

In  A,  the  wall  is  cut  across  and  viewed  in  profile;  B,  a 
tangential  section  showing  the  cup-shaped  bottom  of 
the  alveolus  and  the  pulmonary  epithelium  in  surface 
view;  c,  a  pulmonary  venule.  Hematein  and  eosin.  X 
425. 


The  lining  epithelium  of  the  alveoli,  continuous  through  the  alveolar 

ducts  with  that  of  the  respiratory  bronchioles,  consists  of  flattened  cells 

and  broad  protoplasmic  non-nucleated  plates.    These  cells  are  narrower 

A  B  and  thicker   (cubi- 

-.-'&/  -  ,  cal)  in  the  prenatal 

*^  --^***.'  ^  ^       g$*j£  •-.  lung  and  when  the 

;/  !    ^  ^|$  •%  lung    is    collapsed, 

§.&  broader    and    thin- 

*     ®  ^  ner  wlicn  it  is  fully 

*$  expanded.        The 

^M  fl  completely  expand- 

ed alveolus  in  full 
respiration  is  two 
to  three  times  the 
size  of  the  collapsed 
or  retracted  alveo- 
lus of  full  expira- 
tion (Kolliker). 
The  elastic  fibers  of 
the  alveolar  wall 
form  a  delicate  net 

among  the  capillaries;  in  the  meshes  of  this  net  a  few  white  fibers  are 
found.  The  normal  respiratory  epithelium  does  not  become  phagocytic 
(Miller,  1911). 

An  alveolar  duct  with  its  atria,  alveolar  saccules,  blood-vessels,  lymph- 
vessels  and  nerves  forms  a  natural  unit  of  structure,  the  primary  pul- 
monary lobule. 

Pores  leading  from  one  alveolus  to  another  have  been  described,  but 
Miller  denies  their  presence  in  the  lung  of  the  cat  (Jour.  Morph.,  24,  4, 
1913). 

THE  PLEURA 

The  pleura  is  a  serous  membrane  whose  visceral  layer  (pleura  pul- 
monalis)  envelops  the  lung,  and  whose  parietal  layer  (pleura  costalis, 
diaphragmatis  et  mediastinalis)  lines  the  thoracic  cavity. 

The  surface  of  the  pleura  is  clothed  with  a  layer  of  mesothelium 
which  rests  upon  a  'subserous'  layer  of  connective  tissue.  The  mesothe- 
lium contains  frequent  'stomata'  which  in  the  costal  pleura  are  only 
present  over  the  intercostal  spaces. 


THE  LUNG 


313 


These  pleural  pores  have  been  the  subject  of  considerable  discussion. 
They  have  been  regarded  by  some  as  giving  direct  vent  to  lymphatics; 
but  Walters  (Anat. 
Hefte,  Bd.  46,  1913)  has 
quite  conclusively  shown 
that  they  are  artifacts,  an 
interpretation  maintained 
also  by  Miller. 

The  connective  tissue 
contains  an  abundant 
network  of  elastic  fibers. 
It  is  loosely  attached  to 
the  chest  wall  but  is  more 
firmly  united  to  the  pul- 
monary tissue.  Normally 
the  pleura  contains  no 
lymph  nodes  (Miller). 

The  pleura  contains 
many  small  blood-vessels 
and  an  abundant  plexus 
of  blood  and  lymphatic 
capillaries.  Its  innerva- 
tion  includes  both  sym- 
pathetic and  cerebral  (vagus)  fibers.  Both  are  apparently  non-medul- 
lated.  The  sympathetic  nerve  fibers  are  supplied  to  the  walls  of  the 
blood  vessels;  they  are  vasomotor  in  function.  The  vagus  fibers  are  sen- 
sory in  nature,  and  terminate  in  lamellar  corpuscles,  and  as  fine  free 
sensory  fibers. 


FIG.  296. — TRANSECTION  OF  THE  PLEURA  OF  AN 
INFANT. 

a-a,  layer  of  mesothelium;  6,  submesothelial  con- 
nective tissue;  c,  pulmonary  alveoli;  d,  a  small  blood- 
vessel. Hematein  and  eosin.  Photo.  X  470. 


FIG.  297. — FROM  A  SECTION  OF  THE  PLEURA  OF  MAN. 

The  elastic  tissue  appears  black,     a-a,  mesothelial  surface;  6-6,  submesothelial 
connective  tissue.    Weigert's  elastic  tissue  stain,  hematein  and  picrofuchsin.     X  110. 


314  THE  RESPIRATOEY  SYSTEM 

THE  LOBULE  OF  THE  LUNG 

If  carefully  examined,  the  surface  of  the  pulmonary  pleura  presents 
minute  polygonal  areas  (10  to  25  mm.  in  diameter),  the  bases  of  the 
anatomical  (or  secondary)  lobules,,  whose  borders  mark  the  attachment 
of  fine  bands  of  interlobular  connective  tissue,  outlined  by  pigmented 
lines.  In  microscopical  preparations  still  finer  bands  may  be  found, 
which  traverse  the  pulmonary  tissue  in  the  direction  of  the  root  of  the1 
lung,  and  which  partially  outline  minute  conical  areas,  the  true  pul- 
monary (or  primary)  lobules,  or  lung  units,  whose  bases  are  directed 
toward  the  pleura,  and  their  apices  toward  the  root  of  the  lung.  In  many 
of  the  lower  mammals,  e.g.,  ox,  these  lobules  are  more  distinctly  outlined 
by  interlobular  connective  tissue  than  is  the  case  in  man. 

At  the  apex  of  the  secondary  lobule  a  small  bronchiole  (intralobular 
bronchiole)  enters  and  divides  into  its  respiratory  bronchioles  (from  30 
to  100).  This  secondary  pulmonary  lobule  consists  of  a  collection  of 
the  smaller  units  or  primary  pulmonary  lobules  above  described.  At 
the  same  point  a  terminal  branch  of  the  pulmonary  artery  enters  with 
the  bronchiole  and  supplies  the  anastomosing  capillary  plexus  in  the 
alveolar  walls.  Branches  of  the  bronchial  artery  do  not  supply  any  of 
the  primary  intralobular  structures,  and  the  pulmonary  veins  which 
return  the  blood  from  the  alveolar  capillaries  arise  at  the  periphery  of 
the  primary  lobule  and  immediately  enter  the  interlobular  connective 
tissue. 

The  interlobular  connective  tissue  contains  the  smaller  branches  of 
the  pulmonary  veins,  the  lymphatics  returning  from  the  pleura,  and 
the  non-medullated  nerve  trunks  which  are  destined  for  the  supply  of 
the  pleura  and  the  intralobular  pulmonary  tissue. 

BLOOD  SUPPLY  or  THE  LUNGS 

The  blood  supply  of  the  lungs  is  derived  from  two  distinct  sources, 
the  pulmonary  arteries  and  the  bronchial  arteries.  The  former  is  des- 
tined chiefly  for  aeration  in  the  capillaries  of  the  alveolar  walls,  the 
latter  for  the  nutrition  of  the  bronchial  walls. 

The  pulmonary  artery  enters  at  the  hilum  in  company  with  the 
vein  and  the  bronchus.  It  follows  the  bronchus  throughout  its  course 
and  gives  an  arterial  branch  to  each  of  its  subdivisions.  The  large  ar- 
teries nearly  equal  in  size  the  bronchus  in  relation  to  which  they  lie, 
but  the  smaller  branches  are  not  more  than  one-fourth  to  one-fifth  the 


THE  LUNG 


315 


diameter  of  their  bronchus.  Throughout  their  course  the  branches  of 
the  pulmonary  arteries  lie  on  the  wall  of  the  bronchi,  viz.,  in  the  outer 
fibrous  coat  or  attached  thereto  by  a  broad  band  of  fibrous  tissue.  More- 


FIG.  298. — FROM  THE  LUNG  op  A  CHILD. 

At  a,  the  origin  of  a  pulmonary  venule  in  the  wall  of  a  lobule  is  shown;  at  6,  the 
pulmonary  venule  is  just  coming  into  relation  with  the  bronchiole.  Hematein, 
Weigert's  elastic  stain,  and  picrofuchsin.  Photo.  X  105. 

over  each  bronchus  is  accompanied  by  only  one  branch  of  the  pulmonary 
artery  and  receives  no  capillaries  from  it. 

At  the  apex  of  the  secondary  pulmonary  lobule  the  pulmonary  artery 
enters  with  the  bronchiole ;  it  resolves  into  smaller  arterioles  correspond- 
ing in  number  approximately  to  the  number  of  respiratory  bronchioles, 
each  of  which  again  breaks  into  several  small  twigs — one  for  each  atrium, 
according  to  Miller — which  supply  the  capillary  networks  in  the  walls  of 
the  alveolar  ducts  and  alveoli.  The  pulmonary  capillaries  form  an  ex- 


316 


THE  EESPIRATOEY  SYSTEM 


ceedingly  dense  net  of  anastomosing  vessels  in  the  walls  of  the  alveoli, 
the  meshes  of  the  capillary  net  being  frequently,  in  the  deeper  portions 
of  the  lung,  of  less  diameter  than  the  vessel  itself.  At  the  periphery  of 
the  lobule  the  capillaries  converge  to  form  several  venules  which  unite 
to  form  larger  veins  in  the  interlobular  tissue.  These  veins  pursue  an 


FIG.  299. — FROM  THE  LUNG  OF  A  DOG  WHOSE  BLOOD-VESSELS  HAD  BEEN  INJECTED 
WITH  A  GELATINOUS  MASS,  AND  APPEAR  BLACK. 

The  outlines  of  the  pulmonary  alveoli  and  atria  are  well  shown.  Many  of  the 
alveoli  have  been  cut  tangentially  and  present  a  surface  view  of  the  capillary  net- 
work; in  others  the  alveolar  wall  is  cut  across  and  is  seen  in  profile.  X  '125. 

independent  course  and  are  always  found  at  a  considerable  distance  from 
the  bronchioles  and  lobular  branches  of  the  pulmonary  artery.  (See 
Fig.  290.) 

The  smaller  branches  of  the  pulmonary  artery  near  the  surface  of 
the  lung  give  arterial  twigs  to  the  adjacent  portions  of  the  pleura. 
From  the  capillaries  of  the  pleura  minute  venules  enter  the  interlobular 
tissue  and  join  the  interlobular  veins. 


THE  LUNG 


317 


The  interlobular  veins  (pulmonary  veins)  follow  the  fibrous  septa 
toward  the  hilum.  They  soon  come  into  relation  with  the  bronchi  and 
are  then  found  on  that  side  of  the  bronchus  opposite  the  pulmonary 
artery.  The  vein,  like  the  artery,  lies  outside  of  the  bronchial  wall  in 
the  adjacent  fibrous  tissue.  It  is,  as  a  rule,  only  those  bronchi  whose 
wall  contains  cartilage  plates  which  are  in  relation  with  both  pulmonary 
artery  and  vein;  the  smaller  bronchioles  are  usually  accompanied  by  the 
artery  only.  Those  veins  which  accompany  the  bronchi  receive  smaller 
branches  from  the  bron- 
chial wall  and  by  union 
with  their  fellows  form 
larger  and  larger  vessels 
which  finally  make  their 
exit  as  the  pulmonary 
veins  and  pass  to  the  left 
auricle  of  the  heart. 

The  bronchial 
arteries  also  follow  the 
bronchial  tubes  in  all 
their  ramifications.  The 
larger  branches  are  found 
in  the  outer  fibrous  coat 
near  the  cartilages,  the 
smaller  ones  lie  in  the 
submucous  and  mucous 
coats.  In  contradistinc- 
tion to  the  pulmonary 
vessels  the  bronchial  ar- 
teries are  found  in  the 
wall  of  the  bronchi,  not 

outside  of  the  bronchial  wall.  They  supply  capillaries  to  all  of  the  tis- 
sues of  the  bronchi.  The  bronchial  capillaries  reunite  to  form  small 
venules  whose  course  differs  with  the  size  of  the  tube.  In  the  terminal 
bronchioles  these  venules  pass  directly  to  the  interlobular  veins,  and, 
according  to  Miller,  the  pulmonary  veins  receive  a  similar  acquisition 
at  each  division  of  the  bronchi.  In  the  larger  bronchi,  however,  the 
venules  unite  within  the  bronchial  wall  to  form  the  radicals  of  the  bron- 
chial vein  which,  lying  in  the  fibrous  tissue  of  the  bronchial  walls,  re- 
trace the  course  of  the  bronchi  to  the  hilum,  where  they  make  their  exit 
as  the  bronchial  veins  and  join  the  azygos  veins.  Thus,  only  the  walls 


FIG.  300. — FROM  THE  CENTRAL  PORTION  OF  THE 
PRECEDING  FIGURE. 

a,  two  pulmonary  alveoli  in  transection;  b,  tan- 
gential section  showing  the  bottom  of  an  alveolus; 
c,  a  minute  pulmonary  venule.  Photo.  X  500. 


318  THE  KESPIRATOEY  SYSTEM 

of  the  larger  bronchial  tubes  are  supplied  with  bronchial  blood,  and, 
according  to  Schaffer,  a  few  branches  at  the  root  of  the  lung  are  also 
distributed  to  the  adjacent  pleura.  Many  of  the  bronchioles,  the  res- 
piratory bronchioles,  and  also  the  alveolar  ducts,  pulmonary  alveoli,  and 
the  pleura  all  receive  their  nutrition  from  the  pulmonary  arteries. 
Finally  it  may  be  said  that  there  are  no  anastomoses  between  the  pul- 
monary arteries  and  veins  except  among  the  capillaries  of  the  alveolar 
walls. 

LYMPHATICS 

The  pulmonary  lymphatics  form  a  plexus  in  the  walls  of  the  bronchi 
and  bronchioles,  penetrating  to  the  mucous  membrane.  Branches  from 
this  plexus  frequently  anastomose  with  perivascular  lymphatic  vessels 
about  the  branches  of  the  pulmonary  artery  and  veins.  A  close  network 
of  lymphatic  vessels  is  also  found  in  the  pleura,  its  efferent  vessels  passing 
into  the  interlobular  tissue  to  join  those  vessels  which  accompany  the 
veins.  The  pulmonary  lymphatics  are  supplied  with  frequent  valves  and 
numerous  anastomoses.  At  the  atria  the  lymphatics  pass  to  the  inter- 
lobular septa,  so  that  the  alveolar  walls  lack  lymph  vessels. 

The  lymphatic  vessels  of  the  bronchi  are  connected  with  larger  lym- 
phatic vessels  of  the  outer  fibrous  coat  and  with  the  lymph  nodules  in 
the  walls  of  the  larger  tubes.  Many  of  the  larger  vessels  in  the  outer 
fibrous  coat  of  the  bronchi,  and  also  those  which  accompany  the  pul- 
monary artery,  enter  those  lymph  nodes  which  are  in  relation  with  the 
bronchial  walls  at  the  root  of  the  lungs.  The  pleural  lymphatic  plexus 
arid  the  vessels  accompanying  the  pulmonary  veins,  after  pursuing  much 
of  their  course  through  the  interlobular  connective  tissue  in  company 
with  the  pulmonary  veins,  also  open  into  the  bronchial  lymph  nodes. 
Much  pigment  is  conveyed  through  these  vessels  and  is  deposited  in  (a) 
the  interlobular  connective  tissue,  (&)  the  fibrous  tissue  about  the  pul- 
monary arteries,  and  most  abundantly  in  (c)  the  bronchial  lymph 
nodules  and  nodes. 

Lymphoid  tissue  forms  an  important  constituent  of  the  lungs,  serv- 
ing as  filters  in  the  lymph  circulation  and  as  centers  to  which  the 
phagocytes  carry  their  collected  material.  It  occurs  as  nodes,  nodules, 
or  as  smaller  masses  of  more  diffuse  lymphoid  tissue;  it  may  be  peri- 
bronchial,  periarterial,  perivenous  or  subpleural  in  position.  Lymph 
nodes  are  associated  with  the  larger  divisions  of  the  bronchi  and  located 
at  the  points  of  branching.  The  smaller  masses  are  found  in  greatest 


THE  LUNG  319 

numbers  at  the  periphery  of  the  primary  and  secondary  lobules  (Miller, 
Anat.  Rec.,  5,  3,  1911). 

NERVE  SUPPLY 

The  nerves  of  the  lungs  are  derived  from  the  anterior  and  posterior 
pulmonary  plexuses  of  the  sympathetic  system.  They  are  distributed 
to  the  walls  of  the  blood-vessels,  where  they  form  a  delicate  plexus  with 
terminal  fibrils  among  the  smooth  muscle  fibers,  and  to  the  walls  of  the 
bronchial  tubes.  Small  nerve  trunks,  with  which  many  minute  ganglia 
are  connected,  occur  in  large  numbers  in  the  outer  fibrous  coat  of  the 
bronchi. 

From  these  nerve  trunks  and  ganglia  fibrils  are  distributed  to  the 
bronchial  mucous  membrane,  in  which  they  supply  the  muscularis 
mucosae,  and  form  a  terminal  plexus  beneath  the  epithelial  coat.  These 
fibers  have  been  traced  to  the  respiratory  bronchioles,  where  they  are 
said  to  form  a  delicate  plexus  within'  the  lobule  in  the  interalveolar  walls 
(Wolff,  Arch.  f.  Anat.,  1902).  Sensory  fibrils  are  supplied  by  the  vagus 
nerve.  The  vagus  contributes  to  the  bronchi  and  their  subdivisions  also 
motor  fibers,  for  the  most  part  probably  indirectly  through  the  sym- 
pathetic ganglia. 


CHAPTER    XIII 
THE   DIGESTIVE    SYSTEM 

The  digestive  system  includes  the  cavities  of  the  mouth,  pharynx, 
esophagus,  stomach,  and  intestines,  together  with  the  accessory  glands — 
the  salivary  glands,  pancreas,  and  liver.  Associated  with  the  mouth 
and  cooperating  in  the  function  of  the  essential  organs  of  digestion  are 
also  the  teeth  and  the  tongue. 


THE  MOUTH 

The  walls  of  the  oral  cavity  comprise  a  mucous  membrane,  a  sub- 
mucous  layer  of  connective  tissue,  and  a  muscular  or  bony  paries. 

The  mucous  membrane  (mucosa)  is  clothed  with  a  layer  of  strati- 
fied squamous  epithelium  which  presents,  at  the  margin  of  the  lips, 
a  gradual  transition  to  the  epidermis  of  the  skin,  and  at  the  fauces  is 
continuous  with  the  lining  epithelium  of  the  faucial  isthmus  and  the 
pharynx. 

The  tunica  propria  (corium,  stratum  proprium)  upon  which  the 
epithelium  rests,  consists  of  dense  areolar  tissue,  the  superficial  portion 
of  which  specially  abounds  in  elastic  fibers.  This  portion  of  the  corium 
consists  of  rather  delicate  connective  tissue  bundles  which  at  frequent 
intervals  are  prolonged  into  the  epithelial  coat  in  the  form  of  minute 
conical  papilla,  similar  to  those  of  the  skin,  whose  height  varies  with 
the  location.  The  tallest  papilla  are  found  on  the  gums  and  at  the 
margins  of  the  lips,  the  lowest  on  the  inner  surface  of  the  cheeks  and 
the  soft  palate. 

The  papillary  layer  of  the  corium  contains  a  plexus  of  capillary  blood- 
vessels which  is  connected  with  a  network  of  small  arteries  and  veins  in 
the  deeper  part  of  the  tunica  propria. 

The  submucosa  consists  of  looser  connective  tissue  which  blends 
insensibly  with  that  of  the  mucosa,  and  unites  the  mucous  membrane 
to  the  subjacent  muscles  and  bones  forming  the  wall  of  the  oral  cavity. 
In  most  portions  the  buccal  mucous  membrane  is  but  loosely  connected 

320 


THE  MOUTH 


321 


with  the  underlying  parts,  but  in  the  hard  palate  and  the  gums  this 
union  is  very  firm. 

Lymphoid  tissue  occurs  in  considerable  abundance  in  the  oral  mu- 
cous membrane.  Areas 
of  diffuse  lymphoid 
tissue  are  of  frequent 
occurrence  and  small 
lymph  nodules  are  oc- 
casionally found.  The 
lymphatic  vessels  form 
a  plexus  in  the  tunica 
propria,  which  empties 
into  larger  vessels  in 
the  submucosa. 

Secreting  glands 
occur  in  considerable 
abundance  in  all  por- 
tions of  the  buccal 
mucous  membrane  ex- 
cept that  covering  the 
gums.  The  glands  are 
of  the  tubulo-acinar 
type  and  produce 
either  a  pure  mucous 
secretion  or,  in  the 
case  of  the  larger  ones, 
a  mixed  mucous  and 
serous  secretion.  The 
ducts  of  the  glands  are 
lined  by  columnar 
cells  which,  near  the 
mouth  of  the  duct,  of- 
fer a  gradual  transi- 
tion to  the  stratified  squamous  epithelium  of  the  mucosa.  The  glandular 
epithelial  cells  of  the  secreting  portions  become  swollen  and  clear  after  a 
period  of  rest,  but  are  shrunken  and  present  a  faint  cytoplasmic  reticu- 
lum  after  activity.  The  different  glands  of  the  same  region,  and  even 
different  cells  in  the  same  gland,  often  exhibit  various  stages  of  secretory 
activity.  The  fundus  of  the  secreting  glands  frequently  extends  into  the 
loose  connective  tissue  of  the  submucosa.  At  the  margin  of  the  lips  and 
21 


a  c        d     b 

FIG.  301. — FROM  A  SECTION  THROUGH  THE  LIP  OF 
AN  INFANT. 

a,  cutaneous  surface;  b,  epithelium  of  the  oral  mu- 
cosa; c,  layer  of  striated  muscle;  d,  layer  of  mucous 
glands.  Hematein  and  eosin.  Photo.  X  10 


322 


THE  DIGESTIVE  SYSTEM 


more  rarely  in  the  neighboring  portions  of  the  huccal  mucous  membrane 
are  small  sebaceous  glands  which  open  directly  upon  the  free  surface. 
The  oral  glands  will  be  further  described  below  under  salivary  glands. 


FIG.  302. — AXIAL  SECTION  OP  A  HUMAN  MOLAR  TOOTH. 
C,  cementum;  D,  dent  in;  P,  pulp  cavity;  S,  enamel.     X  8.     (After  Sobotta.) 


THE  TEETH 


323 


THE  TEETH 


STRUCTURE 


Each  tooth  rests  in  a  bony  socket  in  the  alveolar  process  of  the  maxil- 
lary bone,  and  is  also  held  in  place  by  the  periosteum  of  the  alveolar 
sac  and  the  adjacent  portion  of  the  gum.  The  tooth  is  divisible  into  a 
free  portion  or  crown,  and  a  concealed  portion  or  root  which  usually 
consists  of  from  one  to  three  fangs.  The  slightly  constricted  border 
between  the  root  and  the 
crown,  which  is  surrounded  by 
the  soft  tissues  of  the  gum,  is 
known  as  the  neck  of  the  tooth. 

The  tooth  consists  of  a  su- 
perficial calcareous  portion  and 
a  central  medulla,  the  dental 
or  pulp  cavity,  which  occupies 
the  axis  of  the  tooth  and  which 
contains  a  peculiar  embryonal 
type  of  connective  tissue,  very 
similar  to  reticular  tissue,  the 
dental  pulp.  At  the  tip  of 
each  fang  is  an  opening,  the 
foramen  apicis  dentis,  leading 
to  a  narrow  canal  which  pene- 
trates the  wall  of  the  tooth  and 
permits  the  entrance  of  the 
nerves  and  blood-vessels  Avhich 
supply  the  pulp. 

The  calcareous  wall  of  the 
tooth  is  formed  by  three  dis- 
tinct tissues:  (1)  dentin  or 

ivory;  (2)  enamel;  (3)  cementum.  The  dentin  incloses  the  entire  pulp 
cavity  and  is  in  turn  covered  by  the  enamel  and  cementum,  the  enamel 
forming  the  superficial  layer  of  the  crown,  the  cementum  that  of  the 
root  of  the  tooth. 

The  Dental  Pulp. — The  dental  pulp  is  an  embryonal  type  of  con- 
nective tissue  which  is  rich  in  branching  stellate  cells  and  poor  in 
fibers.  It  contains  no  elastic  fibrils,,  and  the  delicate  collagenous  fibers 


Contour  lines  of  Retzius 


(  Prism  stripes  of 
\     Schreger 


Contour   lines  of 
Owen 


Dentinal  tubules 

Granular  layer  of 
Tomes 

Incremental  lines  of 
Schreger 


loot  canal 


FIG.  303. — DIAGRAM  OF  AN  AXIAL  GROUND 
SECTION  OF  TOOTH,  SHOWING  THE  SEV- 
ERAL STRIPES  OF  THE  DENTIN  AND  THE 
ENAMEL. 


324 


THE  DIGESTIVE  SYSTEM 


instead  of  forming  bundles  are  arranged  in  an  interlacing  network,  the 
fine  fibrils  of  which  are  in  intimate  relation  with  the  connective  tissue 

cells.  It  according- 
ly closely  resembles 
reticular  connective 
tissue.  The  stellate 
connective  tissue 
cells  are  scattered 
throughout  the  en- 
tire pulp,  but  at  the 
periphery  of  the 
cavity  are  closely 
crowded  and  are 
much  enlarged. 
These  peripheral 
cells  form  a  layer 
o  f  odontoblasts 
which  is  in  contact 
with  the  dentin. 

The  odonto- 
blasts are  cylindri- 
cal branched  con- 
nective tissue  cells 
whose  long  axis 
(about  40  p.)  is 
perpendicular  t  o 
the  surface  of  the 
adjacent  dentin. 
From  their  apex  a 
delicate  process  is 
sent  into  the  den- 
tinal  canals,  in 
which  they  fre- 
quently extend  all 
the  way  through 
the  dentin.  Lat- 
eral processes  from 
the  cell  bodies  of  the  odontoblasts  interlace  with  each  other  and  firmly 
unite  the  cells  into  a  membranous  layer.  Other  processes  are  given  off 
irom  the  base  of  these  cells  and  intermingle  with  the  fibers  of  the  pulp, 


FIG.  304. — FROM  A  LONGITUDINAL  SECTION  OF  THE  NECK 
OF  A  CHILD'S  TOOTH  AND  THE  ADJACENT  ALVEOLUS. 

a,  enamel;  b,  cementum;  c,  dentin;  d,  bone;  e,  peri- 
osteum;/, corium;  g,  lymphoid  tissue;  //,,  stratified  epithe- 
lium of  the  gum;  i,  circular  dental  ligament;  k,  epithelial 
remnants;  /,  blood-vessels.  X  25.  (After  Kolliker.) 


THE  TEETH  325 

• 

so  that  if  this  tissue  is  forcibly  separated  from  the  dentin  the  odonto- 
blasts  remain  adherent  to  the  connective  tissue  of  the  pulp.  The  nuclei 
of  the  odontoblasts  are  found  near  their  inner  or  basal  extremity.  Their 
cytoplasm  is  of  considerable  extent  as  compared  with  that  of  the  other 
connective  tissue  cells  of  the  pulp. 

The  dental  pulp  is  richly  supplied  with  blood-vessels,  derived  from 
a  nutrient  artery  which  enters  through  the  root  canal,  its  several 
branches  forming  a  network  of  minute  arterioles  and  capillary  vessels 
in  the  center  of  the  pulp  cavity,  and  a  peripheral  close-meshed  capil- 


FIG.  305. — FROM  A  SECTION  OP  A  HUMAN  TOOTH  WHICH  HAD  BEEN  GROUND  TO 
EXTREME  THINNESS. 

o,  dentin;  b,  granular  layer  of  Tomes;  c,  enamel.     Photo.     X  150. 

lary  network  which  is  in  close  relation  with  the  layer  of  odontoblasts. 
Numerous  delicate  lymphatic  vessels,  uniting  to  leave  the  root  as  one 
or  several  large  vessels,  have  also  recently  been  demonstrated  in  the  tissue 
of  the  dental  pulp  (Schweitzer). 

A  rich  nerve  supply  is  derived  from  fine  branches  which  also  enter 
by  the  root  canal.  Most  of  the  nerve  fibers  lose  their  myelin  sheaths 
soon  after  they  enter  the  pulp.  They  form  a  primary  plexus  in  the 
connective  tissue  from  which  fine  fibers  pass  to  the  periphery  and 
form  a  marginal  plexus  beneath  the  odontoblasts.  From  here  delicate 
terminal  sensory  fibrils  ramify  over  the  odontoblasts  and  pass  in  great 
abundance  into  the  dentinal  tubules,  usually  two  to  each  tubule  (Mum- 
mery, Proc.  K.  Soc.,  Series  B,  85,  1912).  This  peripheral  distribution 
of  nerve  fibrils  explains  the  extreme  sensitiveness  of  the  dentin.  Sympa- 
thetic fibers  supply  the  muscle  cells  of  the  pulp  arterioles. 

Dentin. — The  dentin  surrounds  the  entire  pulp  cavity  except  at 
the  opening  of  the  root  canal.  It  is  a  fine  calcareous  substance  which 
resembles  bone  in  that  it  consists  of  a  collagenous  fibrous  matrix  and 
is  infiltrated  with  lime  salts.  The  matrix  is  a  fine  fibrous  network  of 


326 


THE  DIGESTIVE  SYSTEM 


dense  connective  tissue,  the  majority  of  whose  fibers  are  disposed  in  a 
longitudinal  direction.    The  meshes  of  the  matrix  are  almost  completely 

^— ^==rrrs^^        filled  by  a   deposit  of  calcareous  salts 

which  gives  the  dentin  its  bony  consis- 
tence. Dentin  consists  of  about  28  per 
cent,  organic  and  72  per  cent,  earthy 
matter.  The  latter  includes  calcium 
phosphate,  about  67 'per  cent.;  calcium 
carbonate,  about  3  per  cent.;  and  mag- 
nesium phosphate,  Avith  a  trace  of  cal- 
cium fluorid. 

Here  and  there,  especially  toward  its 
peripheral  border  and  near  the  apex  of 
the  tooth,  the  dentinal  matrix  fails  to 
become  calcified.  Such  uncalcified  areas, 
interglobular  spaces,  are  encroached  upon 
by  the  rounded  or  globular  margins  of 
the  adjacent  calcified  matrix  Avhich 
forms  the  so-called  dentinal  globules. 

The  dentin  is  everywhere  permeated 
by  a  system  of  canaliculi,  the  dentinal 
tubules  or  canals,  which  extend  in  a  ra- 
dial manner  from  the  pulp  cavity  out- 
ward to  the  cementum  and  enamel 
Their  course  is  characteristically  curved, 
resembling  the  letter  s.  The  cavity  of 
the  dentinal  tubules  is  partially  occupied 
by  the  dentinal  processes  (fibers)  of  the 
odontoblasts,  an  arrangement  which  may 
be  compared  to  that  existing  between  the 
processes  of  the  bone  cells  and  the  canal- 
iculi of  bone.  At  their  inner  extremity 
the  dentinal  tubules  are  2  to  4  /*  in  di- 
ameter, but  they  taper  very  gradually, 


FIG.  306. — SECTION  OF  FANG 
PARALLEL  TO  THE  DENTINAL 
TUBULES,  HUMAN  CANINE. 
(Waldeyer). 

1,  cementum,  with  large 
lacunse,  canaliculi  and  indica- 
tions of  lamellae;  2,  granular 
layer  of  Tomes  with  large  in- 
terglobular  spaces;  3,  dentinal 
tubules.  X  300.  (From  Quain's 
"Anatomy.") 


especially  in  the  outer  portion  of  their  course,  where  they  finally  reach  a 
diameter  of  no  more  than  0.5  to  1  /*. 

The  dentinal  tubules  may  divide  dichotomously  in  the  inner  third  of 
their  course;  beyond  this  point  they  give  off  very  fine  lateral  twigs, 
which  at  first  leave  the  parent  tubule  nearly  at  right  angles,  but  later 
are  slightly  inclined  outward.  At  their  distal  end  iriost  of  the  dentinal 


THE  TEETH 


327 


tubules  divide'  into  a  group  of  terminal  branches,  some  of  the  arboriza- 
tions being  very  extensive,  others  consisting  of  but  two  or  three  sub- 
divisions. The  coarser  branches  are  frequently  looped,  the  distal  end  of 
the  loop  often  anastomosing  with  adjacent  tubules.  In  their  course 
through  the  dentin  those  canaliculi  which  enter  the  larger  iiiterglobular 
spaces  are  continued  through  these  spaces  without  interruption. 

The  walls  of  the  dentinal  tubules  are 
formed  by  extremely  dense  calcareous  den- 
tinal xlicalhs  (of  Neumann)  which  are  very 
resistant  to  the  action  of  acids.  The  curva- 
tures in  the  course  of  the  dentinal  tubules 
are  of  two  types ;  the  longer  primary  curves 
and  the  shorter  spiral  secondary  curves. 
They  occur  with  extreme  regularity  and  as 
a  result  give  rise  to  certain  parallel  lines 
in  the  substance  of  the  dentin  which  follow 
the  contour  of  the  dentinal  surface.  These 
are  known  as  the  incremental  lines  of 
Schreger. 

A  second  system  of  dentinal  striae,  vis- 
ible in  ground  sections  of  tooth  under  low 
magnification,  are  the  contour  lines  of 
Owen  (arched  incremental  lines  of  Salter). 
They  run  nearly  parallel  to  the  lines  of 
Schreger  in  the  crown  and  toward  the  tip 
of  the  root,  but  elsewhere  cut  these  lines  at 
wide  angles  (Fig.  303).  They  represent 
lines  of  defective  calcification  between  suc- 
cessively deposited  layers  of  dentin. 

The  superficial  portion  of  the  dentin  is  formed  by  the  granular  layer 
of  Tomes,  in  which  there  are  no  dentinal  tubules,  but  instead  there  are 
in  this  layer  numerous  small  interglobular  spaces  from  which  minute 
canaliculi  radiate  in  various  directions.  Many -of  these  canaliculi  are 
connected,  on  the  one  hand  with  the  dentinal  tubules,  and  on  the 
other  with  the  canaliculi  and  bony  lacuna?  of  the  cementum.  The 
canaliculi  of  the  granular  layer  are  readily  distinguished  from  the  ad- 
jacent dentinal  tubules  by  the  extreme  irregularity  of  their  course,  which 
contrasts  sharply  with  the  straight  or  regularly  curved  course  of  the 
dentinal  tubules. 

The  granular  layer  is  relatively  thick  in  the  root  of  the  tooth,  but 


FIG.  307. — DENTIN  FROM  A 
GROUND  SECTION  OF  A  HU- 
MAN MOLAR,  SHOWING  THE 
DENTINAL  TUBULES  Cur 
ACROSS. 

The  tubules  appear  as  dark 
round  or  oval  areas  in  the  den- 
tinal matrix.  Each  tubule  is 
surrounded  by  a  narrow  lighter 
halo,  corresponding  to  the 
sheath  of  the  tubule,  perhaps 
an  optical  effect.  X  750. 


328  THE  DIGESTIVE  SYSTEM 

becomes  much  thinner  toward  the  neck.  Beneath  the  enamel  it  becomes 
so  thin  that  toward  the  apex  of  the  tooth  it  is  scarcely  demonstrable.  At 
this  point  also,  occasional  dentinal  tubules  are  continued  for  a  short 
distance  into  the  enamel,  though  this  condition  is  more  characteristically 
developed  in  some  of  the  lower  mammals  (e.g.,  Rodentia)  than  in  man. 
Enamel. — The  enamel,  which  covers  the  exposed  crown  of  the  tooth, 
is  the  hardest  tissue  of  the  body.  About  90  per  cent,  of  its  earthy  matter 
is  calcium  phosphate;  about  4  per  cent,  is  calcium  carbonate;  less  than 

5  per  cent,  of  its  substance  consists  of  organic  matter. 

It  contains  a  slightly  larger  trace  of  calcium  fluorid 

than  dentin. 

Its  unit  of  structure  is  a  calcareous  cylinder,  the 

enamel  prism.     These  prisms  or  'fibers'  radiate  out- 

ward  from  the  dentin  and  are  disposed  after  the 
FIG.  308. — ENAMEL      manner  of  a  mosaic.    They  are  firmly  united  to  each 
PRISMS  IN  THAN-      O^QT  ^  &  yery  ^in  jayer  of  caicjfie(j  inter  prismatic 

cement  substance.     They  represent  calcified  colum- 
From   the   tooth 

of  a  calf,     x  350.     nar  ectodermal  cells. 
(After  Kolliker.)  In  transverse  section  the  enamel  prisms  have  a 

polygonal,  frequently  quite  regular  hexagonal,  out- 
line. In  certain  bundles,  especially  toward  the  periphery,  the  prisms  have 
the  shape  in  transverse  outline  of  stout  crescents.  In  longitudinal  view 
the  prisms  present  a  slightly  beaded  appearance,  the  constricted  portions 
being  darker  and  delicately  cross-striped.  This  peculiar  structure  and 
optical  condition  results  from  the  manner  of  the  formation  of  the  prisms 
by  the  deposition  of  successive  globules  of  preenamel  substance,  subse- 
quently becoming  calcified  to  form  definitive  enamel.  The  enamel  cement 
exhibits  a  reciprocal  beading.  Since  the  external  surface  of  the  enamel  is 
greater  than  the  internal,  and  since  the  enamel  prisms  are  of  approx- 
imately uniform  diameter  throughout,  additional  shorter  prisms,  pointed 
at  their  inner  end,  are  interpolated  toward  the  surface.  The  striped  and 
beaded  character  of  the  enamel  prisms  is  especially  conspicuous  in  the 
teeth  of  rodents. 

The  enamel  prisms  are  grouped  into  bundles  within  which  the  con- 
stituent prisms  are  parallel.  The  course  of  the  prism  bundles,  however, 
is  variable,  so  that,  though  following  a  more  or  less  radial  course  through 
the  enamel,  the  prism  bundles  frequently  cross  one  another  at  acute 
angles.  In  axial  longitudinal  sections  of  ground  tooth  this  crossed  ar- 
rangement of  the  prism  bundles  produces  the  appearance  of  radially 
disposed  alternating  dark  and  light  bands.  This  banding  is  seen  under 


THE  TEETH 


329 


low  magnification,  and  is  especially  conspicuous  in  reflected  light;  it  is 
due  to  the  difference  with  which  the  groups  of  transverse  and  longitudi- 
nally cut  enamel  prisms  reflect  the  rays  of  light.  The  dark  bands  are 
known  as  the  radial  lines,  or  the  prism  stripes  of  Schreger. 

Ground  sections  of  dried  tooth  show  also  brownish  lines  in  the  enamel 
having  an  arrangement  approximately  parallel  with 
the  surface  of  the  tooth.  These  contour  lines  of 
Rctzius  are  explained  by  von  Ebner  as  the  result  of 
air-filled  fissures  in  the  dried  enamel.  They  are  also 
said  to  be  the  result  of  the  wavy  direction  of  the 
enamel  prisms.  They  are  most  probably  caused  by 
imperfect  calcification,  marking  growth  stages  in  the 
development  of  the  enamel. 

Cementum. — The  dental  cement,  or  crusta  pe- 
trosa,  is  a  thin  layer  of  bony  tissue  which  invests  the 
root  of  the  tooth.  It  forms  a  very  thin  layer  at  the 
neck  of  the  tooth,  but  gradually  increases  in  thick- 
ness as  it  approaches  the  tip  of  the  fang. 

The  cementum  consists  of  parallel  layers  of  bony 
lamella?  between  which  many  lacunas  with  their  bone 
corpuscles  are  included.  Bone  canaliculi  radiate 
from  the  lacunae  and  frequently  open  into  the  inter- 
globular  spaces  of  the  granular  layer.  There  are  no 
ITaversian  systems  in  the  cementum,  but  the  thicker 
portions  are  frequently  penetrated  by  vascular  canals 
which,  like  Volkmamrs  canals,  are  not  accompanied 
by  concentric  lamellae.  The  cementum  is  firmly 
united  to  the  granular  layer  of  the  dentin,  the  matrix 
of  the  two  tissues  being  continuous. 

The  cementum  is  invested  with  a  periosteal  coat, 
the  periodontium,  pericementum,  alveolar  periosteum, 
or  root  (peridenlal)  membrane,  of  dense  fibrous  tissue  which,  at  the  neck 
of  the  tooth,  unites  with  the  dense  connective  tissue  of  the  gum  to  form 
an  annular  thickening  of  very  dense  fibrous  tissue  which  encircles  the 
tooth  and  is  known  as  the  circular  dental  ligament.  The  root  membrane 
contains  no  elastic  fibers,  but  sends  considerable  numbers  of  slender 
white  fibrous  bands  (Sharpey's  fibers}  into  the  cementum.  These  bands 
effect  a  firm  anchorage  of  the  tooth  to  the  alveolar  wall.  They  are  anal- 
ogous to  the  perforating  fibers  of  Sharpey  which  bind  the  periosteum  to 
the  osseous  lamella?. 


Fic.309.— A  GROUP 

OFENAMEL 

PRISMS  CUT  LON- 

GITUDINALLY 
FROM  THE  INCI- 
SOR TOOTH  OF 
THE  RAT,  SHOW- 
ING THEIR  IR- 
REGULARLY 
BEADED  CHARAC- 
TER AND  THE 

CROSS  STRIA- 

TIONS. 

Shorter  and  slen- 
derer priems  are 
interpolated  periph- 
erally. X  375. 


330 


THE    DIGESTIVE  SYSTEM 
;  b 


FIG.  310. — FKOM  A  SECTION  OF  A  HUMAN  TOOTH  WHICH  HAD  BEEN  GROUND  TO 
EXTREME  THINNESS. 

a,  dentin;  6,  granular  layer  of  Tomes;  c,  cementum.    Photo.     X  140. 


DEVELOPMENT  OF  THE  TEETH 

The  teeth  arise  in  part  from  the  ectodermal  epithelium  of  the  oral 
cavity  and  in  part  from  the  mesenchyma  of  the  alveolar  processes.  In 
the  seventh  week  of  fetal  life  there  appears  upon  the  surface  of  the 
maxillary  ridges  a  thickening  of  the  epithelium  which  grows  into  the 
subjacent  mesenchyma  "in  the  form  of  a  longitudinal  plate  or  shelf, 
the  labiodental  strand,  whose  position  is  indicated  superficially  by  a 
dental  groove  which  indents  the  epithelial  surface  of  the  primitive  gum. 
The  labiodental  strand  divides  at  its  deeper  border  into  a  nearly  vertical 
continuation,  the  labial  lamina,  which  subsequently  becomes  hollow  to 
form  the  labiogingival  groove ;  and  a  horizontal  inwardly  directed  shelf, 
the  dental  lamina,  which  forms  the  earliest  anlage  of  the  enamel,  the 
enamel  organ. 

At  the  beginning  of  the  third  month  the  dental  shelf  shows  upon 
its  deep  margin  a  series  of  shallow  inverted  cups,  one  for  each  of  the 
temporary  teeth,  produced  by  an  up-pushing  of  a  corresponding  series 
of  cone-shaped  areas  of  condensing  mesenchyma  at  the  site  of  each 
tooth  germ.  Each  mesenchymal  thickening  forms  the  anlage  of  a  dental 
papilla.  That  portion  of  the  dental  shelf  which  spreads  out  laterally 
to  cover  the  dental  papilla  of  each  tooth  forms  its  enamel  germ,  from 
which  the  dental  enamel  is  eventually  produced.  Further  development 
of  the  enamel  germ  and  dental  papilla  causes  the  former  to  surround  the 
papilla  like  a  cap.  Figures  311  and  312  show  four  stages  in  the  early 
development  of  a  tooth. 


THF,    TEETH 


331 


During  the  third  month  of  fetal  life  the  anlages  of  all  primitive 
(deciduous,  mill-,  or  temporary}  teeth  are  formed  in  the  above  manner. 
At  about  the  same  time,  also,  a  posterior  growth  upon  the  lingual  side 
of  the  thin  portion  of  the  dental  shelf  which  still  connects  the  enamel 
germs  with  the  oral  epi-  f.  f  f  ._.  .  . 

thelium,  forms  the  anlages  .:•';,';  v /'/.: V-.'"!:^'-'"-X '••  \:  X  : •. . 

of  twenty  of  the  permanent 
teeth.  The  twelve  addi- 
tional permanent  molars 
arise  at  a  later  period  and 
in  a  similar  manner  by  a 
dorsal  extension  of  the 
dental  lamina  which  grows 
backward  through  the  con- 
nective tissue  of  the  alveo- 
lar process  as  a  solid  cell 
column  from  which  the  en- 
amel germs  are  formed 
and  into  which  the  dental 
papilla  grow. 

Further  development 
of  the  dental  anlage  in- 
cludes the  differentiation 
of  the  enamel  germ  011  the 
one  hand  and  of  the  dental 
papilla  on  the  other.  From 
the  former  the  enamel  and 
the  cuticular  epitli  dial 
membrane  arise ;  the  latter 
produces  the  dental  pulp 
and  the  dcntin. 

THE  ENAMEL  GERM. 
— The  enamel  germ  or 

enamel  organ  soon  differentiates  into  three  layers:  (1)  an  inner  enamel 
ej/i/lieUum  which  forms  the  enamel  prisms;  (2)  an  outer  enamel  e/nlln'- 
I  In  in  which  lines  the  dental  sac;  and  (3)  an  intervening  enamel  pulp. 

Tin;  IN x KII  ENAMEL  EPITHELIUM. — The  innermost  cells  of  the 
enamel  organ,  viz.,  those  which  rest  directly  upon  the  dental  papilla, 
soon  become  elongated  and  attain  a  cylindrical  form.  The  nucleus 
moves  toward  the  distal  pole,  and  the  original  basal  end  becomes  modi- 


FIG.  311. — DEVELOPING  TOOTH  FROM  A  HUMAN 
EMBRYO  17  MM.  LONG. 

LF,  dental  groove;  M,  oral  cavity;  OK,  meso- 
blast  of  upper  jaw;  UK,  anlage  of  lower  jaw;  OL, 
epithelium  of  the  primitive  upper  lip,  and  UL, 
of  the  lower  lip;  ZL,  dental  lamina  (labiodental 
strand).  X  120.  (After  C.  Hose.) 


ZL 


LFL rf 


FIG.  312. — DENTAL  ANLAGES  FROM  A  HUMAN  FETUS  40  MM.  LONG. 

Letters  as  in  the  preceding  figure.  LFL,  labial  lamina,  or  anlage  of  the  groove 
between  the  lip  and  the  mandibular  process;  Pp,  dental  papilla;  Z,  outline  of  the 
margin  of  the  tongue;  ZL,  dental  lamina.  X  60.  (After  C.  Rose.) 


FIG.  313. — Two  STAGES  IN  THE  EARLY  DEVELOPMENT  OF  THE  TEETH,  FROM  A  25  MM. 
PIG  EMBRYO. 

In  B  is  seen  the  developing  bone  and  striped  muscle  of  the  lower  jaw.    In  both 
stages  the  dental  papilla  and  the  three  layers  of  the  enamel  organ  are  clearly  shown. 

332 


THE  TEETH  333 

fied  to  take  on  the  characteristics  of  the  distal  end  of  a  columnar  cell. 
A  cuticular  border  appears  upon  the  inner  (originally  basal)  extremities, 
and  as  the  calcareous  substance  of  the  enamel  begins  to  be  deposited  fine 
processes  are  seen  extending  inward  from  the  extremities  of  the  enamel 
cells,  Tomes'  processes.  It  is  around  these  processes  that  the  permanent 


zi 


LV.S 


FIG.  314. — DEVELOPING  TOOTH  FROM  A  HUMAN  FETUS  30  CM.  LONG. 

D,  dentin;  K,  bone  of  the  jaw;  RM,  germinal  layer  of  the  oral  mucosa;  S,  enamel 
organ;  SKZ,  enamel  anlage  of  the  permanent  tooth;  VB,  epithelial  bridge  still  uniting 
the  anlages  of  the  temporary  and  permanent  teeth;  ZL,  disintegrating  dental  lamina; 
SP,  enamel  pulp.  X  30.  (After  C.  Rose.) 

enamel  is  deposited  first  in  the  form  of  globules,  which  become  calcified 
and  meanwhile  fuse  to  form  the  enamel  prisms. 

The  deposit  of  lime  salts  by  the  cylindrical  cells  of  the  inner  enamel 
layer,  ameloblasts  (adamantoblasts) ,  occurs  earliest  at  the  apex  of  the 
dental  germ.  Thus,  it  is  the  enamel  of  the  face  of  the  tooth  crown  which 
is  first  formed,  and  this  is  therefore  its  thickest  portion.  The  enamel 
on  the  sides  of  the  tooth  crown  appears  later  and  hence  it  gradually 


334 


THE  DIGESTIVE  SYSTEM 


tapers  in  thickness  as  it  approaches  the  neck  of  the  tooth,  in  which  latter 
place  the  last  formed  enamel  is  found. 


FIG.  315. — A  DEVELOPING  TOOTH  FROM  AN  INFANT'S  JAW. 
a,  papilla;  b,  crown;  c,  outer  enamel  epithelium.    Hematein  and  eosin.    Photo.    X  65. 

The  nucleated  bases  (originally  apices)  of  the  cylindrical  cells  of  the 
inner  enamel  epithelium  are  also  marked  by  a  sharp  cuticular  margin 
and  rest  upon  the  adjacent  cells  of  the  enamel  pulp,  the  innermost  cells 


THE  TEETH 


335 


of  which  retain  a  characteristic  epithelial  appearance.  The  thin  layer 
formed  by  the  uncalcified  bases  of  the  adamantoblasts,  which  still  cover 
the  free  surface  of  the  enamel  at  the  eruption  of  the  tooth,  remains  as 
the  highly  cornified  dental  cuticular  membrane  (of  Nasmyth).  This  is 
soon  lost  over  the  crown  by 
reason  of  mechanical  wear. 

THE  OUTER  ENAMEL  EPI- 
THELIUM.— T  h  e  outermost 
cells  of  the  enamel  germ  are 
immediately  in  contact  with 
the  mesenchyma  of  the  prim- 
itive jaw.  This  connective  tis- 
sue forms.,  toward  the  end  of 
the  third  month,  a  vascular  in- 
vesting sheath  or  dental  sac, 
which  incloses  the  entire  den- 
tal germ  and  finally,  by  grad- 
ually encroaching  upon  the 
narrow  neck  which  still  con- 
nects the  enamel  germ  with  the 
dental  lamina,  severs  the  con- 
nection of  these  organs  so  that 
the  primitive  tooth  lies  free 
within  the  dental  sac.  The 
outer  enamel  epithelium,  which 
lines  all  portions  of  the  dental 
sac  except  at  the  base  of  the 
dental  papilla,  forms  several 


:__ -  -''-  •  \  J 


FIG.  316.— A  PORTION  OF  FIG.  315,  NEAR  THE 
APEX  OF  THE  DEVELOPING  TOOTH. 


a,  enamel  epithelium;  6,  ameloblasts;  c, 
enamel;  d,  dentin;  e,  odontoblasts;  /,  border 
of  the  dental  pulp.  Between  the  formed 
enamel  and  the  ameloblasts  Tomes'  processes 
can  be  seen.  Hematein  and  eosin.  X  550. 


layers    of    flattened   epithelial 
cells.     Eemnants  of  this  cell 
layer  frequently  persist,  in  re- 
lation to  the  inner  margin  of  the  bony  alveolus  whose  wall  is  produced 
by  intramembranous  ossification  in  the  connective  tissue  surrounding  the 
embryonic  dental  sac. 

THE  ENAMEL  PULP. — This  structure  is  produced  by  a  remarkable 
differentiation  which  occurs  within  the  mid-portion  of  the  enamel  organ. 
The  epithelial  cells  of  this  region,  which  at  first  appear  to  form  a 
delicate  syncytium,  become  separated  by  wider  and  wider  intercellular 
spaces,  and  are  thus  drawn  out  into  stellate  forms  with  long  anastomosing 
processes.  The  resulting  cells  closely  resemble  in  form  the  connective 


336 


THE  DIGESTIVE  SYSTEM 


tissue  cells  of  embryonal  or  gelatinous  connective  tissue.  They  are,  how- 
ever, inclosed  on  all  sides  by  the  epithelial  cells  of  the  inner  and  outer 
enamel  epithelium  and,  like  other  epithelial  tissues,  are  never  penetrated 
by  blood-vessels. 

The  enamel  pulp  appears  to  serve  a  purely  mechanical  function,  it 
being  a  soft  tissue  through  which  the  grow- 
ing tooth  readily  pushes  its  way  to  the  sur- 
d      face. 

The  Dental  Papilla.— The    dental    pa- 
dc     pilla  is  a  mesenchymal  structure  which  is  in- 
vested by  and  grows  into  the  enamel  organ. 
Coincident  with  the  appearance  of  the  ainelo- 
T'p'  blasts  in  the  enamel  organ,  the  superficial 
cells  of  the  dental  papilla  become  enlarged, 
elongated,  and  so  arranged  as  to  form  a  con- 
0       tinuous  layer  of  odontoblasts  on  the  surface 
of  the  papilla.    These  cells  apparently  secrete 
a  thin  homogeneous  layer,  membrana  prc- 
formativa    (Raschkow),   which   serves   as   a 
basement  membrane  upon  which  the  amelo- 
blasts   deposit   the   enamel  prisms;   it   also 
forms  the  anlage  of  the  granular  layer  of 
Tomes. 

The  odontoblasts  now  form  the  DENTIST 
in  a  manner  entirely  analogous  to  the  de- 
posit of  bone  by  the  osteoblasts,  processes  of 
the  odontoblasts  being  included  within  the 
deposit  of  den  tin  to  form  the  dentinal  fibers. 

Irregular  spaces,  occurring  in  the  dentin  and  granular  layer,  in  which 
no  calcification  occurs  produce  the  inter  globular  spaces. 

The  central  mass  of  the  dental  papilla  develops  the  rcticular  tissue 
of  the  dental  pulp.  The  blood-vessels  and  nerves  enter  the  pulp  through 
the  base  of  the  papilla,  which  thus  becomes  the  anlage  of  the  root  canal. 
The  CEMENTUM  is  formed  by  intramembranous  ossification  occurring 
in  that  portion  of  the  dental  sac  which  invests  the  base  of  the  dental 
papilla  and  the  primitive  root  of  the  tooth. 

The  process  of  cementogenesis  is  essentially  similar  to  that  of  peri- 
chondrial  ossification.  The  vascular  mesenchyma  of  the  dental  sac 
breaks  through  the  epithelial  sheath  (the  root  extension  of  the  enamel 
organ),  and  through  the  agency  of  modified  mesenchymal  cells  similar 


FIG.  317. — ODONTOBLASTS 
AND  DENTIN  OP  THE 
TOOTH  OF  A  NEW-BORN 
CAT. 

o.odontoblasts;  Tp,  Tomes' 
fibrils,  prolongations  of  the 
odontoblasts;  dc,  dentinal 
canal  in  the  dentin  (d). 
X  500.  (After  Prenant, 
Bouin  and  Maillard.) 


THE  TONGUE  337 

to  the  osteoblasts,  the  cementoblasts,  deposits  cementum  upon  the  dentin 
of  the  root.  The  first  deposit  is  made  in  the  neck  region,  and  the 
deposition  progresses  from  thence  to  the  apex  of  the  root,  where  the 
thickest  layer  is  subsequently  found.  Cementoblasts  become  enclosed 
in  lacunae  of  the  cementum  and  persist  as  cementum  cells.  The  periph- 
eral layer  of  the  root  portion  of  the  sac  differentiates  into  a  dense  fibro- 
elastic  lamina  which  serves  both  as  a  pericementum  to  the  tooth,  and  as 
periosteum  to  the  bone  of  the  jaw.  The  pericementum  includes  besides 
cementoblasts  also  odontodasts  which  become  active  as  tooth  destroyers 
at  about  the  age  of  five  years.  They  absorb  the  roots  of  the  deciduoias 
teeth,  and  thus  open  the  way  for  the  eruption  of  the  permanent  teeth. 


THE  TONGUE 

The  tongue  consists  essentially  of  a  mass  of  voluntary  muscle  in- 
vested by  a  continuation  of  the  mucous  membrane  of  the  mouth  and 
pharynx.  The  fibers  of  this  striated  muscle  are  separated  into  two  lateral 
halves  by  a  median  septum  of  dense  connective  tissue  which  extends 
from  the  base  to  the  tip  of  the  organ,  and  is  known  as  the  lingual 
septum. 

The  Muscle  Fibers.— The  muscle  fibers  include  two  groups:  (1) 
the  intrinsic,  those  of  the  lingualis  or  tongue  muscle  proper;  (2)  the 
extrinsic,  those  entering  from  without  and  serving  to  attach  the  tongue : 
the  geuioglossus,  the  hyoglossus,  the  styloglossus,  the  palatoglossus,  and 
the  chondroglossus.  The  fibers  are  disposed  in  three  planes  and  are  so 
arranged  that  the  bundles  cross  one  another  at  right  angles.  They  thus 
form:  (1)  sagittal  or  vertical  fiber  bundles  which  are  slightly  inclined 
outward  from  the  septum  linguae  and  are  derived  from  the  liugualis 
muscle,  supplemented  in  the  inferior  median  portion  by  fibers  from 
the  genioglossus  and  the  hyoglossus;  (2)  longitudinal  fibers  peripherally 
distributed  and  running  from  the  base  to  the  apex  of  the  tongue,  de- 
rived chiefly  from  the  lingualis  but  supplemented  on  the  under  surface 
by  the  styloglossus,  and  chondroglossus;  (3)  transverse  or  horizontal 
fibers  extending  laterally  from  the  septum  linguae,  which  are  also  de- 
rived from  the  lingualis  muscle,  and  include  a  few  fibers  from  the 
palatoglossus. 

The  interlacing  bundles  of  muscle  fibers  are  embedded  in  loose 
areolar  and  adipose  tissue.  The  muscle  fibers  are  inserted  into  the 
corium  of  the  lingual  mucous  membrane,  their  sarcolernma  being  firmly 


338 


THE  DIGESTIVE  SYSTEM 


adherent  to  the  connective  tissue  of  the  mucosa,  which  invests  the 
rounded  blunt  extremity  of  the  muscle  cell.  Many  of  these  muscle 
fibers  are  branched. 

The  Mucous  Membrane. — The  mucous  membrane  of  the   tongue 


FIG.  318. — VIEW  OF  DORSUM  OF  TONGUE,  SHOWING  THE  VARIOUS  PAPILLA,  THE 
TONSILS  AND  THE  FAUCES. 

1,  circumvallate  papillae;  2,  foramen  cecum;  3,  fungiform  papillae;  4,  filiform 
papillae;  5,  transverse  and  oblique  rugae;  6,  mucous  glands;  7,  tonsils;  8,  tip]  of 
epiglottis;  9,  median  glosso-epiglottidean  fold;  /,  foliate  papillae;  L,  lenticular  papil- 
lae. (After  Sappey.) 

consists  of  a  thick  corium,  and  an  epithelial  covering.  The  deeper 
part  of  the  CORIUM,  consisting  of  loose  areolar  tissue,  is  intimately 
connected  with  the  muscle.  The  superficial  portion  of  the  corium, 
containing  denser  areolar  tissue,  carries  upon  its  surface  dorsally  con- 
nective tissue  papillce  of  unusually  large  size  which  project  into  the 


THE  TONGUE 


339 


epithelial  coat.    The  surface  of  the  larger  of  these  papillae  is  not  smooth, 
but  is  covered  with  small  secondary  papillae. 

The  dorsal  surface  of  the  tongue  presents  a  sharp  structural  differ- 
ence between  its  anterior  and  posterior  portions.  The  papillae  are 
limited  to  the  anterior  portion,  which  includes  about  two-thirds  of 
the  entire  surface;  this  is  known  as  the  papillary  area.  The  posterior 


FIG.  319. — ONE  LATERAL  HALF  OF  A  CORONAL  SECTION  OF  A  DOG'S  TONGUE. 

The  dorsal  surface  presents  numerous  large  filiform  papillae,  a,  lingual  papilla; ; 
6,  corium;  c,  the  fibromuscular  substance  of  the  tongue.  Hematein  and  eosin. 
Photo.  X  6. 

one-third  lacks  papillae,  and  is  of  lymphoid  character,  hence  known  as 
the  lymphoid  area  (lingual  tonsil).  These  two  areas  represent  the 
originally  separate  anlages  from  which  the  definitive  tongue  develops: 
the  anterior  unpaired  tuberculum  impar,  and  the  posterior  paired  radix 
lingua.  The  line  of  fusion  is  indicated  in  the  fetus  and  infant  by  a 
shallow  V-shaped  groove,  the  sulcus  terminalis.  This  subsequently 
disappears,  and  the  boundary  then  remains  marked  by  the  position  of  the 
circum  vail  ate  papilla?.  The  papillary  area  constitutes  the  tongue  proper. 
EPITHELIUM. — The  epithelium  of  the  tongue  is  of  the  stratified 


340 


THE  DIGESTIVE  SYSTEM 


squamous  variety.  Upon  the  under  surface  and  margins  of  the  organ 
its  surface  is  smooth,  but  on  the  dorsum  of  the  tongue  the  stratified 
epithelium  forms  tall  projections,  which  correspond  with  the  papilla? 
of  the  corium,  and  which  constitute  the  so-called  lingual  papillae.  These 
papilla?  are  of  three  varieties:  (1)  conical  or  filiform;  (2)  fungiform; 
and  (3)  circumvallate. 

The  Conical  or  Filiform  Papilla. — These  papilla?  consist  of  flattened 


FIG.  320.— FILIFORM 


ILL*:  OP  THE  DOG'S  TONGUE. 


a,  papillae;  b,  corium;  c,  insertion  of  the  muscular  fibers  into  the  border  of  the  corium. 
Hematein  and  eosin.     Photo.     X  60. 


and  elongated  epithelial  cells  which  are  often  so  arranged  as  to  produce 
a  slender  conical  projection  or  epithelial  tuft  of  variable  height,  which 
covers  the  apex  of  each  connective  tissue  papilla.  This  type  is  the 
most  abundant  of  the  three  varieties  of  lingual  papilla?.  They  are 
found  upon  all  portions  of  the  dorsum  of  the  tongue.  They  range  in 
height  from  0.5  to  2.5  millimeters. 

The  Fungiform  Papilla. — The  fungiform  papilla?  are  formed  by  a 
large  connective  tissue  papilla  or  core  which  projects  above  the  general 
level  of  the  epithelial  surface  and  is  covered  by  a  smooth  layer  of  strati- 
fied squamous  epithelium  in  which  occasional  taste  buds  are  found.  This 


THE  TONGUE 


341 


variety,  though  much  less  abundant  than  the  former,  is  still  very 
numerous  and  may  be  found  upon  any  or  all  portions  of  the  dorsum 
of  the  tongue,  where  they  are  irregularly  scattered  among  the  filiform 
papillae.  The  fungiform  variety  are  most  abundant  near  the  margin 
of  the  tongue  on  its  dorsal  surface.  Their  maximum  height  is  about 
1.5  millimeters. 

Tli  e .  CircumvaUate  .  Papillae. — The  circumvallate  papilla?  form  a 
group  of  from  eight  to  twelve 
elevations  which  are  situated 
at  the  base  of  the  tongue,  and 
are  arranged  in  the  form  of  a 
V,  the  apex  being  directed 
toward  the  larynx.  These 
papilla?  are  much  broader  (2 
to  3  millimeters)  than  either 
of  the  former  varieties.  They 
extend  slightly  above  the  gen- 
eral level  of  the  epithelial  sur- 
face, are  of  an  inverted  coni- 
cal shape,  and  are  covered  by 
a  smooth  layer  of  stratified 
'squamous  epithelium.  Their 
base  is  surrounded  by  a  deep 
circular  excavation,  lined  by 
an  invagination  of  the  layer 
of  stratified  epithelium, 
which  thus  forms  a  deep 
trench  about  the  base  of  the 
papilla. 

The  epithelium  which 
covers  the  sides  of  the  cir- 
cumvallate papillae,  as  well  as  that  forming  the  lateral  wall  of  the  trench 
contains  large  numbers  of  TASTE  BUDS  (see  Chap.  VI).  The  large  cen- 
tral connective  tissue  papilla  carries  upon  its  surface  many  small  sec- 
ondary papillae  of  the  corium,  which  project  into  the  epithelial  coat  of  the 
circumvallate  papilla  upon  its  free  surface,  but  are  not  found  upon  its 
lateral  margins. 

On  the  lateral  margins  of  the  tongue,  just  in  front  of  the  anterior 
pillars  of  the  fauces,  occur  a  variable  number  of  transverse  parallel 
folds  or  leaves,  the  foliate  papillae.  These  are  only  slightly  developed 


FIG.  321. — A  FILIFORM  AND  A  FUNGIFORM 
PAPILLA,  FROM  AN  INJECTED  SPECIMEN  OF 
TONGUE  OF  CAT. 


342 


THE  DIGESTIVE  SYSTEM 


in  man,  but  are  well  developed  in  the  rabbit  and  certain  other  rodents. 
They  contain  numerous  taste  buds.  In  the  lymphoid  area  also,  at  the 
anterior  lateral  margins,  are  a  group  of  low  irregularly  disposed  mucous 
folds,  the  so-called  lenticular  papillce. 


FlG.   322. — ClRCUMVALLATE  PAPILLA  OF  HUMAN  TONGUE.    X55. 


Mucous  and  SEROUS  GLANDS  occur  in  the  deeper  portion  of  the 
corium  of  the  tongue  and  among  its  muscle  bundles;  they  open  upon 
its  epithelial  surface  between  the  papillae.  These  glands  are  most 
abundant  at  the  base  of  the  organ  but  are  also  found  along  its  margins 
as  far  forward  as  the  tip,  where  a  pair  of  small  tubulo-acinar  sero- 
mucous  glands  lie  on  either  side  of  the  median  septum  and  open  upon 
the  ventral  surface  of  the  tongue.  These  are  the  anterior  lingual 


THE  TONGUE 


343 


glands  of  N"uhn.  The  serous  glands  of  von  Ebner  are  confined  to  the 
region  of  the  circumvallate  papillae  at  the  base  of  the  tongue.  They 
pour  their  secretion  into  the  trench  which  surrounds  the  base  of  the 
papilla  or  -into  the  crypts  of  the  lingual  tonsil.  Other  lingual  glands, 
of  the  small  tubulo-acinar  mucous  type,  occur  at  various  portions  of 
the  dorsal  surface  of  the  tongue,  being  especially  abundant  in  the 
lymphoid  area. 

The  Lingual  Tonsil. — The  lingual  tonsil  (Fig.  249)  is  a  con- 
siderable collection  of  lym- 
phoid nodules  which  is 
found  at  the  base  of  the 
tongue  in  and  about  the 
median  line.  These  nod- 
ules are  grouped  about  a 
large  funnel-shaped  crypt, 
the  foramen  cecum,  which 
opens  at  the  apex  of  the  V 
formed  by  the  group  of 
circumvallate  papillae  and 
which  in  the  embryo  forms 
the  lingual  extremity  of 
the  so-called  duct  of  the 
thyroid  gland  (iliyroglos- 
sal  duct).  Several  smaller 
crypts  are  also  included  in  the  region  of  the  lingual  tonsil. 

The  lymphoid  nodules  are  embedded  in  the  mucosa  or  corium  of  the 
tongue  and  are  surrounded  by  mucous  glands,  many  of  whose  ducts 
penetrate  between  the  nodules  to  open  into  the  branching  crypts. 
Lymphocytes,  apparently  derived  from  the  nodules,  infiltrate  the  sur- 
rounding connective  tissue  and  epithelium  and  find  their  way  into  the 
lumen  of  the  tonsillar  crypts. 

The  Blood-vessels  of  the  Tongue.— The  blood-vessels  of  the  tongue 
are  supplied  by  large  arteries  (branches  of  the  lingual  artery)  which, 
with  the  corresponding  veins,  are  embedded  in  the  muscular  portion  of 
the  organ  and  supply  capillary  vessels  to  this  tissue.  From  these  ar- 
teries, also,  small  arterial  branches  enter  the  deeper  portion  of  the 
corium  and  form  a  capillary  plexus  which  supplies  the  connective  tissue 
and  whose  terminal  ramifications  extend  to  the  very  apex  of  the  con- 
nective tissue  papilla?.  The  blood  is  returned  by  veins  which  pursue 
a  similar  course. 


FIG.  323.— Two  FOLIATE  PAPILLE  FROM  A  RAB- 
BIT'S TONGUE,  SHOWING  NUMEROUS  TASTE  BUDS 
ALONG  THEIR  LATERAL  MARGINS. 


344  THE  DIGESTIVE  SYSTEM 

The  Lymphatics. — The  lymphatics  form  a  superficial  set  of  small 
vessels  and  tissue  spaces  beneath  the  epithelial  layer,  which  are  espe- 
cially abundant  in  the  region  of  the  lingual  tonsil  at  the  base  of  the 
tongue.  The  lymphatic  vessels  of  this  superficial  plexus  frequently 
encircle  the  lymphoid  nodules.  A  deeper  plexus  of  lymphatics  in  the 
loose  connective  tissue  of  the  submucosa  receives  the  lymph  from  the 
superficial  plexus  and  conveys  it  by  efferent  lymphatic  vessels  to  the 
deep  cervical  lymphatic  glands. 

The  Nerve  Supply. — The  nerve  supply  of  the  tongue  comprises 
cerebral,  both  sensory  and  motor  fibers,  and  sympathetic  fibers.  The 
sympathetic  elements  supply  the  glands  and  blood-vessels;  small  ganglia 
occur  along  their  course.  The  motor  fibers  supplying  the  striped  muscle 
are  derived  from  the  hypoglossal  nerve.  These  end  in  motor  end- 
piates.  The  sensory  fibers  arise  from  the  lingual  branch  of  the  tri- 
geminal  and  the  glossopharyngeal  nerves.  These  mediate  both  general 
sensibility  and  the  sensation  of  taste.  The  fibers  which  receive  the 
stimuli  of  general  sensibility  end  as  naked  varicose  fibrils  in  the  con- 
nective tissue  of  the  body  of  the  tongue,  and  in  the  submucosa  of 
the  papilla?.  They  are  accompanied  by  small  ganglia.  Certain  fibers 
also  end  in  muscle  spindles.  The  fibers  of  special  gustatory  sensation 
are  also  distributed  to  the  papilla?;  the  chorda  tympani  (branch  of 
the  facial)  component  of  the  lingual  branch  of  the  trigeminal  supplying 
the  anterior  two-thirds,  the  glossopharyngeal  the  posterior  one-third  of 
the  tongue.  At  the  base  of  the  tongue  small  nerve  bundles  of  taste 
fibers  are  distributed  to  the  circumvallate  papilla,  and  form  a  subepi- 
thelial  plexus  from  which  fibrils  are  distributed:  (1)  to  the  interior 
of  the  taste  buds  where  they  end  in  relation  with  the  gustatory  cells, 
intragemmal  fibers;  (2)  to  the  surface  of  the  taste  buds,  perigemmal 
fibers;  and  (3)  to  the  intervening  portions  of  the  epithelial  layer,  where 
they  end  between  the  epithelial  cells  as  in  other  parts  of  the  tongue, 
intergemmal  fibers  (Fig.  175,  page  101).  The  taste  buds  of  the  soft 
palate  are  innervated  through  the  palatine  nerves  (great  superficial 
petrosal  component)  of  the  trigeminal. 


THE  ALIMENTARY  CANAL 

GENERAL  CHARACTERISTICS  OF  THE  WALLS 

It  is  convenient  to  consider  collectively  under  this  head  the  pharynx, 
esophagus,   stomach,  and  the  small  and  large  intestines.     This  tract 


THE  ALIMENTARY  CANAL 


345 


forms  a  continuous  tube  whose  wall  has,  throughout  its  entire  extent, 
many  common  characteristics.    Thus  the  wall  in  all  portions  consists  oJ 


Tongue 


Parotid  gland 
Sublingual  gland 
Submaxillary  gland 


Pylorus 


Appendices  epiploicae 

Jejunum 

Longt.  muscle  band 


Cecum 
Vermiform  appendi. 


FIG.  324. — DIAGRAM  OF  THE  ALIMENTARY  CANAL  OF  MAN. 

7s,  small  intestine;  Ca,  Ct,  and  Cd,  ascending,  transverse  and  descending  portions 
of  the  colon;  Ph,  pharynx;  Vic,  ileocolic  valve.  (Adapted  from  Wiedersheim.) 

.four  coats  which  are  respectively  known,  from  within  outward,  as  the 
mucous,  suhmucous,  muscular,  and  fibroserous.  The  three  outermost 
coats  are  of  very  similar  structure  in  all  portions  of  the  tract. 

The    Fibroserous    Coat. — In  the  abdominal  cavity  the  outermost 


346 


THE  DIGESTIVE  SYSTEM 


coat  is  derived  from  the  peritoneum,  by  which  the  stomach  and  intestines 
are  invested.  In  the  upper  portion  of  the  tract,  pharynx  and  esophagus, 
the  serous  coat  is  replaced  by  a  layer  of  areolar  connective  tissue  which 
usually  contains  much  fat.  In  the  abdomen  the  homologous  subserous 
connective  tissue  is  covered  by  a  layer  of  mesothelium.  The  connective 
tissue  of  the  outer  fibroserous  coat  contains  the  larger  blood  and  lym- 
phatic vessels  whose  branches  are  distributed  to  the  three  inner  coats. 
The  Muscular  Coat.  —  The  muscular  coat,  situated  next  within  the 
fibroserous,  is  divisible  into  two  layers,  an  outer  longitudinal  the  direc- 

tion of  whose  fibers  is  parallel 
to  the  long  axis  of  the  canal, 
and  an-  inner  transverse  layer 
whose  fibers  are  circularly  dis- 
posed. The  two  layers  are 
united  by  a  thin  septum  of 
areolar  connective  tissue  which 
serves  for  the  support  of  the 
larger  blood-vessels  and  lym- 
phatics, whose  capillaries  are 
distributed  to  the  muscular 
coat.  This  septum  also  con- 
tains a  coarse-meshed  nerve 
plexus,  consisting  of  small  an- 
astomosing nerve  trunks  which 
are  composed  in  large  part  of 

non-medullated  fibers,  at  whose  intersections  are  numerous  small  sym- 
pathetic ganglia,  the  myenteric  (Auerbach's)  plexus  and  ganglion. 

Below  the  level  of  the  junction  of  the  middle  and  lower  third  of  the 
esophagus,  and  including  the  musculature  of  the  stomach  and  intestines, 
the  muscle  is  entirely  of  the  non-striated  or  smooth  variety.  In  the 
pharynx  and  upper  third  of  the  esophagus,  the  striated  or  voluntary 
type  of  muscle  is  exclusively  found.  In  the  mid-portion  of  the  esophagus 
both  striated  and  non-striated  muscle  occur  in  varying  proportions,  oc- 
casional striated  fibers  being  found  even  in  the  lower  third  of  the 
organ. 

The  Submucous  Coat.  —  The  submucous  coat  consists  of  loose 
areolar  tissue,  and  serves  for  the  support  of  the  larger  blood  and 
lymphatic  vessels  which  supply  this  coat  and  the  mucosa.  A  second 
plexus  of  nerve  fibers,  similar  in  structure  to  the  intramuscular  plexus, 
is  found  in  the  deeper  layers  of  the  submucosa,  and  is  known  as  the 


FIG.  325. — SURFACE  VIEW  OF  AUERBACH'S 
INTRAMUSCULAR  NERVE  PLEXUS,  FROM  THE 
ESOPHAGUS  OF  A  CAT. 

Methylene  blue.  X  40  to  50.  (After  DeWitt.) 


THE  ALIMENTAKY  CANAL  347 

submucous  (Meissner's)  plexus.  Its  nerve  trunks  and  ganglia  are  some- 
what smaller  than  those  of  the  myenteric  plexus.  The  submucous 
plexus  supplies  the  muscular  and  glandular  tissues  of  the  mucous  mem- 
brane. 

The  Mucous  Membrane. — The  mucous  coat  or  mucosa  of  the 
gastro-intestinal  canal  contains  four  typical  structures,  (1)  an  internal 
lining  epithelium;  (2)  the  muscularis  mucosas  which  forms  the  outer- 
most layer;  between  these  is  (3)  a  tunica  propria  or  corium  of  diffuse 
lymphoid  or  areolar  tissue,  which  serves  chiefly  for  the  support  of  (4) 
the  secreting  glands. 

The  muscularis  mucosce  usually  consists  of  a  double  layer  of  smooth 
muscle,  the  outer  being  longitudinally,  the  inner  circularly  disposed. 
This  layer  is  most  highly  developed  in  the  esophagus. 

The  tunica  propria  consists  of  delicate  fibre-elastic  and  reticular 
tissue  whose  volume  is  in  inverse  proportion  to  that  of  the  secreting 
glands.  It  is  most  abundant  in  the  esophagus.  In  the  stomach  and 
intestines  it  is  considerably  infiltrated  by  lymphocytes  and  often  con- 
tains diffuse  lymphoid  tissue.  Small  lymph  nodules  are  also  found 
in  the  deeper  part  of  this  membrane;  they  progressively  increase  in 
size  toward  the  lower  portion  of  the  tract,  where  they  form  the  solitary 
nodules  of  the  intestine. 

.  The  nature  of  the  lining  epithelium  and  the  type  of  glands  differs 
in  each  succeeding  portion  of  the  canal,  and  must,  therefore,  together 
with  the  other  peculiarities  of  the  several  subdivisions  of  the  tract, 
be  separately  considered. 

THE  PHARYNX 

The  pharynx  may  be  subdivided,  upon  histological  as  well  as  physio- 
logical grounds,  into  (1)  an  upper  respiratory  portion,  or  nasopharynx, 
and  (2)  a  lower  portion,  oropharynx  and  laryngopharynx ;  only  the 
latter  of  these  properly  belongs  to  the  alimentary  tract.  The  soft  palate 
and  uvula  form  a  thin  partition  between  the  naso-  and  oropharynx.  The 
nasopharynx  has  already  been  described  as  a  part  of  the  respiratory 
system  (see  Chapter  XII). 

The  mucous  membrane  of  the  lower  portion  of  the  pharynx  is  lined 
by  stratified  squamous,  epithelium  which  rests  upon  a  thick  corium  of 
areolar  tissue.  The  tunica  propria  is  well  supplied  with  thin-walled 
blood-vessels  and  lymphatics,  and  contains  many  mucus-secreting  glands 
of  the  tubulo-acinar  type  whose  secreting  portions  lie  deeply  embedded 
in  the  connective  tissue  of  the  muscular  coat. 


348  THE  DIGESTIVE  SYSTEM 

There  is  no  muscularis  mucosas  in  the  mucous  membrane  of  the 
pharynx;  its  place  is  taken  by  a  layer  of  connective  tissue  which  is 
exceedingly  rich  in  longitudinal  elastic  fibers.  This  layer  lies  imme- 
diately upon  the  muscular  coat,  into  which  processes  of  fibro-elastic  tissue 
extend  between  the  muscular  bundles;  hence  this  fibro-elastic  layer  also 
serves  as  a  submucosa. 

The  superficial  layer  of  the  corium  contains  diffuse  collections  of 
lymphoid  tissue  and  occasional  small  lymph  nodules. 

The  muscular  coat  of  the  pharynx  is  formed  by  its  constrictor 
muscles.  Their  striated  fibers  mostly  pursue  an  oblique  course.  Where 
these  muscles  are  not  immediately  attached  to  the  periosteum  of  the 
vertebrae,  the  pharynx  is  invested  with  an  outer  coat  of  areolar  con- 
nective tissue  by  which  it  is  loosely  united  to  adjacent  organs. 

ESOPHAGUS 

The  esophagus  or  gullet  is  a  short  tube  about  25  centimeters  (10 
inches)  in  length,  connecting  the  pharynx  with  the  cardia  of  the 
stomach.  Its  wall  contains  the  usual  four  coats:  (1)  the  outer  fibrous; 
(2)  muscular;  (3)  submucous;  and  (4)  mucous  (fig.  327). 

The  Outer  Fibrous  Coat. — The  outer  fibrous  coat  envelops  the 
wall  of  the  esophagus  and  unites  it  to  the  adjacent  organs.  It  consists 
of  loose  fibrous  tissue,  and  contains  the  blood  and  lymphatic  vessels 
and  nerve  trunks  which  supply  the  three  inner  coats.  It  is  not  in- 
vested by  a  serous  layer. 

The  Muscular  Goat. — The  muscular  coat  contains  an  outer  longi- 
tudinal and  an  inner  circular  layer  of  muscle  fibers,  which  are  sep- 
arated by  a  narrow  septum  of  loose  fibrous  tissue.  In  the  upper  third 
of  the  esophagus  the  muscle  is  of  the  striated  variety,  in  the  middle 
third  it  is  mixed,  in  the  lower  third  it  is  generally  smooth.  The  distri- 
bution of  the  muscle  in  the  lower  third  is  subject  to  great  individual 
variation,  and  occasionally  striated  fibers  are  often  found  all  the  way 
down  to  the  diaphragmatic  opening. 

The  fibrous  septum  between  the  muscular  layers  contains  the  larger 
blood-vessels  and  the  myenteric  nerve  plexus. 

The  Submucous  Coat. — The  submucous  coat  forms  a  layer  of 
areolar  connective  tissue  which  firmly  unites  the  muscular  and  the 
mucous  coats.  It  contains  those  blood  and  lymphatic  vessels,  together 
with  the  submucous  nerve  plexus,  whose  branches  supply  the  mucous 
membrane.  It  also  contains  a  considerable  number  of  tubulo-acinar 


THE  ALIMENTARY  CANAL 


349 


mucous  glands  whose  ducts  enter  the  mucous  membrane  and  open  upon 
the  free  epithelial  surface.  The  secreting  acini  of  these  glands  are 
short  branching  tubules  with  ampullary  dilatations;  they  possess  a 
characteristic,  tortuous  form.  Their  columnar  secreting  cells  have  a 
strong  affinity  for  muchematein  and  other  mucous  stains.  This  basophil 


FIG.  326. — LONGITUDINAL,  SECTION  THROUGH  REGION  OP  TRANSITION  FROM  ESOPHA- 
GUS (RIGHT)  TO  CARDIAC  END  OP  STOMACH  (LEFT).  X22. 


reaction,  together  with  the  situation  of  their  isolated  groups  of  secreting 
acini  in  tlie  submucosa,  sharply  distinguishes  the  esophageal  mucous 
glands  from  the  glands  of  the  stomach  and  intestine,  except  those  of  the 
duodenum. 

The  number  of  the  esophageal  glands  in  man  is  extremely  variable. 
This  numerical  variability  is  associated  with  frequent  cyst  formation, 
stasis  of  secretion,  and  atrophy  of  the  glandular  elements;  conditions 
indicating  small  functional  significance.  In  certain  mammals,  e.g., 
rodents,  ox,  horse,  sheep,  cat,  and  bat,  glands  are  entirely  lacking; 


350 


THE   DIGESTIVE   SYSTEM 


in  others,  e.g.,  opossum,  dog,  pig,  they  are  very  abundant.  Except  in 
man,  the  mucous  alveoli  contain  demilunes.  Esophageal  glands  are  the 
exception  rather  than  the  rule  in  mammals.  The  fact  that  they  are  ab- 
sent in  all  vegetable  feeders  but  present  in  mixed  feeders  indicates  that 
they  have  a  chemical  rather  than  a  mechanical  function  (Goetsch,  Amer. 

Jour.  Anat.,  10,  1,1910). 
The  Mucous  Coat 
(Mucosa). — The  mucous 
coat  of  the  esophagus 
consists  of  a  tunica  pro- 

•    . ,.•»- — -ii  ^is.*       a*  pria  or  corium  of  areolar 

tissue  which  rests  upon  a 
-c.  M. well-developed  muscularis 
mucosffi  and  is  covered  on 
its  free  surface  by  strati- 
fied squamous  epithelium. 
The  muscularis  mu- 
cosa3  contains  consider- 
able bundles  of  smooth 
muscles  whose  general  di- 
rection is  a  longitudinal 
one  in  its  outer,  and  cir- 
cular in  its  inner  portion. 
This  la}*er  forms  the 
outermost  stratum  of  the 
mucous  coat,  and  is  pene- 
trated by  the  ducts  of  the 
deep  mucous  glands 
whose  secreting  acini  lie 
in  the  submucosa. 

The  inner  portion  of 
the   tunica    propria    car- 


FIG.  327. — TRANSVERSE  SECTION  OF  HUMAN 
ESOPHAGUS  THROUGH  LOWER  THIRD. 

Z,,  lumen;  F.,  fibrous  tunic;  C.  A/.,  circular  muscle 
layer;  L.  M.,  longitudinal  muscle  layer;  G.,  mucous 
glands  in 'submucosa  (S.)}  L.N.,  lymph  nodule; 
M.  M.,  muscularis  mucosse;  T.  P.,  tunica  propria; 
E.,  stratified  squamous  epithelium;  B.  V.,  blood 
vessels.  (Adapted  from  Merkel.) 


ries  on  its  surface  many  tall  connective  tissue  papillae  which  project  well 
into  the  epithelial  coat  and  which  closely  resemble  the  vascular  papillae 
of  the  skin. 

The  mid-portion  of  the  corium  is  penetrated  by  the  excretory  ducts  of 
the  mucous  glands.  These  are  at  first  lined  by  low  columnar  cells  which, 
as  they  approach  the  epithelial  surface,  are  changed  into  several  layers  of 
flattened  cells,  which  thus  form  a  thin  stratified  lining,  continuous  with 
the  superficial  stratified  squamous  epithelium  of  the  esophageal  mucosa. 


THE    ALIMENTARY    CANAL 


351 


Many  of  these  ducts  possess  small  cystic  dilatations  which  are  found  in 
the  connective  tissue  of  the  corium  or  occasionally  in  the  submucosa. 

SUPERFICIAL  GLANDS. — At  about  the  level  of  the  cricoid  cartilage 
the  esophageal  mucous  membrane  presents 
two  lozenge-shaped  depressions,  one  on 
either  side,  whose  diameter  varies  from  1 
centimeter  down  to  microscopical  size. 
These  areas  mark  the  site  of  the  superficial 
glands  of  the  esophagus  (Hewlett)  or  up- 
per cardiac  glands  (Schafer).  These  are 
short  branched  tubular  glands  which 
closely  resemble  those  of  the  cardiac  re- 
gion of  the  stomach.  They  are  con- 
fined to  the  mucous  membrane;  their 
tubules,  in  marked  contrast  to  those  of 
the  deep  mucous  glands  of  the  esoph- 
agus, never  penetrating  the  muscularis 
mucosa?,  which,  however,  is  considerably 
thinned  beneath  the  superficial  glands 
These  glands  secrete  a  mucinous  fluid, 
but  their  cells  are  not  so  strongly  ba- 
sophilic  as  those  of  true  mucous  glands 
such  as  the  deep  glands  of  the  esoph- 
agus. The  ducts  of  the  superficial 
glands,  as  well  as  their  secreting  por- 
tions, and  also  the  lining  epithelium  of 
the  esophagus  upon  which  they  open,  are 
clothed  with  columnar  epithelial  cells. 
Many  of  the  secreting  tubules  contain 
parietal  cells  similar  to  those  of  the  fun- 
dus  glands  of  the  stomach.  Both  ducts 
and  secreting  tubules  contain  small,  cystic 
dilatations. 

At  the  lower  end  of  the  esophagus  a 
similar  group  of  superficial  glands,  the 
lon-er  cardiac  glands  of  the  esophagus,  fre- 
quently mark  the  beginning  transition  to 
the  structure  of  the  cardiac  portion  of  the 
stomach,  with  whose  glands  they  are  con- 
tinuous. 


FIG.  328. — FROM  A  SECTION  OF 

THE  HUMAN  ESOPHAGUS. 
a,  slight  cornification  of  sur- 
face epithelium;  6,  Str.  ger- 
minativum;  c,  L.  propria  mu- 
cosse;  d,  L.  muscularis  mucosae. 
(Goetsch,  Am.  Jour.  Anat.,  10,  1, 
1910.) 


352 


THE  DIGESTIVE  SYSTEM 


The  lining  epithelium  of  the  esophagus  is  of  the  stratified  squamous 
variety.  Its  attached  surface  is  indented  by  the  papilla?  of  the  corium; 
its  free  surface  is  smooth.  In  the  collapsed  state  of  the  organ  its  mu- 
cous membrane  is  thrown  into  longitudinal  folds  or  rugae  and  its  lumen 
is  largely  obliterated.  The  small  isolated  areas  of  columnar  or  ciliated 
epithelium,  which  occur  in  occasional  individuals  on  the  surface  of  the 
esophageal  mucosa,  especially  in  its  upper  third,  are  to  be  regarded 
as  examples  of  irregular  development,  involving  a  persistence  of  the 
ciliated  areas  occurring,  according  to  Johnson  (Amer.  Jour.  Anat.,  10, 
4,  1910),  in  embryos  ranging  from  55  millimeters  to  birth. 

THE  STOMACH 


The  Serous  Coat  (Tunica  serosa). — The  serous  coat  of  the  stomach 
is  derived  from  the  peritoneum.     It  is  formed  by  a  thin  layer  of  sub- 


Lonyittidinal 
section  of  glands 

Tunica  propria 


FIG.  329. — SECTION  THROUGH  THE  STOMACH  WALL  OF  MAN  (PYLORIC  REGION).  X  14. 
(Szymonowicz-MacCallum,  "Histology  and  Microscopic  Anatomy.") 


THE  ALIMENTARY  CANAL  353 

serous  connective  tissue  which  is  covered  by  mesothelium.  The  serous 
coat  supports  the  larger  blood  and  lymphatic  vessels  and  nerve  trunks 
which  supply  the  organ. 

The  Muscular  Coat. — The  muscular  coat  of  the  stomach  consists  in 
general  of  two  layers  of  smooth  muscle  fibers — a  thin  outer  longitudinal, 
and  a  much  thicker  inner  circular  and  oblique  layer.  The  regular  cir- 
cular arrangement  of  these  fibers  is  much  distorted  by  the  peculiar 
dilatation  and  partial  rotation  to  which  the  stomach  is  subjected  in  the 
course  of  its  development,  and  as  a  result  of  this  change  obliquely  placed 
fibers  form  a  considerable  portion  of  the  muscular  coat. 

The  oblique  fibers  are  most  numerous  toward  the  cardiac  end  of  the 
stomach,  where  they  form  a  third  muscular  layer,  the  innermost  portion 
of  the  muscular  coat.  The  longitudinal  fibers  are  most  abundant  toward 
the  cardiac  and  pyloric  orifices  and  along  the  lesser  curvature;  in  the 
fundus  and  mid-region  of  the  stomach  they  form  only  a  very  thin  layer. 
The  circular  fibers  form  the  thickest  of  the  three  muscular  layers  and 
are  nearly  equally  distributed  in  all  portions,  except  that  at  the  cardiac 
and  pyloric  orifices  they  become  much  thickened  to  form  the  sphincter 
muscles.  The  pyloric  sphincter  is  especially  well  developed. 

The  layers  of  the  muscular  coat  of  the  stomach  are  united  by  thin 
septa  of  connective  tissue;  that  between  the  longitudinal  and  circular 
layers  contains  the  myenteric  nerve  plexus  and  the  larger  blood-vessels 
which  supply  this  coat. 

The  Submucosa. — The  submucosa  consists  of  loose  areolar  tissue 
which  supports  the  blood-vessels,  lymphatics,  and  the  submucous  nerve 
plexus,  all  of  which  distribute  their  branches  to  the  mucous  membrane. 
In  no  portion  of  the  stomach  does  this  coat  contain  glands. 

The  Mucous  Coat.— The  muscularis  mucosaB  forms  a  thin  but  com- 
plete layer  from  one  end  of  the  stomach  to  the  other,  and  marks  the 
outer  boundary  of  the  mucous  membrane.  It  usually  consists  of  two 
thin  layers,  an  inner  circular  and  an  outer  longitudinal.  Here  and 
there  muscle  fibers  extend  from  the  muscularis  mucosaB  into  the  corium 
between  the  gastric  glands. 

The  surface  of  the  mucosa  is  clothed  with  tall  columnar  epithelium, 
and  the  whole  membrane  is  thrown  into  wavy  folds,  an  arrangement 
which  is  permitted  by  the  very  loose  meshes  of  the  submucous  areolar 
coat.  The  corium  of  the  mucosa  is  closely  packed  with  tubular  secreting 
glands,  which  open  on  the  surface  by  wide-mouthed,  crypt-like  ducts 
or  foveolae,  and  arc  embedded  in  a  fine  fibroreticular  tissue  containing 
many  lymphocytes. 


354 


THE  DIGESTIVE  SYSTEM 


The  character  of  the  gastric  glands  differs  somewhat  in  various 
portions  of  the  stomach.  The  iliree  varieties,  according  to  their  dis- 

trihution,  are  known 
as  the  'fundus  glands, 
the  pyloric  glands,  and 
the  cardiac  glands. 

THE  FUNDUS 
GLANDS  (Pep  tic 
Glands'). — These  are 
somewhat  branched 
tubular  glands  which 
possess  short  ducts, 
the  crypts  or  foveolce, 
and  relatively  long  se- 
creting portions,  sev- 
eral of  which  open,  by 
means  of  short  con- 
stricted portions,  the 
necks  of  the  glands, 
into  the  bottom  of 
each  crypt. 

The  excretory 
ducts  or  crypts  are 
lined  with  tall  colum- 
nar cells  which  possess 
a  remarkably  clear  cy- 
toplasm distally,  and 
whose  nuclei  lie  at  the 
proximal  or  attached 
ends  of  the  cells.  This 
epithelium  rests  upon 
a  distinct  basement 
membrane  of  reticular 
tissue  (Mall) ;  it  is 


FIG.  330. — THE  MUCOSA  OF  THE  FUNDUS  REGION  OF 
THE  DOG'S  STOMACH. 


o,  gastric  crypts;  b,  neck  region,  and  c,  fundus  por- 
tions of  the  gastric  glands,  the  parietal  cells  being 
much  more  abundant  in  the  former;  d,  muscularis  mu- 
COS3&;  e,  submucosa.  Hematein  and  eosin.  Photo. 
X  80. 

also  continued,  over  that  portion  of  the  corium  which  occupies  the  inter- 
vals between  adjacent  ducts,  where  it  forms  the  true  lining  epithelium  of 
the  stomach.  Its  cells  secrete  a  clear  muco-albuminous  fluid. 

Between  the  distal  ends  of  the  cells  terminal  bars  occur;  they  possess 
also  indistinct  cuticular  borders. 

The  secreting  portion,  or  fundus,  of  the  gland  is  five  to  eight  times 


THE  ALIMENTARY  CANAL 


355 


as  long  as  the  duct  or  foveola,  a  fact  which  sharply  differentiates  the 
fundic  from  the  pyloric  glands  of  the  stomach.  The  lumen  of  the  se- 
creting portion  is  so  narrow  as  to  be 
scarcely  perceptible  except  by  the  use 
of  special  stains  (precipitation  tech- 
nics) or  high  magnification. 

The  fundus  of  the  gland  is  lined 
by  two  distinct  cell  types,  the  chief 
and' the  parietal  cells.  The  chief  cells 
are  relatively  more  abundant  at  the 
deeper  portion  of  the  fundus,  where 
they  form  a  complete  lining  for  the 
tubule.  In  this  portion  the  parietal 
cells  are  crowded  away  from  the  lu- 
men and  consequently  produce  a 
bulging  of  the  basement  membrane. 
Toward  the  neck  of  the  tubule  the 
parietal  cells  are  more  abundant  and 
draw  progressively  nearer  and  nearer 
the  lumen  until,  in  the  neck  of  the 
gland,  they  possess  a  considerable  free 
surface  which  encroaches  upon  the 
glandular  lumen. 

The  Chief  Cells  (Central  Peptic, 
or  Adelomorphous  Cells). — The  chief 
cells  possess  a  cuboidal  or  pyramidal 
shape  and  a  granular  cytoplasm.  The 
spheroidal  nucleus  is  situated  in  the 
proximal  or  attached  end,  while  the 
distal  end  of  the  cell  is  its  most  gran- 
ular portion.  The  breadth  of  the 
granular  zone  is  dependent  upon  the 
state  of  secretory  activity,  the  coarse 
zymogen  granules  accumulating  dur- 
ing periods  of  rest  and  disappearing 
by  secretion  during  activity.  Thus 
the  granular  distal  zone  increases  in 
breadth  during  rest  and  decreases  during  activity.  The  whole  cell  also,  be- 
comes shrunken  after  prolonged  secretion,  but  during  rest  it  becomes  so 
swollen  that  with  its  neighbors  it  nearly  occludes  the  lumen  of  the  tubule. 


FIG.    331. — LONGITUDINAL    SECTION 
OF  THE  FUNDUS  GLANDS  OF  MAN. 
b,  parietal  cells;  g,  fundus  of  the 
gland;  h,  chief  cells;  k,  body,  and  /, 
neck   of   the    gland;    m,    nmscularis 
mucosse;  Mg,  gastric  crypts.     X  85. 
(After  Kolliker.) 


356 


THE  DIGESTIVE  SYSTEM 


The  coarse  zynwyen  granules  within  the  cell  appear  to  he  suspended 
within  the  meshes  of  a  finely  granular  eytoplasmic  reticulum.  At  the 
base  or  proximal  end  of  the  cell  coarse  elongated  granules  or  filaments 
of  prozymogcn  (ergastoplasm  of  Cade)  may  be  demonstrated  by  the 
stronger  basic  or  nuclear  dyes,  e.g.,  iron  hematein,  toluidin  blue.  These 
peculiar  prozymogen  granules  are  so  disposed,  parallel  to  the  axis  of 
the  cell,  as  to  give  this  portion  of  the  cytoplasm  a  somewhat  striated 
or  rodded  appearance  when  carefully  examined  after  suitable  staining. 

The  chief  cells  are  believed 
to    elaborate    the    pepsin 
(pepsinogen)    of  the  gas 
trie  juice. 

The  Parietal  Cells 
(O.ryntic  or  Delomorphous 
Cells)— The  parietal  cells 
- are  lar£e  ov°id  or  pyra- 
midal bodies  which  are 
frequently  binucleated, 
and  whose  cytoplasm  pos- 
sesses a  strong  affinity  for 
acid  dyes  (eosin,  Congo 
red,  etc.).  Their  spherical 
nuclei  contain  much 
chromatin  and  are  cen- 
trally situated;  their  cyto- 
plasm is  homogeneous  or 
finely  granular. 

The  shape  of  the  oxyntic  cells  varies  with  their  location.  At  the 
fundus  of  the  gland  where  they  are  separated  from  the  lumen  by  the 
chief  cells  they  are  ovoid  or  occasionally  triangular  in  transection,  the 
broad  base  of  their  triangular  section  being  applied  to  the  basement 
membrane,  the  wide-angled  tip  wedged  between  the  bases  of  the  adjacent 
chief  cells.  In  the  mid-portion  of  the  secreting  tubule  the  parietal 
cells  approach  nearer  the  lumen,  and  being  inserted  between  the  chief 
cells,  they  acquire  an  increased  height  and  a  pyramidal  form.  At  the 
neck  of  the  gland,  where  they  present  to  the  glandular  lumen  a  broad 
surface,  the  parietal  cells  acquire  a  cuboidal  shape.  As  the  gland  opens 
into  its  foveola  the  parietal  cells,  except  for  an  occasional  dislodged  or 
misplaced  individual,  abruptly  cease. 

In  those  portions  of  the  tubule  where  the  parietal  cells  are  more  or 


FIG.  332. — TRANSECTIONS  OF  THREE  GLANDS  OF 
THE  FUNDUS  REGION  OF  THE  HUMAN  STOMACH. 

The  section  is  taken  from  the  portion  of  the 
glands  near  the  muscularis  mucosac.  The  parietal 
cells  are  red;  the  central  cells,  black.  Hematein 
and  eosin.  X  800. 


THE  ALTMENTAEY  CANAL 


357 


less  removed  from  the  lumen  they  possess  an  extensive  system  of  peri- 
cellular  sen-dory  canals  which  invest  the  cell  in  a  basket-like  manner 
and  convey  its  secretion  to  the  glandular  lumen,  where  it  mixes  with  the 
secretion  of  the  chief  cells.  The  parietal  cells 
also  possess  a  system  of  intracellular  canaliculi. 
The  parietal  cells  are  commonly  believed 
to  secrete  the  HC1  of  the  gastric  juice.  But 
Harvey  and  Bensley  (Biol.  Bull.,  23,  4,  1912) 
claim  to  have  shown 
that  free  HC1  is  not 
present  in  these  cells; 
their  content  is  said  to 
be  chemically  neutral 
or  alkaline,  and  to  con- 
sist largely  of  chlorids. 
The  results  of  experi- 
ments with  rabbits  and 
various  other  verte- 
brates indicate  that 
chlorin  is  secreted  by 
the  parietal  cells  in  the 
form  of  a  chlorid  of  an 
organic  base,  and  that 
the  HC1  is  only  set  free 
after  the  secretion  is 
poured  out  of  the  gland 
into  the  foveola.  Ham- 
mett  (Anat.  Rec.,  9,  1, 
1915),  however,  presents 
further  evidence  tend- 
ing to  show  the  pres- 
ence of  acid  in  the  pari- 
etal cells. 

PYLORIC  GLANDS. — 
These  are  branched  con- 
voluted tubular  glands  with  relatively  long  crypt-like  ducts,  into  the 
bottom  of  which  several  secreting  tubules  open.     According  to  Piersol, 
they  occupy  the  pyloric  fifth  of  the  stomach. 

The  typical  convolution  is  found  only  in  the  fundus  of  the  gland, 
the  course  of  the  ducts  being  nearly  straight,     The  branching,  on  the 


FIG.  333.  —  A  PYLORIC 
GLAND,  FROM  SECTION 
OF  THE  DOG'S  STOMACH. 
(Ebstein.) 

m,  mouth;  n,  neck;  tr,  a 
deep  portion  of  a  tubule 
cut  transversely.  (From 
"Quain's  Anatomy.") 


FIG.  334. — PORTION  OF 
GASTRIC  GLAND 
FROM  THE  FUNDUS 
REGION  OF  THE 
STOMACH. 

L,  lumen,  ending  in 
intracellular  secretory 
canaliculi  in  the  parie- 
tal cells  (P.c.);  C.c., 
chief  cells.  Prepared 
by  the  Golgi  chromate 
of  silver  impregnation 
method;  highly  magni- 
fied. (After  Zimmer- 
mann.) 


358 


THE  DIGESTIVE  SYSTEM 


other  hand,  is  chiefly  confined  to  the  ducts,  which  occupy  the  superficial 
two-thirds  to  three-fourths  of  the  entire  depth  of  the  mucous  membrane. 
In  the  pyloric  mucosa,  therefore,  three  zones  may  be  distinguished:  a 
superficial,  middle,  and  deep. 

The  superficial  zone  is  narrow  and  contains  the  wide-mouthed  crypts 
or  foveolse  which  are  lined  by  tall  columnar 
cells  similar  to  those  of  the  f  undus  crypts. 

The  middle  zone  contains  the  narrowed 
portion  of  the  ducts  and  is  the  broadest  of 
the  three  zones.  Several  of  the  narrow  ducts 
open  into  each  foveola  and  further  branch- 
ing of  the  secreting  tubnles  occurs  to  a  lim- 
ited extent.  The  epithelium  of  the  ducts  is 
of  the  low  columnar  variety,  whose  deeply 
stained  basal  nuclei  are  spheroidal  or  ovoid, 
and  are  progressively  flattened  as  the  se- 
creting portion  is  approached.  The  super- 
ficial cytoplasm  of  these  cells  stains  readily 
with  muchematein  and  often  has  a  coarsely 
granular  or  reticular  appearance. 

The  deepest  zone  contains  the  convoluted 
secreting  portions  and  is  sharply  marked  off 
from  the  adjacent  ducts,  since  in  a  transec- 
tion  of  the  stomach  wall  its  tubules,  owing 
to  their  convolution,  are  nearly  all  cut 
across,  while  the  ducts  are  in  longitudinal 
section;  the  clear  tall  columnar  epithelium 
and  broad  lumen  of  the  fundus  also,  contrast 

strongly  with  the  low  finely  granular  epithelium  and  narrow  lumen 
of  the  duct.  It  is  this  narrow  zone  of  peculiar  convoluted  tubules, 
lying  just  within  the  muscularis  mucosae,  by  which  the  pyloric  mucous 
membrane  is  most  readily  distinguished  from  all  other  regions  of  the 
alimentary  canal. 

The  tall  columnar  cells  of  the  fundus  possess  a  remarkably  clear 
cytoplasm  which  reacts  distinctly,  though  feebly,  to  the  specific  stains 
for  mucus.  The  nuclei  are  flattened  against  the  base  of  the  cell  and 
thus  contrast  sharply  with  the  spheroidal  nuclei  of  the  ducts  and  crypts. 
During  secretion  the  cells  become  shrunken  and  their  nuclei  approach 
the  center  of  the  cell  and  become  more  nearly  ovoid  or  spheroidal  in 
shape. 


FIG.  335. — SECRETORY  CAP- 
ILLARIES OF  THE  FUNDUS 
GLANDS  OF  THE  DOG'S 
STOMACH. 

Golgi  stain.    (After  Miiller, 
from  Oppel.) 


THE  ALIMENTAKY  CANAL 


359 


There  is  no  sharp  line  of  demarcation  between  the  fqpdus  and  pyloric 
regions,  the  glands  offering  a  gradual  transition  from  the  one  type  to 
the  other.  Thus,  in  the  human  stomach,  there  is  a  broad  transition 


FIG.  336. — THE  MUCOSA  OF  THE  PYLORIC  REGION  OF  THE  HUMAN  STOMACH. 
a,  b,  and  c,  respectively  the  crypt,  neck,  and  fundus  zones  of  the  glands;  d,  muscu- 
laris  mucosa;;  e,  subraucosa.     Hematein  and  eosin.     Photo.     X  151. 

zone  which  contains  both  fundus  and  pyloric  glands.  Indeed,  in  many 
individuals,  parietal  cells  may  be  distributed  throughout  almost  the 
entire  rrastric  mucosa. 


360  THE  DIGESTIVE  SYSTEM 

THE  CARDIAC  GLANDS. — A  narrow  region,  about  5  millimeters  in 
width,  at  the  cardiac  orifice  of  the  human  stomach  contains  glands 
whose  form  corresponds  with  that  of  the  fundus  glands,  though  they 
are  slightly  more  branched  and  are  rather  more  tortuous,  but  which 
are  lined  by  relatively  clear  columnar  epithelium.  Only  occasionally 
are  the  chief  and  the  parietal  cells,  which  are  characteristic  of  the  fundus 
glands,  interspersed  among  the  clear  secreting  cells  of  these  tubules. 
The  cardiac  glands,  therefore,  appear  to  offer  a  transition  from  the 
esophageal  to  the  more  numerous  fundus  glands  of  the  stomach.  In 
certain  mammals,  e.g.,  the  pig  and  the  Marsupialia,  the  cardiac  glands 
occupy  a  much  larger  area. 

THE  CORIUM. — The  corium  of  the  mucosa  consists  of  a  delicate 
fibroreticular  connective  tissue  which  supports  the  blood  and  lymphatic 
vessels  and  is  more  or  less  infiltrated  with  lymphocytes.  Hence  in  many 
portions  it  possesses  the  character  of  diffuse  lymphoid  tissue,  though  this 
tissue  is  characteristic  of  the  interglandular  rather  than  the  interfoveolar 
portion  of  the  tunica  propria.  In  the  latter  situation,  in  sharp  contrast 
to  the  intestinal  villi  with  which  the  student  may  confound  this  region, 
the  corium  is  decidedly  fibrous  and  contains  relatively  few  lymph 
corpuscles. 

In  the  deeper  part  of  the  mucosa  occasional  small  lymph  nodules, 
homologues  of  the  solitary  follicles  of  the  intestine,  are  seen.  These 
nodules  ('lenticular  glands']  lie  just  within  the  muscularis  mucosas 
and  do  not,  as  a  rule,  penetrate  into  the  submucosa.  In  the  cardiac 
region  they  may  lie  very  near  the  free  surface  of  the  mucosa. 

Blood  Supply. — The  large  blood-vessels,  derived  from  the  branches 
of  the  celiac  axis,  enter  through  the  subserous  connective  tissue  of  the 
omentum  and  form  arches  at  the  greater  and  lesser  curvatures  of  the 
stomach. 

From  these  arches,  arteries  lying  in  the  subserous  connective  tissue 
are  distributed  to  the  ventral  and  dorsal  surfaces  of  the  gastric  wall. 
These  vessels  supply  branches  which  penetrate  the  muscular  coat,  giving 
off,  on  the  way,  arterioles  to  the  intramuscular  septum,  and  secondarily 
to  the  intramuscular  capillary  plexus,  and  spread  out  in  the  areolar 
tissue  of  the  submucosa  in  which  they  form  an  extensive  arterial  plexus. 
Branches  from  this  submucous  plexus  enter  the  mucous  membrane  and 
form  a  dense  capillary  plexus  whose  elongated  meshes  inclose  the  se- 
•  creting  glands. 

Near  the  surface  of  the  mucosa  these  vessels  enter  a  plexus  of  small 
venules  which,  by  union,  form  larger  branches  and  convey  the  blood 


THE  ALIMENTARY  CANAL 


3G1 


outward  to  a  venous  plexus  at  the  outer  border  of  the  mucosa,  whence 
it  returns  to  the  larger  veins  of  the  submucosa.     These  veins,  after 


M— 


V— 

8— 
Ar- 


0- 


FIG.  337. — BLOOD-VESSELS  AND  LYMPHATICS  OF  STOMACH.  (F.  Mall.) 
M,  mucosa;  Mi,  muscularis  mucosse;  S,  submucosa;  7  and  O,  circular  and  longi- 
tudinal muscles;  A,  blood-vessels,  Ar.,  artery,   V,  vein;  B,  microscopic  anatomy; 
C,   lymphatics.    (From    Szymonowicz-MacCallum,    "Histology    and    Microscopic 
Anatomy.") 

receiving  venules  from  the  muscular  coat,  pass  outward  to  the  subserous 
connective  tissue  in  company  with  the  entering  arteries  and  finally 
reach  the  gastric,  splenic,  and  portal  veins. 


362 


THE  DIGESTIVE  SYSTEM 


The  Lymphatics. — The  lymphatics  arise  by  vascular  loops  or  dilated 
extremities  between  the  secreting  glands  of  the  mucosa.  At  the  outer 
border  of  the  mucous  membrane  they  form  a  delicate  anastomosing 
plexus  from  which  branches  penetrate  the  muscularis  mucosac  and 
enter  a  broad  submucous  plexus  whose  efferent  vessels  pierce  the  mus- 
_  cular  coat  on  their  way  to  lymph 

nodes  which  are  situated  in  the 
folds  of  the  omentum  at  either 
curvature  of  the  stomach. 

The  Nerves. — The  nerves  of 
the  stomach  are  derived  from  sym- 
pathetic trunks,  the  splanchnic 
nerves,  and  from  the  vagi.  The 
vagi  are  believed  to  be  chiefly  ex- 
citatory, the  splanchnics  inhibitory 
in  function.  The  nerves  enter 
with  the  blood-vessels  and  pierce 
the  muscular  coat.  They  connect 
with  two  plexuses  of  anastomosing 
nerve  trunks:  the  myenteric 
(AueibachV),  in  the  intramuscular 
fibrous  septum,  which  contains 
ganglionic  enlargements  at  many 
of  its  intersections  and  distributes 


FIG. 


338. — TERMINATION    OF    SYMPA- 
THETIC NERVE  FIBERS. 


A,  on  smooth  muscle  cell;  B,  on  cells 
of  the  digestive  epithelium,  ileum  of  cat; 
C,  on  cells  "of  the  digestive  epithelium, 
stomach  of  cat ;  D,  on  parietal  cell,  stom- 
ach of  cat.  (Kuntz,  Jour.  Comp.  Neur., 
23,  3,  1913.) 


its  fibrils  to  the  smooth  muscle; 
the  submucous  (Meissncr's),  lying 
in  the  deeper  part  of  the  submucosa, 
which  also  contains  small  ganglia 

at  the  intersections  of  its  anastomosing  branches.  This  latter  plexus  is 
much  finer  and  contains  smaller  neurons  than  that  of  the  muscular  coat. 
Pericellular  capsules  are  apparently  lacking  in  these  plexuses  (Miiller, 
Kuntz).  The  submucous  plexus  distributes  its  fibrils  to  the  mucosa, 
where  they  terminate  in  and  about  the  walls  of  the  blood  and  lymphatic 
vessels,  and  to  the  epithelium  of  the  secreting  glands,  where 'they  end 
as  varicose  fibrils  upon  the  cells.  Kuntz  (Jour.  Comp.  Neur.,  23,  3, 
1913)  suggests  that  the  ganglia  of  the  myenteric  and  submucous  plexus 
include  both  motor  and  sensory  neurons,  and  that  the  fibers  which 
terminate  on  cells  of  the  digestive  epithelium  are  the  dendrons  of  sen- 
sory cells. 


THE  ALIMENTARY  CANAL 


363 


<&X     VE/     \QS    VJ& 

FIG.  339. — SCHEMATIC  DIAGRAM  ILLUSTRATING  PROBABLE  RELATIONSHIP  OF  SYM- 
PATHETIC NEURONS  IN  MYENTERIC  AND  SUBMUCOUS  PLEXUSES. 

Motor  neurons,  stippled;  sensory  neurons,  solid.  1,  tunica  propria;  2,  muscularis 
mucosse;  3,  submucosa;  4,  muscularis;  M,  my  enteric  plexus;  *S,  submucous  plexus; 
a,  axons;  d,  dendrons.  (Kuntz,  Jour.  Comp.  Neur.,  23,  3,  1913.) 


SMALL  INTESTINE 

The  small  intestine  constitutes  the  longest  portion  of  the  digestive 
tube.  It  connects  the  pylorus  with  the  colon.  It  measures  about  7}/2 
meters  (24  feet)  in  length.  It  may  be  divided  into  three  segments:  (1) 
the  duodenum,  about  11  inches  in  length;  (2)  the  jejunum,  including 
the  upper  two-fifth,  about  9  feet,  and  (3)  the  ileum,  including  the 
lower  three-fifth,  about  14  feet,  of  the  remainder.  The  duodenum 
lacks  a  mesentery,  it  is  only  partially  enveloped  by  a  serosa,  and  it  has 
the  greater  diameter,  about  47  millimeters  (2  inches).  Below  the 
duodenum  the  caliber  of  the  small  intestine  gradually  decreases  until 


364 


THE  DIGESTIVE  SYSTEM 


a  diameter  of  27  millimeters  (a  little  over  1  inch)  is  attained,  at  the 
end  of  the  ileum.  The  three  portions  differ  also  in  the  shape  and 
number  of  villi,  and  in  other  histologic  details  which  will  be  described 
below.  The  inner  surface  is  modeled  by  a  succession  of  tall  circular 

folds,  the  valvulcB  conni- 
ventcs  or  plicce  circularcs, 
involving  the  submucous 
layer.  These  plica3  be- 
come less  closely-spaced 
throughout  the  lower 
portion  of  the  ileum  and 
generally  disappear 
toward  its  end.  They 
serve  to  increase  the  ab- 
sorbent surface  of  the 
intestinal  mucosa,  and 
unlike  the  villi,  which 
are  scattered  over  their 
surface,  they  are  not  sub- 
ject to  variations  depen- 
dent upon  altering  de- 
grees of  distention. 

The  structure  of  the 
serous  coat  of  the  small 
intestine  is  identical  with 
that  of  the  stomach.  The 
muscular  coat  consists  of 
an  inner  and  an  outer 
layer  of  unstriped  muscle 
fibers  which  are  sep- 
arated by  a  thin  connec- 
tive tissue  septum.  The  inner  circular  layer  is  much  thicker  than  the 
outer  longitudinal. 

The  regular  disposition  of  the  muscle  fibers  as  an  outer  longitudinal 
and  an  inner  circular  layer  serves  as  a  guide  to  the  recognition  of  the 
direction  in  which  a  given  microscopical  section  has  been  cut.  In  transec- 
tions  of  the  intestine  the  muscle  fibers  of  the  outer  layer  of  the  mus- 
cular coat  are  transversely  cut;  in  longitudinal  sections  o'f  the  organ 
the  same  fibers  are  seen  in  longitudinal  section. 

The  Submucosa. — The  submucosa  of  areolar  connective  tissue  is 


FIG.  340. — SECTION  THROUGH  THE  COMMENCEMENT 
OF  THE  DUODENUM  AT  THE  PYLORUS.  (Klein.) 

v,  villi;  b,  apex  of  a  lymphoid  nodule;  c,  crypts  of 
Lieberkiihn;  m,  muscularis  mucosae;  s,  secreting 
tubes  of  Brunner's  glands;  d,  ducts  of  pyloric  glands 
of  stomach;  g,  tubes  of  these  glands  cut  across  in 
mucous  membrane;  t,  deep-lying  tubes  situated  in 
submucous  tissue,  and  corresponding  with  Brun- 
ner's glands  of  the  intestine.  (From  Quain's  "Anat- 
omy.") 


THE  ALIMENTARY  CANAL 


365 


identical  with  that  of  the  stomach  except  in  the  duodenum  where  it 
is  penetrated  hy  the  branched  tubulo-acinar  mucous  duodenal   (Brun- 


vm 


Gland  of  Lieberkii 


Musrn!aris  mncosie 

Duct  of  Brunner's 
gland 


Circular  muscle  layer 


Ganglion  cells  of 
Auerbach's  jilc.fnn 


Longitudinal  muscle 
layer 


FIG.  341. — FROM  A  LONGITUDINAL  SECTION  THROUGH  THE  DUODENUM  OP  A  CAT. 

X  34. 

(From  Szymonowicz-MacCallum,  "Histology  and  Microscopic  Anatomy.") 

HIT'S)    glands.     The  muscularis  mucosse   forms   a   complete  muscular 
layer  and,  except  in  the  duodenum,  is  not  penetrated  by  the  glands. 


366  THE  DIGESTIVE  SYSTEM 

The  Mucous  Membrane. — The  mucous  membrane  of  the  small  in- 
testine is  divisible  into  an  inner  and  an  outer  zone.  In  the  inner  zone 
the  corium  forms  finger-like  projections,  the*intestinal  villi,  which  are 
covered  with  tall  columnar  epithelium  containing  many  mucus-secreting 
goblet  cells.  The  villi  are  characteristic  of  the  small  intestine,  in  which 
alone  they  occur.  They  serve  to  increase  the  area  of  the  lining  epi- 
thelium of  the  intestine,  whose  chief  function  is  that  of  absorption. 

The  outer  zone  of  the  mucous  membrane  includes  all  that  portion 
between  the  muscularis  mucosae  and  the  bases  of  the  intestinal  villi.  It 
is  almost  completely  occupied  by  the  simple  tubular  intestinal  glands 
(or  crypts  of  Lieberkiihn). 

THE  CORIUM. — The  corium  of  the  small  intestine,  in  which  the 
intestinal  glands  are  embedded,  and  which  forms  the  substance  of  the 
intestinal  villi,  consists  of  a  fibroreticular  stroma  which  is  so  infiltrated 
with  lymphocytes  as  to  form  a  diffuse  lymphoid  tissue.  In  many  parts 
of  the  mucosa  the  lymphoid  tissue  forms  isolated  nodules,  the  solitary 
nodules,  or  aggregations  of  such  nodules,  which  are  known  as  the  agmi- 
nate nodules  or  Peyer's  patches.  Solitary  nodules  occur  throughout 
both  the  large  and  the  small  intestine.  Peyer's  patches  are  found  only 
in  the  small  intestine  and  are  most  numerous  in  the  upper  portion  of  the 
ileum. 

Structure  of  the  Solitary  Nodules. — The  structure  of  the  solitary 
nodules  does  not  differ  from  that  of  other  lymph  nodules.  They  vary 
much  in  size,  most  of  them  being  of  sufficient  diameter  to  occupy 
the  entire  thickness  of  the  mucous  membrane.  They  push  aside  the 
adjacent  intestinal  glands  by  which  they  are  encircled,  and  few  or  no 
villi  project  from  their  free  surface.  The  adjacent  villi  are  so  inclined 
that  their  free  ends  often  hide  all  but  the  projecting  apex  of  the  ovoid 
solitary  nodule. 

The  largest  of  the  solitary  nodules  not  only  produce  a  distinct  ele- 
vation of  the  surface  of  the  mucous  membrane  but  may  even  break 
through  the  muscularis  mucosae  and  project  into  the  connective  tissue 
of  the  submucosa.  The  solitary  nodules,  like  other  lymph  nodules, 
usually  contain  a  germinal  center. 

Agminate  Nodules  (Aggregate  Nodules;  Peyer's  Patches}. — Agmin- 
ate nodules  are  formed  by  accumulations  of  lymph  nodules,  usually 
occurring  in  that  portion  of  the  intestinal  mucosa  which  is  farthest 
removed  from  the  attachment  of  the  mesentery.  They  frequently 
form  oval  areas  of  macroscopic  size.  They  usually  number  about  thirty, 
though  there  may  be  fewer,  and  frequently  many  more.  The  numbei 


THE  ALIMENTARY  CANAL 


367 


of  their  constituent  nodules  is  variable,  frequently  they  contain  as  many 
as  fifteen  or  twenty.  Each  of  these  nodules  is  usually  invested  by  a  thin 
fibrous  capsule,  though  frequently  they  are  confluent  with  one  another. 


FIG.  342. — THE  CENTRAL  PORTION  OP  A  PEYER'S  PATCH  IN  THE  ILEUM  OF  A  DOG'S 
INTESTINE. 

a,  villi;  b,  glands;  c,  lymph  nodules,  an  agminated  follicle;  d,  connective  tissue  of 
the  submucosa;  e,  a  portion  of  the  muscular  coat.  Hematein  and  eosin.  Photo. 
X  35. 

The  long  axes  of  the  ovoid  nodules  exceed  the  average  thickness  of 
the  mucous  membrane  so  that  the  patch  forms  a  superficial  elevation  of 
the  mucosa  and  its  deeper  surface  penetrates  the  muscularis  mucosae 
and  enters  the  submucous  coat.  Hence  occasional  fragments  of  the  mus- 
cularis mucosEe  often  occur  between  the  bases  of  the  constituent  nodules. 


368 


THE  DIGESTIVE  SYSTEM 


Villi  are  found  upon  the  free  surface  of  the  agminate  nodules  only 
in  the  intervals  between  the  constituent  units.  The  largest  of  the 
nodules  lie  near  the  center  of  the  patch,  the  smallest  are  found  at  its 
periphery.  The  agminate  nodules  become  the  chief  seats  of  infection  in 
typhoid  fever. 

Above  the  level  of  the  ileum  the  largest  collections  of  lymphoid 
tissue  in  the  intestinal  mucosa  occur  in  the  upper  part  of  the  duo- 
denum, where  there  are  extensive  infiltrations  of  dense  lymphoid  tissue, 
many  of  which  contain  typical  nodules  with  germinal  centers.  These 

masses  of  lymphoid  tissue  are 
penetrated  by  the  ducts  of  the 
duodenal  glands,  whose  secret- 
ttetit  ing  portions  form  a  bed  upon 
which     the     lymphoid     tissue 
,tiaaf  rests.     The   duodenal   patches 
differ  slightly   from   those  in 


FIG. 


morc  confluent  mass  with  rela- 
343,-DiAGRAM   OF   SMALL   INTESTINE,     tively  fewer  nodules ;  they  also 


SHOWING  THE  TOPOGRAPHICAL  RELATION-    possess  a  more  diffuse  charac- 
SHIP  OF  THE  INTESTINAL  GLANDS  (CRYPTS    *  ,       ,       .,      ,    , 

OF  LiEBERKtJHN)  TO  THE  VILLI.  ter,  are  more  deeply  situated, 

and  are  therefore  covered  by 
the  corium  of  the  mucosa  which  contains  both  intestinal  glands  and 

vim. 

THE  INTESTINAL  VILLI. — The  intestinal  villi  are  long  finger- 
like  projections  (from  0.5  to  1  millimeter  in  length)  which  vary 
much  in  form  in  different  mammals  and  in  different  portions  of  the 
canal  in  the  same  individual.  They  are  perhaps  most  highly  developed 
in  the  dog,  where  they  form  long  projections  with  expanded  or  clubbed 
extremities  and  a  constricted  base  or  neck. 

In  man  the  villi  are  of  a  more  conical  shape,  the  base  being,  as  a 
rule,  slightly  broader  than  the  free  extremity.  In  the  duodenum  of 
man  they  possess  a  foliate  shape,  in  the  jejunum  they  are  conical  or 
somewhat  clavate,  in  the  ileum  they  are  generally  filiform.  The  villi 
are  most  abundant  in  the  duodenum  and  the  jejunum  (24  to  40  per 
square  millimeter)  and  less  numerous  in  the  ileum  (15  to  30  per  square 
millimeter)  (Piersol).  According  to  Johnson  (Amer.  Jour.  Anat.,  14, 
2,  1913)  they  are  more  or  less  variable  structures,  their  shape  and 
height  changing  with  the  degree  of  distention  of  the  tube. 


THE  ALIMENTARY  CANAL 


3G9 


The  villus  is  formed  by  a  projection  of  the  corium  which  is  cov- 
ered by  the  lining  epithelium  of  the  intestine.  The  axis  of  the  villus 
contains  a  large  lymphatic  capillary  or  lacteal,  which  begins  in  the 
inner  third  and  proceeds  outward  through  the  corium  to  enter  a  lym- 
phatic plexus  lying  just  within  the  muscularis  mucosa3.  An  occasional 
villus  may  contain  several  lacteals.  In  the  base  or  outer  portion  of 
the  villus  the  lacteal  is  surrounded  by  small  groups  of  smooth  muscle 
fibers  which  are  disposed  in  an  axial 
direction,  and  which  are  ontogenet- 
ically  derived  from  the  muscularis  mu- 
cosae.  Many  of  these  fibers  turn  out- 
ward and  are  attached  to  the  basement 
membrane  beneath  the  epithelium  at 
the  sides  and  tip  of  the  villus.  By 
their  rhythmic  contraction  the  muscle 
fibers  of  the  villus  aid  in  expelling  the 
contents  of  the  lacteal. 

The  body  of  the  villus  consists  of 
diffuse  lymphoid  tissue  having  a  reticu- 
lar  stroma  in  which  the  lacteal,  the 
muscle  fibers,  and  the  blood-vessels  are 
embedded. 

Each  villus  is  supplied  with  one  or 
more  arterioles  which  enter  at  the  base 
and  pass  to  the  inner  third,  where  they 
form  an  abundant  capillary  plexus 

about  the  blind  extremity  of  the  lacteal  and  in  the  apex  of  the  villus. 
Minute  venules  collect  the  blood  from  this  plexus,  and  following  the 
course  of  the  lacteal,  make  their  exit  from  the  base  of  the  villus  to  join 
the  venous  plexus  in  the  deeper  part  of  the  mueosa  (Fig.  347). 

The  Lining  Epithelium. — The  lining  epithelium  of  the  intestine, 
which  also  clothes  the  villi,  rests  upon  a  distinct  reticular  basement 
membrane  and  consists  of  columnar  and  goblet  cells.  The  large  num- 
ber and  peculiar  appearance  of  the  goblet  cells  is  highly  characteristic 
of  this  tissue. 

The  columnar  cells  are  peculiar  in  that  they  possess  a  characteristic 
striated  cuticular  border  when  examined  under  moderately  high  magni- 
fication. They  possess  a  finely  reticulated  cytoplasm  and  an  ovoid 
nucleus  which  is  situated  at  the  proximal  end  or  base  of  the  cell.  Fre- 
quently the  cytoplasm  contains  droplets  of  fat  which  are  in  process 


FIG.  344. — LONGITUDINAL  SECTION 
OF  VILLUS. 

G,  goblet  cell;  L,  lacteal;  s,  stri- 
ated border  of  columnar  cell. 


370 


THE  DIGESTIVE  SYSTEM 


of  absorption.  Occasional  leukocytes  find  their  way  into  the  epithelial 
coat,  whence  they  may  penetrate  the  intercellular  substance  and  enter 
the  intestinal  canal. 

THE  INTESTINAL  GLANDS  (Glands  of  Lieberkuhn;  Mucous  Crypts). 
— The  intestinal  glands  occur  throughout  the  entire  extent  of  the  small 
and  large  intestines,  including  the  appendix.  They  are  simple  tubules 


FIG.  345. — SEVERAL  VILLI  FROM  THE  SMALL  INTESTINE  OF  THE  DOG,  IN  LONGITU- 
DINAL SECTION. 

a,  villi;  6,  crypts  of  Lieberkuhn.    Hematein  and  eosin.    Photo.    X  185. 

which  extend  the  whole  depth  of  the  mucous  membrane  and  in  the 
small  intestine  open  upon  the  free  surface  between  the  bases  of  the 
villi.  Hence  the  lining  epithelium  of  the  glands  becomes  continuous 
with  that  which  clothes  the  villi.  The  glands  are  imbedded  in  the 
diffuse  lymphoid  tissue  of  the  corium;  they  rarely  branch.  They  con- 
sist of  a  lining  epithelium  and  a  basement  membrane. 

The  epithelium  of  the  glands  contains  three  types  of  cella:  (1) 
columnar  cells;  (2)  goblet  cells;  and  (3)  the  granule  cells  of  Paneth. 
The  columnar  and  goblet  cells  resemble  those  which  clothe  the  villi. 
The  columnar  cells  which  line  the  neck  of  the  glands,  however,  possess 


-THE  ALIMENTAEY  CANAL  371 

only  a  very  indistinct  cuticular  border  and  such  border  is  entirely 
lacking  in  the  fundus  cells  of  the  glands.  The  epithelium  of  the  glands 
appears  to  take  no  part  in  the  process  of  absorption  and  therefore  con- 
tains no  fat  globules.  It  secretes  a  mucous  fluid. 

At  the  neck  of  the  gland  the  epithelium  frequently  contains  mitotic 
figures  which  have  been  demonstrated  in  man  (Schaffer,  1897)  as  well 
as  in  the  lower  mammals  (Bizzozero,  1887).  Little  or  no  mitosis  has 
been  demonstrated  in  the  fundus  of  the  gland  or  upon  the  free  surface 
of  the  villi.  On  these  facts  the  so-called  wander  theory  of  Bizzozero 
is  founded.  According  to  this  theory  there  exist  in  the  neck  of  the 
glands  certain  indifferent  cells  which  are  capable  of  reproduction  by 
mitosis  and  whose  daughter-cells  move  toward  the  free  surface,  being 
at  the  same  time  differentiated  into  either  the  goblet  or  the  columnar 
cells  of  the  villi. 

Bizzozero  originally  considered  that  the  granule  cells  of  Paneth  at 
the  fundus  of  the  glands  were  intermediate  phases  in  the  formation 
of  goblet  cells,  but  as  there  is  little  or  no  mitosis  in  the  region  where 
these  peculiar  cells  occur  and  as  the  granule  cells  are  never  displaced 
toward  the  surface,  it  seems  more  probable  that,  as  also  in  the  gastric 
glands,  the  indifferent  genetic  cells  of  the  neck  of  the  tubule  develop 
on  the  one  hand  the  superficial  goblet  and  columnar  cells  which  clothe 
the  villi,  and  on  the  other  hand,  the  true  secreting  cells  in  the  fundus 
of  the  intestinal  glands. 

The  granule  cells  of  Paneth  (Arch.  f.  mikr.  Anat.,  1888)  are  con- 
fined to  the  extreme  tip  or  blind  extremity  of  the  fundus  of  the  glands. 
They  are  pyramidal  or  low  columnar  cells  whose  spheroidal  nuclei  are 
situated  close  to  the  basement  membrane.  Their  cytoplasm  presents 
a  delicate  reticulum  which  is  filled  with  coarse  granules  which  in  some 
cells  are  of  a  basophil  nature  (Klein,  Amer.  Jour.  Anat.,  1906).  In 
others  they  contain  still  coarser  granules  which  are  strongly  eosinophil. 
The  exact  function  of  these  peculiar  cells  is  unknown,  but  that  they  are 
true  secreting  cells  seems  highly  probable. 

Still  other  types  of  granular  cells  of  unknown  significance  have 
recently  been  described  by  Kull  (Arch.  mikr.  Anat.,  81,  3,  1913)  in  the 
fundus  of  the  intestinal  glands,  and  among  the  epithelial  cells  clothing 
the  villi:  (1)  'acidophil  cells,'  with  the  basal  oxyphilic  granules  finer 
than  those  of  the  Paneth  cells;  and  (2)  'chromaffin  cells'  with  yellowish 
basal  granules,  coarser  than  those  of  the  acidophil  cells  and  finer  than 
those  of  the  cells  of  Paneth.  These  three  types  of  cells  are  present  in 
man  and  certain  vertebrates;  they  are  said  to  have  no  genetic  relation- 
24 


372 


THE  DIGESTIVE  SYSTEM 


ship.  The  'chromaffin  cells'  of  the  intestinal  epithelium  were  first 
recognized  by  Schmidt,  who  designated  them  as  'yellow  cells'  (Arch, 
mikr.  Anat.,  Bd.  66,  1905).  Ciacco  (Arch.  Anat.  e  Embri.,  6,  3,  1907) 
reports  similar  cells  also  in  the  duodenal  (Brunner's)  glands.  Chanipy 
(Compt.  rend.  Soc.  Biol.,  T.  66,  1909)'- 
has  described  also  mitochondria  in  the 
cells  of  the  intestinal  glands. 

The  intestinal  glands  are  confined  to 
the  narrow  deeper  zone  of  the  intestinal 
mucous  membrane.  Their  lumen,  after 
fixation,  contains  only  the  coarsely  reticu- 
lar  mucous  secretion. 

The  student  should  be  warned  to  dis- 
tinguish carefully  between  the  transverse 
sections  of  the  tubular  glands  which  are 
confined  to  the  deep  zone  of  the  mucous 
membrane  and  the  similar  sections  of  the 
villi  which  are  only  found  in  the  super- 
ficial zone  and  whose  epithelial  coat,  in- 
stead of  inclosing  a  mere  reticular  mass 
of  mucous  secretion  invests  an  organized 
body  of  diffuse  lymphoid  tissue. 

THE  DUODEXAL  (BRUXNER'S)  GLANDS. 
— The  duodenal  glands  of  Brunner  are 
tubulo-acinar  glands  which  furnish  a 
muco-albuminous  secretion.  They  appear 
to  represent  the  continuation  into  the  in- 
testine of  the  pyloric  glands  of  the  stom- 
ach, and  they  occur  in  decreasing  propor- 
tion throughout  the  entire  length  of  the 
duodenum;  around  the  duodenal  papilla?, 
however,  they  become  locally  more  numer- 
ous. They  are  sharply  distinguished  from  the  pyloric  glands  by  their 
larger  size.  Moreover,  the  secreting  portion  of  the  duodenal  glands  is 
only  found  in  the  submucosa  and  the  deeper  part  of  the  mucous  mem- 
brane, where  the  secreting  acini  form  very  numerous  groups,  the  tu- 
bules of  each  of  which  are  connected  with  the  terminal  subdivision  of  a 
duct. 

The  ducts  of  the  duodenal  glands  open  on  the  free  surface  between 
the  villi  by  means  of  crypt-like  tubules  which  are  lined  by  tall  columnar 


FIG.  346.  —  RECONSTRUCTION 
MODEL  OF  A  BRUNNER'S 
GLAND,  FROM  THE  HUMAN 
DUODENUM. 

Three  partially  blended  ducts 
pass  into  the  submucosa  and  end 
in  expanded  alveoli.  X  344. 
(After  Maziarski.) 


THE  ALIMENTARY  CANAL 


373 


epithelium  and  can  only  with 
difficulty  be  distinguished  from 
the  adjacent  intestinal  glands. 
In  the  deeper  part  of  the  mu- 
cous membrane  the  ducts 
branch  and  pursue  a  somewhat 
tortuous  course  to  the  fundus 
of  the  gland,  where  the  ter- 
minal acini  of  each  subdivi- .!::i 
of  a  duct  are  invested  with  a 
distinct  fibrous  capsule. 

The  secreting  epithelium 
of  the  duodenal  glands  consists 
of  tall  columnar  cells  which 
surround  a  wide  lumen.  When 
loaded  with  secretion  the  cells 
are  swollen  and  clear,  but  be- 
come shrunken  and  granular 
after  a  period  of  activity. 
Their  cytoplasm  reacts  to  the 
specific  stains  for  mucin  only 
when  these  are  applied  for  a 
considerable  time  in  concen- 
trated solution  (Bensley).  The* 
spheroidal  nucleus  is  situated 
at  the  proximal  or  basal  end, 
and  as  the  cell  fills  with  secre- 
tion the  nucleus  becomes  pro- 
gressively flattened. 

Blood  Supply.— The  blood 
supply  of  the  small  intestine 
resembles  that  of  the  stomach. 
The  branches  of  the  mesenteric 
arteries  pass  around  the  intes- 
tinal wall  in  the  subserous  con- 
nective tissue.  From  this  point 
they  penetrate  the  muscular 
coat  to  form  intramuscular  and 
submucous  plexuses.  From 
the  latter  a  few  branches  sup- 


FIG.  347. — THE  BLOOD-VESSELS  OF  THE 
SMALL  INTESTINE  OF  A  DOG,  DRAWN  AFTER 
AN  INJECTED  PREPARATION. 

The  arteries  are  striped,  the  veins  black, 
the  capillaries  open.  A,  villi;  B,  glands;  C, 
muscularis  mucosse;  D,  submucosa;  E,  cir- 
cular, and  F,  longitudinal  layer  of  the  mus- 
cular coat;  a,  venule  beginning  from  the  cap- 
illaries of  the  villus,  and  at  6,  from  those 
among  the  glands;  c,  artery  to  the  villus;  d, 
venules  in  the  deeper  part  of  the  mucosa;  e, 
main  arterial  trunk  to  several  adjacent  villi; 
/,  arterial  branch  to  the  glandular  region. 
Highly  magnified.  (After  Mall,  from  Oppel.) 


374  THE  DIGESTIVE  SYSTEM 

ply  the  adjacent  portion  of  the  inner  layer  of  the  muscular  coat,  but  most 
of  them  pass  to  the  mucous  membrane,  in  which  a  plexus  lies  just  within 
the  muscularis  mucosse  and  distributes  its  branches  to  the  capillaries 
about  the  intestinal  glands  and  to  the  intestinal  villi. 

The  artery  of  the  villus  enters  at  its  base,  and  distributing  capillaries 
along  its  course,  forms  in  the  distal  part  of  the  villus  an  abundant 
capillary  network  from  which  efferent  venules  return  by  a  similar  course. 
The  artery,  however,  is  found  near  the  axis,  the  venules  near  the  per- 
iphery of  the  villus. 

Branches  from  the  submucous  and  mucous  arterial  plexuses  also 
supply  capillaries  to  the  duodenal  glands  in  the  duodenum  as  well  as  to 
the  solitary  and  agminated  lymph  nodules.  About  each  of  the  lymph 
nodules  they  form  circular  anastomoses,  from  which  radial  capillaries 
are  distributed  within  the  nodule. 

The  veins  pursue  a  course  exactly  similar  to  that  of  the  arteries.  On 
their  way  to  the  mesenteric  vessels  they  form  mucous,  submucous,  intra- 
muscular, and  subserous  plexuses,  and  drain  into  the  portal  system. 
The  portal  vein  and  its  main  tributaries  lack  valves.  Valves  are  present 
only  in  the  smaller  tributaries,  beginning  in  the  tunica  muscularis 
throughout  the  digestive  tube  and  prevailing  generally  in  the  mesenteric 
veins. 

Lymphatics. — The  lymphatics  or  lacteals  of  the  small  intestine  be- 
gin in  the  distal  part  of  the  villi  as  lymphatic  capillaries,  each  having, 
as  a  rule,  a  pouched,  blind  extremity.  'During  the  digestion  of  fats 
they  become  distended  with  a  whitish  fatty  lymph  called  chyle.  At  their 
origin  the  lacteals  are  frequently  branched,  or  they  may  even  form 
a  scanty  anastomosis.  They  finally  unite  to  form  a  central  lacteal  in 
the  axis  of  the  villus,  which  empties  into  a  rich  plexus  about  the  intes- 
tinal glands,  or  like  the  efferent  vessels  of  this  plexus,  they  may  pass 
directly  to  the  larger  lymphatic  vessels  of  the  submucosa. 

From  the  submucous  plexus  numerous  efferent  lymphatic  vessels 
penetrate  the  muscular  coat,  receiving  the  lymph  from  the  vessels  of 
the  intramuscular  septum.  They  empty  into  the  larger  lacteal  vessels 
of  the  mesentery  which  are  intimately  connected  with  numerous  mesen- 
teric lymph  nodes.  In  the  mucosa  and  submucosa  the  lacteals  form 
sinuses  which  surround  the  bases  of  the  solitary  and  agminated  nodules. 
Thus,  much  of  the  chyle  is  permitted  to  come  into  relation  with  the 
parenchyma  of  these  organs  before  leaving  the  intestinal  mucosa. 

Nerve  Supply. — The  nerve  supply  of  the  intestine  is  exactly  similar 
to  that  of  the  stomach.  The  non-medullated  fibers  form  an  intra- 


THE  ALIMENTAEY  CANAL 


375 


muscular  my  enteric  ganglionic  plexus  (Auerbach's)  for  the  supply  of 
the  muscular  coat,  and  a  submucous  plexus  (Meissner's)  which  sup- 
plies branches  to  the  blood-vessels  and  to  the  glands  of  the  mucosa. 
The  finer  branches  in  the  mucous  membrane  penetrate"  to  the  villi,  form- 
ing a  delicate  plexus  of  naked  fibrils  about  its  blood-vessels  and  lacteals, 
and  upon  its  epithelium. 

Intestinal  Absorption. — The  absorption  of  fat  consists  essentially 
of  three  phases:  (1)  its  absorption  into  the  intestinal  epithelium;  (2) 


FIG.  348. — INTESTINAL  MUCOSA  OF  A  FROG  DURING  THE  ABSORPTION  OF  FAT. 

a,  epithelium;  b,  tunica  propria;  c,  an  ameboid  leukocyte.     Osmium  tetroxid. 
Highly  magnified.     (After  Schafer.) 


its  secretion  into  the  lymphoid  tissue  of  the  villus;  and  (3)  its  entrance 
into  the  lacteal  vessels.  In  an  animal  killed  during  the  absorption  of 
fat,  the  intestinal  villi,  after  fixation  by  solutions  of  osmium  tetroxid, 
contain  fat  in  (a)  the  epithelium,  (b)  the  lymphoid  tissue,  and  (c)  the 
central  lacteal. 

In  the  epithelium,  fat  is  contained  in  the  form  of  fine  droplets 
which  are  most  numerous  in  the  distal  or  free  ends  of  the  cells.  They 
are  also  found  in  the  intercellular  spaces.  During  absorption  the  epi- 
thelial cells  of  the  villi  become  much  swollen  and  elongated.  As  the 
process  subsides  they  return  to  their  former  size,  and  become  relatively 
shrunken.  When  most  distended  the  intracellular  fat  droplets  are  the 


376 


THE  DIGESTIVE  SYSTEM 


most  abundant;  as  the  cells  shrink  the  intercellular  droplets  increase 
relatively  in  number  (Drago,  Eicherche  d.  lab.  ant.  norm.  d.  r.  univ.  d. 
Eoma,  1900).  The  relative  size  of  the  epithelial  cells  and  the  abun- 
dance of  intra-epithelial  fat  is  apparently  dependent  upon  the  activity 
of  the  processes  of  absorption. 

As  to  the  manner  in  which  the  fat  enters  the  epithelium  there  is 
some  doubt.  Schafer  (Internat.  Monatsch.  f.  Anat.  u.  Physiol.,  1885) 
suggested  that  the  leukocytes  by  their  ameboid  activity  inclose  the 

emulsified  droplets  in  the 
intestinal  lumen  and  convey 
them  into  the  substance  of 
the  villi.  It  seems  more 
probable  that  the  fats  are 
saponified  in  the  intestinal 
tract,  and  enter  the  epithe- 
lium in  solution  (White- 
head.,  Amer.  Jour.  Physiol., 
24,  2,  1909).  Here  they 

Y;q  ,' ^  -V.  ••"••'       "  are  again   synthesized   into 

•  \  v  A: /•'•;'' ii:     '  neutral  fat  by  the  activity 

of  the  epithelium  (Pniiger, 
Arch.  f.  d.  ges.  Physiol., 
1900).  Such  a  process  ac- 
counts for  the  abundance  of 
fat  within  the  distal  por- 
tions of  the  cells.  The  drop- 
lets are  then  secreted  into 
the  intercellular  and  subja- 
cent tissue  spaces. 

The  second  phase  of  absorption  includes  the  transference  of  the 
fat  particles  to  the  lacteal.  This  process  appears  to  depend  partially,  at 
least,  upon  the  activity  of  the  leukocytes,  as  suggested  by  Schafer,  the 
particles  of  fat  thus  finding  their  way  through  the  diffuse  lymphoid 
tissue.  According  to  Eeuter  (Anat.  Hefte,"  1902),  fat  droplets  are 
found  in  the  tissue  spaces  as  well  as.  in  the  lymph  corpuscles  of  the 
diffuse  lymphoid  tissue,  a  fact  which  would  seem  to  indicate  that  other 
agencies  aid  in  the  transit  of  the  fat  from  the  epithelium  to  the  lacteal 
than  are  accounted  for  by  the  purely  mechanical  theory  of  Schafer. 
The  third  phase  includes  the  secretion  of  the  fat  into  the  lumen  of 
the  lacteal;  this  is,  at  least  partially,  accomplished  by  the  disintegra- 


FIG.  349. — APEX  OF  AN  INTESTINAL  VILLUS  OF  A 
RABBIT  WHICH  HAD  BEEN  FED  WITH  MILK. 

The  fat  droplets  have  been  blackened  by  fixa- 
tion with  picric  acid  and  osmium  tetroxid.  The 
figure  shows  the  distribution  of  fat  during  certain 
stages  of  absorption.  Alum  carmin  stain.  High- 
ly magnified.  (After  R.  Heidenhain,  from 
Oppel.) 


THE  ALIMENTARY  CANAL  377 

tion  of  fat-laden  leukocytes  which,  by  ameboid  motion,  have  found  their 
way  into  the  lacteal.  Other  fat  particles  may  possibly  find  their  way 
into  the  lacteal  without  the  aid  of  the  leukocytes — a  process  which 
may  be  more  or  less  dependent  upon  the  vital  properties  of  the  lining 
endothelium. 

The  absorption  of  the  products  resulting  from  the  digestion  of 
the  starches,  sugars,  albumins,  etc.,  probably  proceeds  along  similar 
lines.  The  peptones  enter  the  epithelium  in  solution  and  are  then 
secreted,  as  albumins  and  globulins,  into  the  tissue  spaces,  whence  they 
find  their  way  into  the  lacteals  and  capillaries.  Thus  the  lacteals 
become  widely  distended  even  in  the  absence  of  the  digestion  and 
absorption  of  fat. 

THE  LARGE  INTESTINE 

The  large  intestine  includes  the  cecum,  the  colon  (ascending,  trans- 
verse, and  descending  portions)  and  the  rectum.  It  measures  about 
180  centimeters  (5  feet)  in  length,  and  from  3  inches  at  the  beginning 
to  about  ll/2  inches  towards  the  end  of  the  colon.  It  connects  the 
ileum  with  the  anus.  The  vermiform  appendix  represents  an  atrophic 
vestige  of  the  terminal  portion  of  the  embryonic  cecum. 

The  three  outer  coats  of  this  portion  of  the  alimentary  canal  are 
identical  in  structure  with  those  of  the  small  intestine,  with  a  single 
exception  in  the  irregular  distribution  of  the  outer  layer  of  the  mus- 
cular coat,  which  in  the  large  intestine  forms  three  distinct  longitudinal 
bands  or  thickenings,  the  tenice  (linece)  coli.  At  other  parts  of  the 
circumference  of  the  organ  the  outer  muscular  layer  is  slightly  thinner 
than  in  the  small  intestine. 

Since  the  teniaB  are  shorter  than  the  other  coats  of  the  colon,  they 
produce  a  succession  of  sacculations  or  haustra  the  boundaries  of  which 
are  marked  internally  by  crescentic  folds,  involving  the  entire  wall, 
the  plicce  semilunares.  These  sacculations  furnish  conspicuous  external 
marks  by  which  the  large  can  be  differentiated  macroscopically  from 
the  small  intestine.  Another  differential  characteristic  of  the  colon 
is  the  presence  generally  of  fringes  and  bags  of  adipose  tissue  attached 
along  the  median  border  to  the  serosa,  the  appendices  epiploicce. 

The  Mucous  Membrane. — The  mucous  membrane  of  the  large  in- 
testine may  be  best  described  by  comparison  with  that  of  the  small 
intestine.  If  the  mucosa  of  the  latter  organ  be  considered  to  contain 
two  zones,  a  superficial  layer  of  villi  and  a  deeper  glandular  layer,  that 
of  the  large  intestine  may  be  said  to  consist  of  only  the  deeper  of  these 


378 


THE  DIGESTIVE  SYSTEM 


zones.  It  therefore  possesses  no  villi,  and  its  simple  somewhat  longer 
(about  0.5  millimeter)  tubular  glands  extend  from  the  free  surface 
almost  to  the  muscularis  mucosse.  Villi  are  present,  however,  in  the 
embryo,  but  disappear  about  the  sixth  month  (Johnson,  1913). 

The  Lining  Epithelium. —The  lining  epithelium  of  the  large  in- 


01  and 


Tunica 
muscularis 


Tunica 
serosa 

FIG.  350. — TRANSVERSE  SECTION  OF  COLON  OF  DOG. 

The  majority  of  the  glands  are  cut  longitudinally,  some  transversely, 
a  few  obliquely.   X45. 

testine  is  of  the  simple  columnar  variety  and  has  only  an  indistinct  cu- 
ticular  margin.  That  of  the  glands  contains  both  columnar  and  goblet 
cells,  the  latter  being  far  more  numerous  than  in  the  small  intestine. 
The  large  intestine  contains  no  plicae  circulares. 

The  Lymphoid  Tissue.— The  lymphoid  tissue  of  the  large  intestine 
occurs  in  the  corium  in  diffuse  form,  and  as  solitary  nodules,  which 
latter  frequently  break  through  the  muscularis  mucosffi  and  protrude 
into  the  submucosa.  Lymph  nodules  are  especially  abundant  in  the 


THE  ALIMENTARY  CANAL 


379 


rectum  and  in  the  vermiform  appendix.  In  the  latter  the  nodules  are 
more  or  less  confluent,  a  condition  which  is  not  found  elsewhere  in 
the  large  intestine.  In  the  appendix  the  greater  portion  of  the  mucous 
membrane  is  invaded  hy  lymphoid  tissue,  and  the  glands  are  much 
diminished  in  hoth  number  and  size  (Fig.  352). 

The  Vascular  and  Nerve  Supply.— The  vascular  and  nerve  supply 
of  the  large  intestine  is 
identical  in  its  arrangement 
with  that  of  the  small  intes- 
tine. The  mucous  mem- 
brane contains  a  capillary 
plexus  of  blood  and  lym- 
phatic vessels  in  the  corium 
about  the  glands.  The 
nerves  of  the  large  intestine 
include  both  mcdullated  and 
non-medullated  fibers.  The 
latter  supply  its  muscular 
coats  and  blood-vessels.  The 
former  end  in  naked  vari- 
cose or  knobbed  fibrils  be- 
neath and  upon  the  epithe- 
lium of  the  glands.  The 
usual  myenteric  ( Auer- 
bach's)  and  submucous 
(Meissner's)  plexuses  ap- 
pear in  the  large  intestine 

with  the  same  structure  and  location  as  elsewhere  in  the  alimentary 
canal. 

In  the  rectum  the  lining  epithelium  is  continuous  at  the  anus  with 
the  stratified  squamous  epithelium  of  the  skin.  In  this  region  also, 
the  circular  fibers  of  the  inner  layer  of  the  muscular  coat  are  much 
thickened  to  form  the  internal  rectal  sphincter.  Lymphoid  tissue 
abounds  in  the  rectal  mucous  membrane.  The  glands  are  less  numerous 
but  larger  than  in  the  colon  proper,  and  the  mucosa  is  thicker.  In  the 
lower  portion  of  the  rectum  the  mucosa  is  thrown  into  a  number  of 
longitudinal  folds,  the  rectal  columns,  at  which  level  the  columnar 
epithelium  changes  to  stratified  squamous  type. 

The  Ileocecal  (Colic)  Valve. — The  ileocecal  valve,  which  guards 
the  orifice  by  which  the  small  intestine  opens  into  the  large,  is  formed 


FIG.  351. — SECTION  OF  PORTION  OF  LAKGE  INTES- 
TINE OF  DOG,  SHOWING  THE  INTESTINAL 
GLANDS  (CRYPTS  OF  LIEBEBKUHN)  CUT 
ACROSS,  THEIR  LINING  INCLUDING  COLUMNAR 
AND  GOBLET  CELLS. 


380  THE  DIGESTIVE  SYSTEM 

by  a  reduplication  of  the  mucous  membrane,  which  is  strengthened  by 
a  thickening  and  overlapping  of  the  circular  muscular  layers  of  both 
small  and  large  intestines.  The  valve  itself  consists  of  an  upper  and 
lower  segment  enfolding  the  slit-like  orifice;  laterally  the  two  folds  unite 
to  form  the  f  renulum,  which  encircles  the  colon  and  marks  the  boundary 
between  it  and  the  cecum. 

The  outer  longitudinal  muscular  layer  is  continued  directly  from 
the  wall  of  the  ileum  to  that  of  the  cecum,  and  therefore  pursues  a 
relatively  shorter  course  than  either  the  internal  muscular  layer  or  the 
mucous  membrane.  Section  of  only  the  outer  layer  of  the  muscular  coat 


i 


Fro.  352. — TRANSECTION  OP  THE  VERMIFORM  APPENDIX  OP  MAN. 

The  tela  submucosa  contains  three  lymph  nodules  (at  the  right),  two  of  which  have 

pushed  beyond  the  scattered  bundles  of  the  lamina  muscularis  mucosae  into  the 

lamina  propria  of  the  tunica  mucosa,  a  mass  of  diffuse  lymphoid  tissue  (at  the  left), 

and  some  adipose  tissue.  Xll. 

permits  one  to  straighten  the  fold  of  the  intestinal  wall  and  thus  oblit- 
erate the  valve.  In  other  words,  the  outer  muscular  layer  is  not  included 
in  the  valvular  reduplication. 

The  muscularis  mucosce  is  slightly  thickened  at  the  margin  of  the 
valve.  At  this  point  also,  the  villi  become  shorter  and  at  the  margin 
of  the  cecal  surface  of  the  valve  they  entirely  disappear. 

The  following  tabular  statement  of  the  more  important  characteris- 
tics of  the  several  portions  of  the  alimentary  tract  may  be  of  assistance  to 
the  student  in  the  identification  of  raicroscopic  sections  of  these  organs. 


A 

II 


m 

§1 1 


U 

CO  3 


I 


a""1-^ 


11 

3  bC 


ll 


i 


P 

ol 


1~J 

11 


I8 


i§ 


mi- 


Muco- 
nou 
pariet 


ed 


II 


O 
381 


382 


THE  DIGESTIVE  SYSTEM 


THE  SALIVARY  GLANDS 


General  Considerations. — The  salivary  or  oral  glands  include  the 
smaller  glands  of  the  oral  cavity  and  three  pairs  of  large  compound 
tubulo-acinar  glands,  the  parotid,  submaxillary,  and  sublingual  glands. 

The  three  large  pairs  are  commonly 
designated  as  the  salivary  glands 
proper,  the  smaller  as  the  accessory 
salivary  glands.  All  these  are  of  the 
tubulo-acinar  type,  but  certain  ones 
secrete  a  mucous  fluid  while  others  pro- 
duce an  albuminous  secretion  which 
contains  no  mucus.  The  former  are 
known  collectively  as  the  mucous,  the 
latter  as  the  serous  salivary  glands. 
Still  other  salivary  glands  secrete  a 
fluid  which  is  intermediate  in  compo- 
sition, and  as  these  glands  contain  cer- 
tain alveoli  which  resemble  those  of 
the  mucous,  and  others  which  are  sim- 
ilar to  those  of  the  serous  glands,  this 
type  is  known  as  mixed  salivary 
glands. 

The  salivary  glands  may  therefore 
be  subdivided  into: 

I.  Mucous   glands;  glands   on  the 
anterior  surface  of  the  hard  and  soft 
palate  (palatine  glands)  and  the  mu- 
cous glands  of  the  margins  and  root  of 
the  tongue. 

II.  Mixed        glands;        submaxil- 
lary, sublingual,  molar,  buccal,  labial 
and    the   anterior   lingual    glands    (of 
Xuhn). 

III.  Serous  glands;  parotid,  and  von  Ebner's  glands  at  the  base 
of  the  tongue. 

The  form  of  the  salivary  glands  will  be  appreciated  by  examination 
of  the  accompanying  diagram  (Fig.  353)  which  represents  one  of  the 
smaller  glands  of  this  type.  The  larger  ones  are  constructed  in  the 


FIG.  353. — SEMIDIAGRAMMATIC  REP- 
RESENTATION OF  A  SMALL  Mu- 
cous GLAND  FROM  THE  ORAL 
MUCOSA  OF  A  RABBIT. 

a,  mucous  alveoli;  e,  epithelium 
of  the  oral  mucosa;  m,  mouth  of 
the  glandular  duct.  X  70.  (After 
Kolliker.) 


THE  SALIVARY  GLANDS 


383 


same  manner,  the  larger  number  of  their  secreting  alveoli  or  acini  arising 
through  a  more  complex  duct  system. 

The  larger  ducts  of  the  gland  are  lined  by  columnar  cells,  which, 


FIG.  354. — CORROSION  MODEL  OF  AN  INTERLOBULAR  DUCT  AND  ITS  BRANCHES,  FROM 
THE  HUMAN  SUBMAXILLARY  GLAND. 

C,  inter lobular  duct;  D,  large  intralobular  duct;  E,  small  intralobular  duct;  F,  inter- 
calary duct.     X  12.     (After  Flint.) 


as  they  approach  their  termination,  become  superposed  and  thus  offer 
a  gradual  transition  to  the  stratified  squamous  epithelium  upon  whose 
surface  they  open.  The  epithelium  rests  upon  a  basement  membrane 


384  THE  DIGESTIVE  SYSTEM 

which,  in  the  larger  ducts,  is  invested  with  a  fibre-elastic  coat  containing 
a  few  longitudinal  smooth  muscle  fibers. 

The  ducts  divide  and  subdivide  in  an  arborescent  manner,  the  larger 
branches  lying  in  the  connective  tissue  which  invests  the  lobules  into 
which  the  gland  is  subdivided,  while  the  smaller  branches  are  found 
within  the  lobule.  The  duct  system  is  thus  divisible  into  iuterlobular 
and  intralobular  ducts;  the  latter  include  generally  an  excretory  por- 
tion continuous  with  the  interlobular  duct,  a  modified  'salivary'  se- 
cretory portion,  and  a  constricted  intercalary  or  intermediate  portion 
connecting  with  the  acinus. 

In  the  smaller  glands  of  the  mouth  the  number  of  subdivisions 
of  the  duct  system  is  relatively  small,  but  in  the  larger  salivary  glands 
the  small  ducts  are  practically  innumerable.  Thus,  in  the  submaxillary 
gland,  Flint  (Amer.  Jour,  of  Anat.,  1902)  found  that  the  interlobular 
"duct  system  formed  1,500  terminal  branches,  each  of  which  entered 
a  lobule  and  was  further  subdivided  into  intralobular  and  intercalary 
ducts  before  terminating  in  the  secreting  acini.  The  larger  glands 
may  therefore  be  said  to  bear  to  the  smaller  ones  represented  in  Fig. 
353,  a  relation  which  is  comparable  with  that  of  a  full-grown  tree  to  the 
youngest  sapling. 

The  larger  salivary  glands  are  enveloped  by  a  fibro-elastic  capsule 
continuous  with  the  adjacent  areolar  tissue.  From  this  capsule  coarse 
trabecula?  enter  to  divide  the  gland  into  groups  of  lobules,  the  lobes. 
The  lobules  are  invested  by  more  delicate  septa  from  the  interlobar 
trabeculas.  The  ducts  of  the  interlobar  connective  tissue  may  be  desig- 
nated interlobar  ducts  to  distinguish  them  from  the  interlobular  ducts 
between  the  lobules.  These  are  the  excretory  ducts  of  the  system;  the 
'salivary'  intralobular  ducts  have  a  secretory  function.  The  glandular 
tissue  is  known  as  the  parenchyma,  the  connective  tissue -as  the  inter- 
stitial tissue  of  the  gland. 

The  smaller  intralobular  ('salivary*)  ducts  are  lined  by  columnar 
epithelium  whose  cells  contain  two  zones,  one  on  either  side  of  the 
centrally  situated  nucleus.  The  distal  zone  or  free  extremity  of  the 
cell  is  finely  granular,  the  proximal  zone  or  base  presents  a  character- 
istic striated  appearance  which  is  apparently  due  to  a  fibrillar  structure 
of  the  cytoplasm  in  this  portion  of  the  cell.  The  basal  fibrillae  are 
probably,  in  part  at  least,  the  mitochondria  which  are  present  in  all 
functionally  active  cells.  The  epithelium  is  easily  detached  from  its 
basement  membrane  by  the  artificial  contraction  of  the  tissues  during 
fixation  and  hardening. 


THE  SALIVARY  GLANDS 


385 


The  lumen  of  the  ducts  is  of  considerable  diameter  and  contains 
the  reticulated  or  granular  particles  of  the  secretion.  The  larger  ducts 
lie  in  the  connective  tissue  septa  which  invest  the  lobular  groups  of 
acini.  Each  of  these  groups  is  derived  from  the  ramifications  of  the 
terminal  branch  of  an  interlobular  duct  which  enters  the  lobule  to 
divide  into  numerous  intralobular  ducts,  and  secondarily,  through  a 
short  intermediate  or  intercalary  portion,  into  the  secreting  alveoli  or 
acini.  The  intercalary  ducts  are  lined  by 
low  cuboidal  epithelium  and  are  the  smallest 
tubules  of  the  gland.  As  the  duct  passes 
into  the  acinus  the  tubule  is  increased  in 
size,  and  its  secretory  epithelium  becomes 
taller.  The  tubular  acinus  is  more  or  less 
tortuous  and  possesses  a  sacculated  or  alveo- 
lar appearance. 

The  epithelium  differs  accordingly  as  it 
secretes  a  mucous  or  a  serous  fluid.  Thus 
the  acini  are  either  mucous  or  serous  secret- 
ing. 

THE  SEROUS  ACINI. — The  serous  acini 
contain  pyramidal  epithelial  cells  of  sufficient 
height  to  almost  completely  fill  the  tubule; 
hence  the  lumen  is  very  narrow.  The  form 
of  the  secreting  cells  is  somewhat  irregular—  £'  .intercalary  duct;  H;  acini. 

Highly  magnified     (After 
a  tact  which  apparently  depends  upon  their     Flint.) 

crowded  condition  within  the  acinus.     The 

nucleus  is  situated  in  the  central  portion  or  in  the  proximal  end  of 
the  cell,  and  is  spheroidal  in  shape.  The  cytoplasm  is  finely  gran- 
ular, the  granules  being  more  prominent  in  the  distal  portion  of  the 
cell. 

The  epithelium  rests  upon  a  basement  membrane  within  which, 
beneath  the  bases  of  the  secreting  epithelial  cells,  are  certain  flattened 
'basket-cells'  which  here  and  there  send  short  processes  between  the 
cells  of  the  secretory  epithelium  and  thus  provide  cup-like  depressions 
which  receive  the  bases  of  the  secreting  cells.  The  function  and  origin 
of  these  'basket-cells'  is  not  at  present  known.  They  are  readily  recog- 
nized by  their  deeply  stained  and  flattened  nuclei  which  are  contained 
within  the  thin  cytoplasmic  cell  body.  They  may  be  immature  acinal 
cells,  destined  to  replace  worn-out  secretory  cells. 

The   appearance    of    the   secreting   epithelium   varies    with    its   ae- 


FIG.  355. — INTERCALARY 
DUCTS  AND  ACINI  OF 
THE  HUMAN  SUBMAXIL- 
LARY  GLAND,  CORROSION 
MODEL. 

F,  small  intralobular  duct, 


386 


THE  DIGESTIVE  SYSTEM 


tivity.  During  rest  the  granular  secretion  accumulates  within  the  cell, 
until  the  non-granular  zone  is  reduced  to  a  narrow  rim  at  its  basal 
extremity  and  the  nucleus  is  obscured  and  pushed  somewhat  basalward. 
The  cell  becomes  therefore  much  swollen  and  the  alveolar  lumen  almost 
obliterated.  During  activity  the  zymogen  granules  are  discharged  into 
the  lumen;  the  cell  shrinks  and  becomes  clearer;  the  nucleus  appears 
more  distinct,  and  the  granular  zone  becomes  progressively  narrower, 

the  basal  non-granular 
zone  being  correspon- 
dingly increased  in 
breadth.  In  this  basal 
zone  elongated  gran- 
ules have  been  demon- 
strated, which  in  part 
are  to  be  regarded  as 
prozymogen  ('basal 
filaments'  of  Solgcr), 
in  part  (revealed  by 
special  technic)  as 
mitochondria. 

-^Ifi^S11^     ~*  M/'r  The  serous  cells 

^**&K*> f^BMi&a^l*  are  Providcd  with  sys- 

tems of  secretory  ca- 
naliculi which,  begin- 
ning at  the  glandular 
lumen,  invest  the  cell 
w  i  t  h  a  network  of 
canals  which  lie  in  the 
intercellular  substance 

and  may  even  send  short  offshoots  or  intracellular  canaliculi  into  the 
body  of  the  cell  itself.  These  canaliculi  are  considered  to  be  character- 
istic of  the  serous  acini  and  are  not  found  in  relation  with  the  cells  of 
the  mucous  acini  (Fig.  358). 

THE  Mucous  Acrxi. — The  mucous  acini  may  contain  only  mucus- 
secreting  epithelium,  or  they  may  also  include  certain  finely  granular 
acidophil  cells  which  resemble  the  epithelium  of  the  serous  glands.  The 
former  variety  of  acinus  is  found  in  the  mucous  glands  at  the  base 
of  the  tongue  and  in  the  soft  palate;  the  latter  in  the  sublingual  gland, 
in  the  lingual  glands  of  Nuhn,  and  in  the  mucous  glands  of  the  lips 
and  cheeks. 


FIG.  356. — A  GROUP  OF  Mucous  ACINI,  FROM  THE 
HUMAN  SUBMAXILLARY  GLAND. 


a-a,  interlobular  connective  tissue. 
Photo.     X  510. 


Hematein  and 


THE  SALIVARY  GLANDS 


387 


The  serous  appearing  cells  of  the  latter  form  of  mucous  acinus  are 
frequently  arranged  as  crescentic  groups  bordering  upon  the  adjacent 
mucous  cells.  Such  groups  are  known  as  the  demilunes  (of  Heidenhain) 
or  crescents  (of  Gianuzzi;  Fig.  357).  They  occur  at  the  periphery 
of  the  acinus,  their  base  being  applied  to  the  membrana  propria,  their 
inner  margin  sometimes  reaching  the  glandular  lumen,  but  more  fre- 
quently separated  therefrom  by  the  overlapping  of  the  adjacent  niu- 


Fio.  357. — FROM  THE  SUBLINGUAL  GLAND  OF  MAN. 

a,  salivary  intralobular  duct;  e,  acinus  whose  cells  contain  no  mucus;  s,  mucous 
acini,  at  s'  with  a  demilune;  sz,  mucous  cells  in  the  duct.  X  500.  (After  Kolli- 
ker.) 


cous  cells.  The  demilunes  are  frequently  found  at  the  blind  ex- 
tremity of  the  secreting  acinus,  but  they  may  also  occur  along  its 
sides. 

The  nature  of  the  demilunes  is  the  subject  of  considerable  discussion. 
ITeidenham  (Arch.  mikr.  Anat.,  18G9)  first  advanced  the  theory  that 
the  mucous  cells  were  destroyed  during  secretion,  and  thqt  the  function 
of  the  demilunes  was  therefore  to  replace  the  disintegrated  mucinous 
cells.  This  theory  has  been  practically  abandoned,  for  no  one  has  yet 
demonstrated  active  cell  division  in  the  demilunes,  a  process  which 
would  necessarily  be  concomitant  with  the  rapid  development  of  mucus 
from  demilune  cells. 

Hebold  (1879)   is  responsible  for  the  theory,  strongly  supported  by 


388 


THE  DIGESTIVE  SYSTEM 


Stb'hr,  that  the  demilunes  represent  an  inactive,  the  mucous  cells,  an 
active  phase  of  mucus  secretion.  The  easy  demonstration  of  inter- 
mediate stages  in  many  mucus-secreting  glands  lends  strong  support  to 
this  theory,  and  in  the  present  state  of  our  knowledge  it  seems  beyond 
doubt  that  such  a  process  actually  occurs  in  at  least  some  of  the  mucus- 
secreting  glands. 

A  third  theory,  more  recently  advanced  by  Solger  (Anat.  Anz.,  1894) 
and  stoutly  supported  by  Krause  (Arch.  mikr.  Anat,  1895,  1897,  and 
1901)  and  others,  considers  the  demilunes  to  be 
true  secreting  cells  which  form  a  serous  secre- 
tion and  are  therefore  functionally  independent 
of  the  mucinous  cells.  This  theory  receives 
strong  confirmation  in  the  fact  first  observed 
by  Cajal  (1889)  and  since  that  time  repeatedly 
demonstrated,  that  the  demilunes,  like  the  true 
serous  cells,  are  provided  with  a  system  of  in- 
tercellular secretory  canaliculi  by  which  they 
are  placed  in  relation  with  the  glandular  lumen. 
Moreover  Krause  was  able  to  demonstrate  that 
granules  of  sodium  indigo  sulphate  were  se- 
creted by  these  cells,  as  also  by  the  true  serous 
cells  and  the  striated  epithelium  of  the  intra- 
lobular  ducts. 

The  mucus-secreting  cells  examined  in  the 
fresh  state  present  a  clear,  highly  refractive 
appearance.  They  closely  resemble  the  typical 
goblet  cells,  but  instead  of  being  isolated  among 
the  granular  serous  cells,  they  may  invest  the 
entire  acinus,  or  even  the  whole  of  a  small 
lobule  may  contain  only  mucus-secreting  cells. 

After  the  customary  preparation  by  fixation  and  staining,  the  mu- 
cous cells  present  a  coarse  basophilic  reticulum  which  occupies  the  distal 
portion  of  the  cell.  Coarse  granules,  with  proper  fixation  and  in  fresh 
tissue  as  well,  can  be  demonstrated  within  the  meshes  of  the  reticu- 
lum. These  granules  are  readily  colored  by  the  so-called  specific  mu- 
cus stains  (Mayer's  muehematein  and  mucicarmin,  safranin,  and  thio- 
nin). 

In  the  mucous  cells  the  nucleus  is  crowded  to  the  base  or  proximal 
end  of  the  cell  and  flattened  against  the  basement  membrane.  It  is  sur- 
rounded by  a  small  remnant  of  finely  granular  cytoplasm,  which,  after 


FIG.  358. — Mucous  ACINI 
OF  THE  RETROLINGUAL, 
GLAND  OF  THE  RAT. 

The  ducts  and  secretory 
capillaries  have  been  black- 
ened, r,  demilunes  with 
secretory  capillaries;  s, 
mucous  cells.  Golgi  meth- 
od. X500.  (After  K61U- 
ker.) 


•^Zj;." 

FIG.  359. — DIAGRAM  OF  THE  ARRANGEMENT  OF  THE  CELLS  IN  A  MIXED  SALIVARY 

GLAND. 

a,  intralobular  duct;  a',  intercalary  duct;  b,  serous-secreting  tubules;  c,  muc::s- 
secreting  tubules;  d,  demilune.     (After  Krause.) 


CD 

FIG.  360. — DIAGRAMS  OF  A,  PAROTID  GLAND;  B,  SUBMAXILLARY  GLAND;  C,  SUB- 
LINGUAL  GLAND;  AND  D,  PANCREAS.     (After  Sobotta.) 

«i,  interlobular  duct;  a2,  intralobular  duct;  sr,  salivary  intralobular  d''<jt;  s,  inter- 
calary duct;  hm,  demilune;  ts,  serous  alveolus;  tm,  mucous  alveolus 


390 


THE  DIGESTIVE  SYSTEM 


the  discharge  of  the  mucus  during  secretion,  is  presumably  capable  of 
reloading  the  cell  with  its  mutinous  content. 

We  will  now  consider  the  more  important  peculiarities  of  each  of 
the  larger  salivary  glands. 

The  Parotid  Gland. — This  is  the  largest  of  the  salivary  glands  and 
in  man,  sheep,  dog,  cat  and  rabbit  is  purely  a  serous-secreting  organ. 
However,  in  sheep,  dog  and  cat  it  contains  also  a  variable  number  of 

mucous  alveoli  during 
the  first  year ;  these  de- 
generate arid  entirely 
disappear  during  the 
second  year  (Brock  and 
Trautmann,  Anat.  Anz., 
47,  17,  1914). 

It  is  situated  in 
front  of  the  external 
ear,  and  overlaps  in- 
feriorly  both  faces  of 
the  upper  portion  of  thj 
ramus  of  the  mandible. 
A  variable  number  of 
small  accessory  lobules, 
including  mucus-pro- 
ducing alveoli,  lie  along 
the  course  of  the  main 
parotid  (Stensou's) 
duct.  The  latter  opens  into  the  mouth  at  the  level  of  the  second  upper 
molar.  The  parotid  is  invested  by  a  dense  fibre-elastic  sheath,  septa  from 
which  divide  the  gland  into  lobes  and  lobules.  The  lobes  and  lobules  are 
firmly  united  by  the  dense  but  narrow  bands  of  connective  tissue;  these 
contain  the  larger  ducts,  blood-vessels,  lymphatics,  and  a  few  small  gan- 
glia. 

The  secreting  acini  are  relatively  long  and  tortuous;  they  are  fre- 
quently branched  or  forked.  Because  of  the  Telatively  low  height  of 
their  serous-secreting  cells  the  acini  appear  slender  and  their  lumen  is 
irregular,  indistinct,  and  very  narrow.  The  'basket  cells'  upon  which  the 
secreting  cells  rest  are  highly  developed  in  the  parotid  and  often  form 
a  complete  investment  for  the  acinus.  , 

The  acini  of  the  parotid  are  all  of  one  type.  The  only  other  tubules 
within  the  lobules  of  this  gland  are  the  intercalary  and  the  intralobular 


FIG.  361. — FROM  A  SECTION  OF  THE  HUMAN  PAROTID 
GLAND. 

I,  lumen  of  a  serous  acinus;  sch,  intercalary  duct; 
sr,  intralobular  duct;  T,  secreting  acini.  Hematoxy- 
lin  and  eosin.  X  280.  (After  Sobotta.) 


THE  SALIVARY  GLANDS 


391 


or  salivary  ducts.  The  former  are  characterized  by  their  very  narrow 
caliber  and  low  epithelium.  They  are  slender  tubules  which  open  on  the 
one  side  from  the  acini  and  on  the  other  into  the  branched  terminals  of 
the  more  spacious  salivary  ducts.  The  'salivary*  (secretory)  portion  of 
the  intralobular  duct  has  a  somewhat  greater  diameter  also  than  the 
excretory  portion,  which  is  histologically  similar  to  the  interlobular 
ducts.  In  the  parotid  the  salivary  ducts  are  relatively  short  as  com- 
pared with  the  intermediate  ducts,  but  are  readily  recognized  by  their 
striated  columnar  epithelium, 
which  is  deeply  colored  by  acid 
dyes  (eosin,  etc.),  and  are  thus 
sharply  distinguished  from  the 
secreting  cells  of  the  acini, 
which  stain  poorly  with  these 
dyes. 

The  Submaxillary  Gland. 
— In  man  and  in  most  mam- 
mals this  organ  is  a  mixed  sal- 
ivary gland;  that  of  the  bear 
and  dog  contains  the  largest, 
that  of  man  and  the  apes  the 
smallest  proportion  of  mucous 

acini     (Krause,    Arch.    mikr. 

FIG.  362. — FROM  A  SECTION  OF  THE  HUMAN 

A  nat.,    1897).      In    man    the  SUBMAXILLARY  GLAND. 

proportion  of  mucous  to  serous 
alveoli    is    about    one    to    five 
(Piersol).      The   submaxillary 
is  situated  in  the  floor  of  the 
mouth  under  the  posterior  por- 
tion of  the  mandible.    The  main  submaxillary  (Wharton's)  duct  opens 
into  the  mouth  one  on  either  side  of  the  frenulum  of  the  tongue,  some- 
times joined  by  the  duct  of  the  sublingual  gland. 

The  serous  acini  of  the-  submaxillary  are  shorter  and  less  typically 
tubular  than  those  of  the  parotid,  and  they  are  lined  by  taller  secreting 
cells.  The  diameter  of  the  acinus  is  therefore  slightly  greater  in  this 
gland  than  in  the  parotid.  Its  mucous  acini  contain  a  relatively  large 
proportion  of  demilunes. 

The  intercalary  ducts  are  considerably  shorter  than  in  the  parotid, 
while  the  salivary  intralobular  ducts  are  much  longor  in  the  submaxil- 
lary. The  interlobular  connective  tissue  is  not  quite  so  delicate  as  in 


In  the  center  is  a  small  salivary  duct,  just 
above  which  are  three  mucous  acini,  the 
uppermost  one  possessing  a  demilune.  The 
other  acini  are  serous.  Hematein  and  eosin. 
Photo.  X  370. 


392 


THE  DIGESTIVE  SYSTEM 


the  parotid.  It  contains  many  sympathetic  ganglia  of  relatively  large 
size.  Small  lamellar  corpuscles  of  simple  construction  are  occasionally 
found  in  the  interlobular  connective  tissue  (Krause). 

The  Sublingual  Gland.— This  is  the  smallest  of  the  three  pairs  of 
large  salivary  glands.  It  is  not  invested  by  a  distinct  capsule.  It  lies 
under  the  floor  of  the  mouth  anteriorly,  one  on  either  side  of  the  frenu- 
lum.  It  is  a  mixed  gland  in  man,  dog,  cat  and 
rabbit.  It  differs  from  the  submaxillary,  how- 
ever, in  that  all  of  its  acini  are  mucous.  It  be- 
comes 'mixed'  by  reason  of  the  presence  of  very 
many  demilunes  (serous  cells).  Although  iso- 
lated sections  which  pass  through  the  larger 
collections  of  demilune  cells  may  appear  as  sec- 
tions of  serous-secreting  tubules,  if  examined 
in  longitudinal  section  or  by  reconstruction  the 
true  mucous  character  of  each  lobule  is  ap- 
parent. Many  of  the  terminal  acini  of  the 
sublingual  gland,  however,  although  much 
branched,  contain  no  demilunes.  The  'basket 
cells'  are  readily  recognized  in  the  acini  of  this 
gland  though  they  are  less  highly  developed 
here  than  in  the  parotid.  Its  intralobular  duct 
system  lacks  intermediate  ducts,  and  is  largely 
of  the  'salivary'  type. 

Accompanying  the  sublingual  gland  proper,- 
or  larger  component,  are  a  variable  number  (5 
to  20)  of  accessory  sublingual  glands  of  various 
sizes.  They  consist  largely  of  mucous  alveoli,  each 

gland  opening  into  the  mouth  by  an  independent  duct.  The  duct  of  the 
sublingual  proper  (duct  of  Bartholin)  opens  at  the  side  of  the  frenulum. 
Blood  Supply. — The  salivary  glands  possess  a  rich  blood  supply. 
The  arteries  accompany  the  glandular  ducts  within  the  interlobar  and 
interlobular  connective  tissue,  and  thus  reach  all  the'  lobules  of  the 
gland.  Small  arterial  twigs  enter  the  lobule  from  all  sides  and  form  a 
rich  capillary  plexus  in  the  delicate  connective  tissue  coats  of  the  acini. 
The  capillaries  are  thus  brought  into  intimate  relation  with  the  secreting 
cells,  from  which  they  are  only  separated  by  the  basement  membrane  of 
the  acinus.  The  veins  return  by  a  similar  course,  the  smallest  venules 
passing  out  of  th^  lobule  into  the  connective  tissue  septa  in  which  they 
retrace  the  course  of  the  arteries. 


Fia.  363.— RECONSTRUC- 
TION MODEL  OF  THE 
SUBLINGUAL  GLAND  OF 

MAN. 

An  intralobular  duct 
terminating  in  salivary 
ducts  and  acini.  X  285. 
(After  Maziarski.) 


THE  SALIVARY  GLANES 


393 


Lymphatics. — Lymphatics  are  relatively  few  and  are  for  the  most 
part  confined  to  the  interlobular  septa,  where  they  form  cleft-like  spaces 
which  lead  to  true  lymphatic  vessels  and  so  on  to  the  lymph  nodes  of  the 
cervical  region. 

Nerve  Supply. — The  salivary  glands  are  abundantly  supplied  with 
nerves,  which  are  derived  from  both  sympathetic  and  cerebral  trunks. 
They  are  distributed  to  the  walls  of  the  blood-vessels  and  ducts,  and 
to  the  secreting  cells  of  the  acini.  The  nerve  trunks  are  found  in  the 
interlobular  connective  tissue  where 
they  are  supplied  with  small  ganglia 
which  are  most  abundant  in  the  sub- 
maxillary  and  least  numerous  in  the 
parotid  gland. 

The  sympathetic  fibers  which  inner- 
vate the  blood-vessels  proceed  from  the 
superior  cervical  ganglion.  They  are 
believed  to  be  vasodilator  fibers.  The 
cerebral  nerves,  which  supply  fibers  to 
the  gland  cells,  are  the  facial  and  the 
glossopharyngeal.  The  parotid  gland 
is  supplied  by  the  glossopharyngeal ; 
the  fibers  (secretory  and  vasoconstric- 
tor) passing  by  way  of  the  tympanic 

nerve  (nerve  of  Jacobson),  small  superficial  petrosal,  otic  (sympathetic) 
ganglion,  and  the  auriculotemporal  branch  of  the  inferior  maxillary 
division  of  the  trigeminal  nerve.  The  submaxillary  and  sublingual 
glands  receive  their  secretory  fibers  and  vasoconstrictor  fibers  from  the 
trigeminal  nerve,  by  way  of  the  chorda  tympani  nerve  and  the  submaxil- 
lary (sympathetic)  ganglion.  The  fibers  beyond  the  otic  and  submaxil- 
lary ganglia  are  believed  to  be  true  postganglionic  fibers;  that  is,  axons 
of  cell  bodies  situated  in  these  ganglia.  Sensory  fibers  are  said  to  pass 
to  the  ducts. 

Delicate  fiber  bundles  from  the  interlobular  nerve  trunks  enter  the 
lobules  and  form  a  plexus  of  naked  fibrils  about  the  walls  of  the  acini, 
known  as  the  epilemmal  plexus,  from  which  terminal  fibrils  pierce  the 
basement  membrane  and  as  hypolemmal  fibers  end  in  contact  with  and 
between  the  secreting  cells.  Small  terminal  expansions,  varicosities,  or 
end  knobs  are  found  in  the  course  of  the  hypolemmal  fibers. 


FIG.   364.— NERVE  ENDINGS  IN  A 
SALIVARY  GLAND. 

H,  demilune;  I,  secreting  acini; 
n,  nerve  fibrils.  Highly  magnified. 
(After  Retzius,  from  Rauber.) 


394 


THE  DIGESTIVE  SYSTEM 


THE   PANCREAS 

The  pancreas  is  a  flat  elongate  body  lying  behind  the  stomach  be- 
tween the  loop  of  the  duodenum  and  the  spleen.  It  arises  as  two  anlages : 
a  smaller  from  the  common  bile  duct  (ventral  pancreas),  and  a  larger 
from  the  duodenum  (dorsal  pancreas).  These  subsequently  fuse  to  form 
a  single  organ  drained  mainly  by  the  duct  of  the  ventral  component, 
which  has  meanwhile  made  an  anastomosis  with  that  of  the  dorsal  com- 
ponent, the  latter  proximal  -to  the  anastomosis  nevertheless  commonly 


FIG.  365. — EARLY  STAGES  IN  THE  DEVELOPMENT  OF  THE  PANCREAS,  ILLUSTRATING 
CONDITIONS  IN  THE  5  AND  7  WEEKS  OLD  HUMAN  EMBRYOS. 

Dp,  dorsal  pancreas;  Vp,  ventral  pancreas;  Pd,  pancreatic  (Wirsung's)  duct; 
Apd,  accessory  pancreatic  (Santorini's)  duct;  Dch,  ductus  choledochus;  cd,  cystic 
duct;  Hd,  hepatic  duct.  (Adapted  from  Kollman.) 


remaining  pervious  and  functional.  The  pancreas  bears  a  close  struc- 
tural resemblance  to  the  salivary  glands,  more  especially  the  parotid. 
It  is  a  compound  tubulo-acinar  gland  which  contains  an  immense  num- 
ber of  small  lobules  associated  into  lobes  and  which  pours  its  secretion 
into  the  lumen  of  the  duodenum  by  means  of  the  chief  (Wirsung's) 
and  accessory  (Santorini's)  pancreatic  ducts.  The  lobules  are  united  by 
a  delicate  and  relatively  very  loose  fibro-elastic  connective  tissue. 

The  ducts  of  the  pancreas  branch  and  arborize  in  the  same  manner  as 
those  of  the  salivary  glands.  The  interlobular  ducts  are  lined  by  a 
single  layer  of  columnar  cells;  in  the  larger  divisions  (interlobar  ducts) 
occasional  goblet  cells  are  found.  The  wall  of  the  interlobular  pan- 
creatic ducts  is  much  thicker  than  in  those  of  the  salivary  glands,  for 


THE  PANCRKAS 


395 


they  possess  a  much  thicker  connective  tissue  coat,  in  which  are  also 
many  longitudinal  smooth  muscle  fibers. 

On  entering  the  lobule  the  duct  is  immediately  transformed  into 


FIG.  366. — FROM  A  SECTION  OF  THE  HUMAN  PANCREAS,  SHOWING  SEVERAL  LOBULES 
AND  THE  BROAD  INTERLOBULAR  BANDS  OF  CONNECTIVE  TISSUE. 

o,  blood-vessel;  b,  pancreatic  islet;  c,  intralobular  duct;  d,  interlobular  duct  and 
accompanying  artery.    Hematein  and  eosin.    Photo.     X  45. 

the  intercalary  (intermediate;  junctional)  type;  in  the  pancreas  there 
are  no  specialized  intralobular  ducts  lined  by  columnar  striated  epithe- 
lium as  in  the  salivary  glands.  The  intercalary  ducts  are  very  slender 
tubules  which  are  lined  by  low  columnar  or  flattened  epithelium.  Be- 
cause of  the  absence  of  larger  intralobular  ducts  the  intercalary  portions 
are  relatively  very  long  and  much  branched* 


396 


THE  DIGESTIVE  SYSTEM 


On  approaching  its  termination  the  lining  cells  of  an  intercalary 
duct  are  still  more  flattened  and  often  acquire  a  considerable  breadth. 
They  are  elongated  in  the  direction  of  the  long  axis  of  the  tubule,  and  in 
surface  view  have  an  irregularly  polygonal  outline  (Bensley).  They 
pass  into  the  acini  in  a  peculiar  manner.  Instead  of  offering  a  direct 


FIG.  367. — DRAWING  OF  AN  INTERCAL- 
ARY DUCT  OF  CAT,  WITH  THREE 
BRANCHES  ENDING  IN  ACINI  TO 
FORM  CENTRO-ACINAL  CELL  GROUPS. 

The  acinar  cells  contain  numerous 
basal  filaments.     X  750. 


FIG.  368. — RECONSTRUCTION 
MODEL  OF  THE  HUMAN 
PANCREAS. 

The  intralobular  duct  gives 
off  long  intercalary  ducts, 
which,  after  branching,  end 
in  the  acini.  X  344.  (After 
Maziarski.) 


transition  from  the  duct  epithelium  to  that  of  the  acinus  the  cells  of 
the  former  frequently  appear  as  if  telescoped  into  the  lumen  of  the 
acinus.  Thus  the  centro-acinal  cells  (of  Langerhans)  are  produced, 
and  consequently  the  centro-acinal  cells  correspond  closely  in  appearance 
with  those  of  the  intercalated  ducts.  They  seem  to  occupy  the  lumen 
of  the  acinus,  and  are  only  separated  from  the  distal  ends  of  the  acinal 
cells  by^the  secretory  capillaries  which  place  the  secreting  cells  in  com- 
munication with  the  lumen  of  the  duct.  The  centro-acinal  cells  are 
characteristic  of  the  pancreatic  acini. 

The  Acini. — The  acini  of  the  pancreas  possess  an  irregular  tubular 
form  with  frequent  alveolar  dilatations.     Their  lining  epithelium  rests 


THE  PANCREAS 


397 


upon  a  reticular  basement  membrane  within  which  are  thin  ^basket 
cells.'  A  delicate  connective  tissue  stroma  invests  the  acini  or  alveoli. 
The  secreting  cells  are  tall  and  irregularly  columnar  or  pyramidal 
in  shape.  Their  nucleus  lies  in  the  proximal  third  of  the  cell  and  is 
surrounded  by  reticular  or  very  finely  granular  cytoplasm.  The  cyto- 


FIG.  369. — ACINI  OF  THE  HUMAN  PANCREAS. 

The  acinus  at  a  is  connected  with  an  intercalary  duct,  cut  in  tangential  section, 
and  occupying  the  center  of  the  figure.    Hematein  and  eosin.    Photo.     X  050. 


plasm  of  the  inner  zone  of  the  cell,  on  the  other  hand,  is  filled  with 
coarse  zymogen  granules  whose  number  is  dependent  upon  the  activity 
of  the  gland.  During  fasting  the  granules  accumulate  until  eventually 
they  almost  completely  fill  the  cell,  but  during  digestion  they  disappear 
with  the  discharge  <>f  the  secretion,  the  width  of  the  granular  zone 
gradually  decreasing,  that  of  the  non-granular  fibrillar  basal  zone  being 
correspondingly  enlarged  (Figs.  371,  A  and  B). 


398 


THE  DIGESTIVE  SYSTEM 


With  the  increased  breadth  of  the  basal  zone  during  secretion,  there 
appears  in  this  portion  of  the  cell  a  structure  which  has  been  de- 
scribed by  Nussbaum  (Arch.  mikr.  Anat.,  1885)  as  the  Nebenkern, 
and  which  has  been  carefully  studied  by  Mathews  (Jour,  of  Morph., 
1899).  This  is  a  spheroidal  basophil  body  which  lies  near  the  nucleus 
and  is  frequently  surrounded  by  a  clear  area  of  cytoplasm.  Its  origin 

and  function  are  undetermined 
and  it  is  possible  that  several 
distinct  bodies  have  been  in- 
cluded under  the  name.  Ogata 
(Arch.  f.  PhysioL,  1883)  con- 
siders that  it  is  derived  from 
the  nucleus  by  the  extrusion 
of  its  plasmosome,  an  opinion 
which  seems  to  be  shared  by  von 
Ebner  (Kolliker's  Handbuch, 
1902,  Ed.  iii,  5,  250).  The 
studies  of  Mathews  have  shown 
that  at  least  in  certain  instances 

FIG.  370.-PANCREATIC    ACINUS    OF   CAT     ifc  is  distinctly  fibrillar  and  sug- 
CUT     TRANSVERSELY     NEAR     FUNDUS,     gest  that   it  may  be  concerned 


SHOWING     THE     BASAL     (PROZYMOGEN) 
FILAMENTS  OF  THE  CELLS. 


with    the   mechanism   of   secre- 
tion.    It  most  probably  repre- 


The   alveoli   of   the   central   portions   of 
the    cells    represent     dissolved     zymogen     sents   a   post-secretion    remnant 


granules.     X   1500. 


basal     fila- 


of     ergastoplasmic 

ments. 

In  addition  to  this  fibrillar  complex  of  basophilous  substance,  there 
may  be  seen  in  •  appropriately  fixed  and  stained  preparations,  another 
group  of  fibrils,  the  mitochondria.  These  can  be  seen  in  fresh  acinar 
cells  and  in  tissue  preserved  in  fluids  which  lack  acids  (mitochondria  are 
dissolved  by  acids),  when  they  also  give  to  the  basal  portion  of  these 
cells  a  striated  appearance.  These  basal  bodies  have  been  extensively 
studied  by  Bensley  (Amer.  Jour.  Anat.,  12,  3,  1911)  in  the  pancreas  of 
the  guinea  pig,  and  their  independence  from  the  basal  filaments  of 
Solger  established.  Mislawsky  also  (Arch.  mikr.  Anat.,  81,  4,  1913) 
has  recently  studied  the  mitochondria  in  the  acinar  cells  of  the  rabbit's 
pancreas.  He  finds  no  evidence  to  indicate  that  they  segment  into  the 
zymogenic  granules.  They  are  described  as  interstitial  elements  of  the 
protoplasmic  reticulum,  more  probably  connected  with  the  general  cell 
metabolism.  There  is  apparently  no  good  evidence  in  support  of  the 


THE  PANCREAS 


390 


FIG.  371. — CELLS  FROM  PANCREAS  OF  NECTURUS. 

A,  after  rest,  and  filled  with  zymogen  granules;  B,  after  activity,  showing  the 
presecretion  (basal;  ergastoplasmic)  filaments,  and  the  so-called  nebenkern  (N). 
(After  Mathews.) 

idea  that  either  the  basal  filaments  of  Solger  or  the  mitochondria  give 
origin  to  secretory  granules,  by  a  process  of  segmentation. 

Pancreatic  Islets.— The  lobules  of  the  pancreas  contain,  in  addi- 
tion to  the  acini  and  ducts,  certain  larger  and  smaller  spheroidal  col- 
lections of  polyhedral  cells  which  lie  in  the  inter-acinar  connective  tissue, 
the  pancreatic  islets  (islands  of  Langerhans;  intralobular  or  interalveolar 


Fia.  372. — Two  ADJACENT  ACINI  FROM  THE  GUINEA-PIG'S  PANCREAS. 

The  one  at  the  right  shows  an  entering  intercalary  duct  and  two  centro-acinal 
cells.  The  acinar  cells  are  filled  proximally  with  a  basophilous  substance  (basal 
filaments),  and  contain  distally  numerous  alveoli,  the  representatives  of  dissolved 
zymogen  granules.  X  1200  (After  Bensley-,  Am.  Jour.  Anat.,  12,  3,  1911.) 


400 


THE  DIGESTIVE  SYSTEM 


FIG.  373. — SECTION  OF  AN  ACINUS  FROM  THE  GUINEA-PIG'S  PANCREAS,  SHOWING  THE 
BASAL  MITOCHONDRIAL  CONTENT  AND  THE  CENTRAL  ZYMOGEN  GRANULES. 

Bensley's  mitochondrial  technic.    X  1200  (After  Bensley,  Am.  Jour.  Anat.,  12,  3, 
1911.) 

cell  groups).  The  islet  cells  are  arranged  in  irregular  cords,  frequently 
only  two  cells  deep,  lying  in  the  meshes  of  capilliform  sinusoids,  from 
which  they  appear  to  be  separated  by  little  more  than  the  eudothelial 


FIG.  374. — INTERCALARY  DUCT  WITH  BRANCHES,  FROM  PANCREAS  OF  GUINEA-PIG, 
SHOWING  HIGHLY  BRANCHED  TUBULES  CONNECTED  WITH  THE  DUCT  AND  WITH 
AN  ISLET. 

Intravitam  staining  with  pyronin  and  neutral  red.     X    50.     (Bensley,    Amer. 
Jour.  Anat.,  12,  3,  1911.) 

wall.  The  cells  are  divisible  into  two  distinct,  apparently  independent 
types,  on  the  basis  of  their  granular  content  (Lane,  Amer.  Jour.  Anat., 
7,  3,  1907).  The  'A'  and  'W  granules  differ  morphologically  and  micro- 


THE  PANCREAS 


401 


chemically;  it  is  suggested  that  they  indicate  a  twofold  secretion  (Lane). 
The  granules  of  the  islet  cells  of  both  types  differ  markedly  also  from 
those  of  the  acinar  cells.  The  islets  are  of  various  sizes,  ranging  from 
those  with  only  a  few  or  even  a  single  cell  to  those  with  many  cells 
(3  millimeters  in  diameter).  The  number  of  islets  also  varies  greatly  in 
different  individuals.  Thus  De  Witt  (Jour.  Exp.  Med.,  vol.  8,  1906) 
estimated  the  amount  of  islet  tissue  in  three  apparently  normal  subjects 


FIG.  375. — PANCREATIC  ISLET  OF  CAT. 
E,  endothelial  cell;  cap,  capillary;  be,  red  blood  corpuscle.     X  750. 

at  1-25,  1-50  and  1-125  of  the  total  volume  of  the  pancreas.  By  means 
of  intravitam  stains  (neutral  red  and  janus  green),  Bensley  succeeded  in 
staining  differentially  the  islets  of  the  guinea  pig's  pancreas.  He 
counted  from  13,000  to  56,000  in  different  specimens.  Clark  (Anat. 
Anz.,  43,  3,  1913)  employed  this  method  in  a  study  of  human  pancreases 
secured  shortly  after  death,  and  estimates  the  average  number  of  islets 
at  12  per  milligram.  In  one  male  subject  of  24  years  and  140  pounds 
weight,  he  estimated  the  total  number  of  islets  at  1,760,000 ;  in  another 
of  29  years  and  135  pounds  weight,  only  662, 166.  ,0pie  (Johns  Hopkins 
Hosp.  Bull.,  1900)  first  observed  that  the  islets  were  more  abundant  in 
the  tail  and  least  abundant  in  the  head  of  the  pancreas;  this  observation 
is  confirmed  by  both  Clark  and  Bensley.  Laguesse  (Jour,  de  Physiol.  et 


402 


THE  DIGESTIVE  SYSTEM 


de  Path.,  13.,  1,  1911)  described  the  islets  in  continuity  with  the  ducts 
of  the  acini.  Such  continuity  is  described  also  by  Bensley  for  many  of 
the  islets  in  the  guinea  pig's  pancreas.  Bensley's  studies  have  disclosed 
these  further  points  of  relationship  between  the  islets  and  the  zymo- 


FIG.  376.— FROM  THE  HUMAN  PANCREAS.         , 

a,  acini;  b,  is  placed  above  an  interlobular  duct;  c,  a  pancreatic  islet;  a  second 
islet,  circular  in  outline,  lies  near  the  center  of  the  figure.  Hematcin  and  eosin. 
Photo.  X  330. 

genous  parenchyma:  Islets  may  be  located  (1)  in  the  interlobular  con- 
nective tissue,  but  connected  with  the  duct  system;  (2)  in  the  lobules, 
also  unconnected  with  the  acini  (encapsulated),  but  directly  connected 
with  the  interlobular  duct  system;  (3)  in  the  lobules — these  include 
the  great  majority — and  in  connection  with  either  acini  or  ducts  or  both ; 
and  (4)  islets  unconnected  with  either  ducts  or  acini,  both  in  the  inter- 
lobular connective  tissue  and  in  the  acinar  parenchyma. 


THE  PANCEEAS  403 

The  tubules  (intercalary  ducts)  are  said  to  branch  and  anastomose 
freely  and  to  be  capable  of  differentiating  either  into  acini,  or  islets,  or 
both.  They  may  produce  also  small  mucous  glands  which  open  into  the 
tubules ;  and  single  islet  cells  may  be  formed  along  the  ducts.  Notwith- 
standing their  intimate  developmental  relationship  the  islets  remain 
isolated  from  the  general  exocrin  parenchyma,  since  the  lumen  of  the 
connecting  tubules  does  not  penetrate  its  substance.  There  is  no  satis- 
factory evidence  to  show  that  islet  tissue  may  be  increased  or  diminished, 
or  that  acinus  tissue  may  change  into  islet  tissue,  or  vice  versa,  concom- 
itant with  experimentally  induced  alterations  in  nutritive  and  func- 
tional conditions,  as  has  been  repeatedly  claimed ;  nor  is  there  evidence  of 
a  transition  between  islet  and  acinar  cells.  Islets  and  acini  have  a  com- 
mon embryonic  origin,  but  once  differentiated  they  are  not  capable  of 
transformation  one  into  the  other  (Bensley).  The  islets  appear  in  the 
human  pancreas  about  the  time  the  embryo  attains  a  length  of  50  milli- 
meters (Lewis). 

The  islets  are  believed  to  constitute  a  group  of  internally  secreting 
organs.  The  evidence  for  such  conclusion  is  derived  from  a  series  of 
experiments  by  Opie  and  many  others.  When  the  pancreas  is  removed, 
a  form  of  diabetes  follows,  characterized  by  the  appearance  of  sugar  in 
the  urine.  When  the  pancreatic  duct  is  simply  ligated,  the  flow  of  pan- 
creatic juice  is  checked  and  atrophy  of  the  acinar  tissue  ensues,  but  no 
disturbance  in  carbohydrate  metabolism  results,  nor  is  any  alteration 
produced  in  the  islet  tissue.  Moreover,  in  cases  of  death  following 
diabetes  mellitus,  Opie  demonstrated  gross  degenerative  changes.  Ho- 
mans'  recent  experiments  (Jour.  Med.  Eesearch,  March,  1914)  have  ex- 
tended the  evidence  in  support  of  the  conclusion  that  the  islets  are  con- 
cerned in  the  metabolism  of  sugar.  When  more  than  three-fourths  of 
the  pancreas  was  removed  in  cats,  the  main  duct  being  left  intact,  fatal 
diabetes  occasionally  followed.  Microscopic  examination  of  the  islets 
revealed  the  following  conditions :  ( 1 )  in  those  instances  where  diabetes 
did  not  follow  the  operation,  the  islet  cells  showed  signs  of  over-activity 
indicated  in  part  by  a  disappearance  of  secretory  granules;  (2)  in  the 
subjects  which  died  from  diabetes  following  the  operation,  the  islet  cells 
showed  degenerative  changes,  the  acinous  tissue  having  remained  un- 
altered. 

Blood  Supply. — The  large  blood-vessels  of  the  pancreas  accompany 

the  interlobular  ducts,  but  after  repeated  subdivision  these  vessels  part 

company,  and  the  smaller  arteries  pursue  a  separate  course  through  the 

interlobular  connective  tissue.     Thus  they  reach  all  portions   of  the 

20 


404 


THE  DIGESTIVE  SYSTEM 


gland  and  supply  capillaries  to  the  intralobular  connective  tissue  about 
the  acini.  Certain  arterial  branches  also  enter  the  islets  and  form  a 
specially  rich  plexus  of  broad  capillaries  (sinusoids)  within  these  cell 
groups.  The  veins  return  the  islet  blood  by  a  similar  course. 

The  Lymphatics. 
—The  lymphatics  are 
mostly  confined  to  the 
interlobular  tissue, 
where  they  are  in  re- 
lation with  the  blood- 
vessels. 

The  Nerves.— The 
nerves     are     derived 
from  the  sympathetic 
system,  and  occur  as 
small    trunks    within 
the    interlobular    con- 
nective   tissue.      Nu- 
merous small  ganglia 
occur  in  their  course. 
As     in     the     salivary 
glands  the  nerves  sup- 
ply the  vascular  walls. 
About   the   secreting 
acini  they  form  a  del- 
icate   network    of 
naked    fibrils,    from 
which     end     branches 
penetrate    the    base- 
ment   membrane    and 
terminate     upon     the 
secreting  cells.     Lam- 
ellar corpuscles  are  oc- 
casionally found  in  the  interlobular  connective  tissue  of  the  pancreas. 
Resume. — Finally  the  attention  of  the  student  should  be  specially 
directed  to  the  presence  of  the  pancreatic  islets,  the  centro-acinar  cells, 
the  very  distinct  inner  granular  and  outer  fibrillar  zones  of  the  secreting 
cells,  the  thick  walls  of  the  interlobular  ducts,  the  absence  of  intralobular 
ducts  except  of  the  intercalary  type,  and  the  loose  character  of  the  inter- 
lobular tissue  as  the  distinguishing  characteristics  of  the  pancreas. 


FIG.  377. — SECTION  OF  A  PANCREATIC  ISLET  FROM 
INJECTED  SPECIMEN  OF  CAT'S  PANCREAS  TO  SHOW 
THE  PROFUSE  BLOOD  SUPPLY. 

The  capillaries  were  accurately  drawn  by  aid  of  a 
camera  lucida.  Only  the  nuclei  of  the  islet  cells  are 
indicated;  one  acinus  is  shown  at  the  left.  X  500. 


THE  LIVER 


405 


THE  LIVER 


The  liver  is  the  largest  gland  of  the  body,  and  may  be  classed  as  a 
peculiar  form  of  compound  tubular  gland  whose  cells  resemble  the  serous- 


FIG.  378. — A  LOBULE  OF  THE  PIG'S  LIVER;  THE  CENTRAL  VEIN  LIES  IN  THE  MIDDLE 
OF  THE  FIGURE. 

a,  capsule  of  Glisson.     Hematein  and  eosin.     Photo.     X   115. 

secreting  type.  The  organ  is  invested  with  a  connective  tissue  sheath, 
the  greater  portion  of  which  is  clothed  with  peritoneal  epithelium. 
From  this  connective  tissue  capsule,  fibrous  bands  or  septa  are  continued 
into  the  substance  of  the  organ  and  permeate  to  all  its  portions.  These 
processes  of  connective  tissue,  collectively  forming  the  capsule  of  Glisson, 
are  most  abundant  at  the  transverse  fissure  where  Iliev  contain  the  larn'e 


406 


THE  DIGESTIVE  SYSTEM 


blood-vessels  and  hepatic  ducts — this  fissure  serving  as  a  hilum  for  the 
organ.  The  liver  is  very  irregular  in  outline  and  shape,  and  comprises 
five  so-called  lobes  of  very  unequal  size.  In  the  adult  its  weight  is 


Central  vein 


FIG.  379. — DIAGRAM  OF  LIVER  LOBULES,  THE  UPPER  Two  Cur  TRANSVERSELY, 
THE  LOWER  LONGITUDINALLY. 

The  portal  veins  are  blue  striped;  the  hepatic  veins  (central  with  branches,  and 
sublobular)  are  solid  blue;  the  hepatic  arteries  are  red;  and  the  bile  canals  black. 
(After  Merkel.)  Cells  not  indicated. 


about  one-fortieth  that  of  the  body,  aboiit  3  to  3%  pounds.  The 
parenchyma  of  the  organ  arises  from  a  tubular  outgrowth  of  the  embry- 
onic duodenum,  hence  entodermal ;  the  interstitial  tissue  develops  in 
part  from  the  meseuchyma  of  the  caudal  layer  of  the  primitive  dia- 


THE  LIVER 


407 


phragm  (septum  transversum)  and  of  the  intervening  ventral  mesentery 
throughout  which  the  entodermal  tubules  ramify,  and  in  part  (the  retic- 
ulum)  from  endothelium  of  the  original  venous  sinusoids  (Mall). 

The  liver  is  dependent  for  its  structural  characteristics  upon  the 
peculiar  disposition  of  the  connective  tissue  of  Glisson's  capsule,  as  also 
of  the  blood-vessels  whose  branches  it  contains;  for  by  these  tissues  the 
substance  of  the  liver  is  ex- 
tensively subdivided  into  mi- 
nute   collections    of    hepatic 
cells,  each  group  forming  an 
anatomic    unit,    the    liepatic 
lobule,  which  in  addition  to 
the  hepatic   cells   contains  a 
connective    tissue    retioulum 
and  the  smaller  blood-vessels 
and  secretory  capillaries  (bile 
canaliculi). 

The  hepatic  lobules  are 
of  cylindrical  shape,  about  2 
millimeters  in  length  and  1 
millimeter  in  diameter  (Bai- 
ley). In  transverse  section 
they  present  a  polygonal 
(hexagonal  or  pentagonal) 
outline.  In  the  dog  they  are  Jones.) 
short  polyhedra  about  0.7 

millimeter  high,  and  0.7  millimeter  in  diameter;  the  entire  liver  con- 
taining 480,000  (Mall,  Amer.  Jour.  Anat,  5,  3,  190G).  They  are  anal- 
ogous to  the  lobules  of  compound  tubulo-acinar  glands,  inasmuch  as  they 
contain  the  secreting  parenchyma  of  the  organ,  but  are  very  different 
from  the  latter  in  the  arrangement  of  the  secreting  cells  which,  in  the 
human  liver,  do  not  present  either  a  tubular  or  acinar  structure,  but 
form  solid  c^l  columns.  Thus  in  the  human  liver  the  tubular  character 
of  the  gland  is  scarcely  apparent,  yet  in  the  liver  of  many  of  the  lower 
animals,  notably  in  that  of  the  turtle  and  frog,  the  cells  form  typical 
tubules  within  the  indistinct  hepatic,  lobules. 

The  bile  formed  by  the  liver  cells  is  conveyed  to  the  duodenum  by 
an  excretory  system,  beginning  with  inntmierahle  interlohular  bile  ducts 
which  receive  the  intralobular  secretory  capillaries,  and,  leaving  the 
lobule  from  all  its  sides,  find  their  way  through  the  inlerlohular  con- 


FIG.  380. — FROM  A  SECTION  OF  THE  TURTLE'S 
LIVER,  SHOWING  THE  TUBULAR  ARRANGE- 
MENT OF  THE  PARENCHYMA. 

a,  blood  capillary,  partially  filled  with  clotted 
blood;  b,  vascular  endothelium;  c,  darkened 
central  portions  of  the  hepatic  cells;  d,  periph- 
eral portion  of  the  hepatic  cells.  Osmium 
tetroxid;  carmin.  X  400.  (After  Shore  and 


408 


THE  DIGESTIVE  SYSTEM 


nective  tissue  of  the  capsule  of  Glisson  and  unite  with  their  fellows  to 
form  larger  and  larger  bile  ducts,  which  finally  join  to  form  the  main 
excretory  or  hepatic  duct;  the  latter  unites  with  the  cystic  duct  of  the 
gall-bladder  to  form  the  common  bile  duct  through  which  the  bile 
reaches  the  intestine.  The  gall-bladder — which  is  in  principle  a  diver- 
ticulum  from  the  hepatic  duct — is  simply  a  reservoir  for  the  storage  of 
bile;  it  is- absent  in  some  animals,  for  example,  the  horse  and  the  ele- 
phant. In  all  their  course  the  bile  ducts  are  in  close  relation  with  the 

radicals  of  the  portal 
,  6  vein  and  of  the  hepatic 
artery  —  the  group  of 
vessels  which,  together 
with  their  supporting 
(interlobular)  connec- 
tive tissue  and  the  in- 
cluded nerve  and  lymph 
channels,  form  the  so- 
called  portal  canals. 

The  Hepatic  Con- 
nective Tissue. — T  h  e 
hepatic  connective  tis- 
sue, or  the  supporting 
tissue  of  the  liver,  in- 
cludes the  capsule  of 
the  organ  and  the  cap- 
sule of  Glisson — the  lat- 
ter forming  a  frame- 
work throughout  the 
liver  and  inclosing  its 

hexagonal  lobules — together  with  the  more  delicate  intralobular  reticu- 
lum.  These  tissues  convey  the  blood-vessels,  lymphatics,  nerves,  and 
bile  ducts. 

The  fibrous  framework,  which  forms  both  the  outer  fibrous  capsule 
of  the  liver  and  the  capsule  of  Glisson,  contains  both  collagenous  and 
elastic  tissue,  the  latter  being  fairly  abundant — a  fact  which  sharply 
contrasts  with  the  complete  absence  of  elastic  fibers  from  the  interior  of 
the  hepatic  lobules. 

The  intralobular  connective  tissue  is  extremely  delicate,  and  consists 
of  very  fine  fibrils  and  stellate  cells  (of  von  Kupfer)  which  form  a  deli- 
cate reticulum,  in  which  the  capillary  blood-vessels  and  columns  of  liver 


FIG.  381. — THE  RETICULUM  OF  THE  DOG'S  LIVER. 

a,  central  vein ;  b,  capsule  of  Glisson  at  the  margin 
of  the  lobule.  Gold  chlorid.  X  120.  (After  Bohm 
and  von  Davidoff.) 


THE  LIVER  409 

cells  are  suspended.  The  anastomosing  strands  of  reticulum  converge 
from  the  periphery  toward  the  center  of  the  lobule,  thus  following  the 
course  of  the  blood  capillaries  and  cell  columns.  This  reticular  tissue 
(Mall)  exists  in  so  small  a  quantity  and  is  so  extremely  delicate  that 
although  it  can  be  readily  studied  after  removal  of  the  liver  cells,  as  by 
artificial  digestion,  in  ordinary  preparations — except  those  of  extreme 
thinness — it  can  scarcely  be  discovered  in  the  minute  clefts  between  the 
cell  columns  and  the  blood  capillaries.  It  differentiates,  at  least  in  part, 
from  the  endothelium  of  the  original  venous  sinusoids;  the  stellate  cells 
seen  in  Golgi  preparations  also  represent  endothelial  elements.  The 
endothelial  cells  of  the  intralobular  capillaries  are  actively  phagocytic. 
The  volume  of  the  interlobular  connective  tissue  which  forms  Glis- 
son's  capsule  varies  greatly  in 
different  animals.  In  the  liver 
of  the  pig  and  the  camel  this 
tissue  is  very  extensive,  and 
forms  a  complete  investment  for 
each  lobule.  In  man  it  is  very 
limited  in  amount  and  is  con-  J( 
fined  to  minute  areas  between 
the  adjacent  angles  of  the  lo- 
bules, with  an  occasional  frag-  FIG.  382.— STELLATE  CELLS  OP  VON  KTTP- 
ment  separating  the  lateral  sur-  FER  IN  THE  LIVER  OF  A  DOG. 

faces  of  neighboring  lobules.     It         g,  capillary  blood-vessel;  I,  hepatic  cells; 

is  in  the  latter  portions,  viz.,  be-     f '  f  ell^rc1flls;     Gold  chlorid-      X  200' 

'  (After  Kolhker.) 

tween  the  opposed  surfaces  of 

the  lobules,  that  the  branches  of  the  hepatic  veins  (sublobular  veins) 
are  found.  The  interlobular  veins,  the  subdivisions  of  the  portal  vein, 
together  with  the  bile  ducts  and  the  branches  of  the  hepatic  artery 
are  found  at  the  angles  of  adjacent  lobules;  hence  the  portal  canals, 
which  contain  these  vessels,  should  always  be  sought  in  this  location, 
while  the  sublobular  veins,  which  run  alone  and  -form  no  part  of  the 
portal  canals,  will  be  found  between  the  opposed  surfaces  of  the  lobules. 

The  capsule  of  Glisson  also  contains  many  lymphatic  vessels  and  non- 
medullated  nerve  fibers. 

The  Hepatic  Lobule.— The  lobule  is  the  structural  unit  of  the 
liver  and  consists  chiefly  of  hepatic  cells  which  are  arranged  in  radiating 
cords.  In  shape  the  lobule  is  an  irregularly  hexagonal  pyramid,  the 
exact  number  of  its  faces  being  extremely  variable.  The  periphery  of 
the  lobule  is  outlined  by  the  connective  tissue  of  Glisson's  capsule  which 


410 


THE  DIGESTIVE  SYSTEM 


cither  completely  invests  each  lobule,  as  in  the  pig's  liver,  or  forms  only 
a  very  incomplete  investment,  as  in  the  liver  of  man. 

Blood  enters  the  lobule  from  the  vessels  of  the  portal  canals  and 
finds  its  way,  through  converging  capillaries,  from  the  periphery  to  the 
center  of  the  lobule.  Here  it  enters  the  intralobular  or  central  vein, 


FIG.  383. — A  LOBULE  OF  THE  PIG'S  LIVER  IN  LONGITUDINAL  SECTION,  SHOWING 
THE  RELATION  OF  THE  CENTRAL  AND  SUBLOBULAR  VEINS  AND  THE  ARRANGEMENT 
OF  THE  HEPATIC  CELLS. 
a,  sublobular  vein;  6,  capsule  of  Glisson.    Hematein  and  eosin.    Photo.     X  66. 

which  occupies  the  axis  of  the  lobule  and  conveys  the  blood  thence  to  the 
sublobular  veins,  which  again  lie  in  the  interlobular  connective  tissue  of 
Glisson's  capsule. 

The  hepatic  cells  occupy  the  meshes  of  the  intralobular  capillaries 
(sinusoids)  and  are  arranged  in  cords  which  radiate  from  the  central 
vein  toward  the  periphery.  The  frequent  anastomoses  of  the  capillaries 


TIIK  LIVER 


411 


as  they  approach  the  central  vein  produce  great  irregularities  in  the 
arrangement  and  length  of  the  cell  cords.  Each  cord,  however,  reaches 
the  periphery  of  the  lobule  after  a  more  or  less  tortuous  course,  and  it 
is  here  that  the  secretory  bile  capillaries,  which  are  found  within  the 
cell  cords,  become  continuous  with  the  minute  bile  ducts  of  the  portal 
canals. 


FIG.  384. — A  LOBULE  OF  THE  HUMAN  LIVER,  SEEN  IN  TRANSECTION. 

It  is  outlined  by  three  small  portal  canals  and  contains  a  single  central  vein. 
Hematein  and  eosin.     Photo.     X  50. 

THE  BILE  CAPILLARIES. — The  bile  capillaries  occur  as  secretory 
canaliculi  between  the  opposed  surfaces  of  the  hepatic  cells.  They  are 
thus  found  within  the  cell  cords  and  stand  in  the  same  relation  to  the 
hepatic  cells  as  though  each  cell  cord  formed  a  tubule  whose  capillary 
lumen,  the  bile  canaliculus,  was  surrounded  by  only  two  secreting  cells, 
whereas  in  other  tubular  glands  a  larger  number  of  cells  encircle  the 
lumen  of  the  secreting  tubule.  Hence  the  bile  canaliculi  and  the  blood 
capillaries  are  never  in  contact,  but  are  always  separated  by  at  least 
one-third  to  one-half  the  diameter  of  a  hepatic  cell.  The  bile  canaliculus 
occurs  on  that  surface  of  the  hepatic  cell  which  is  in  contact  with  other 


412 


THE  DIGESTIVE  SYSTEM 


'*•»-  '  #^>.    ''--M. 


cells  within  the  cord;  the  blood  capillary,  on  the  other  hand,  is  in  rela- 
tion with  that  surface  of  the  hepatic  cell  which  forms  the  periphery  of 
the  cell  cord. 

The  blood  capillaries  are  suspended  in  the  fine  meshes  of  the  delicate 
reticulum  which  has  already  been  described  as  the  intralobular  connective 
tissue,  and  which  also  invests  the  cords  of  hepatic  cells.  This  reticular 
connective  tissue  is  of  relatively  insignificant  volume. 

The  bile  capillaries  are  true  secretory  canaliculi  by  which  the  bile, 

after  secretion  by  the 
hepatic  cells,  finds  its 
way  along  the  anastomos- 
ing cell  cords  to  some 

H?if  ,tS     '•  £      v  "*W^^   P°int  at  the  Periphery  of 

the  lobule,  where  the  cell 
cord  becomes  continuous 
with  a  minute  bile  duct, 
the  secreting  cells  within 
the  lobule  presenting  a 
rapid  transition  to  the 
very  low  columnar  or 
flattened  epithelium  of 
the  interlobular  bile 
duct.  The  immediate- 
lining  of  the  intralobular 
bile  canaliculus  is  a  del- 
icate cuticular  mem- 
brane, probably  the  prod- 
uct of  the  hepatic  cell. 

The  Hepatic  Cells. 
— These  are  large  poly- 
hedral cells  which  possess  one,  or  very  frequently  two,  spherical  nuclei 
and  a  coarsely  granular  cytoplasm.  A  true  cell  membrane  may  be  re- 
garded as  being  absent,  yet  there  is  often  a  sharply  defined  exoplasm 
which  forms  the  surface  of  the  cell  and  simulates  a  true  membrane. 

The  nuclei  of  the  hepatic  cells  are  rich  in  chromatin,  and  stain 
deeply.  They  are  situated  well  within  the  cell,  but  usually  in  an  eccentric 
position.  Frequently  they  contain  a  distinct  nucleolus. 

The  cytoplasm  of  the  hepatic  cells  is  finely  reticular,  the  meshes 
being  filled  with  coarse  granules  of  irregular  size.  Many  of  these  are 
undoubtedly  glycogenic  granules,  and  show  a  decided  color  reaction  when 


FIG.  385. — SECTION  OF  LIVER  TISSUE  OF  CAT, 
SHOWING  THE  LIVER  CELL-CORDS,  AND  THE  ARTI- 
FICIALLY ENLARGED  SINUSOIDS  LINED  WITH  ENDO- 
THELIUM.  X  375. 


THE  LIVER 


413 


Blood  capillary 


Bile  capillary 


Lymph  space 


treated  with  Lugol's  solution  of  iodin  after  alcoholic  fixation.     The 

amount  of  glycogen  present  varies  with  the  diet.     After  digestion  and 

absorption    of    a    carbohydrate 

meal  it  is  greatly  increased,  but 

disappears  during  fasting.   Even 

when  glycogen  is  quite  deficient, 

the  hepatic  cells  still  present  a 

granular   appearance   from   the 

presence    of    other    substances, 

possibly  zymogens. 

FAT     GLOBULES. — Fat    glo- 
bules occur  in  hepatic  cells  in     FIG.  386.— DIAGRAM   OP  FOUR  ADJACENT 
limited  numbers,  and  appear  to  LIVER  CELLS. 

be  a  normal  constituent.      The  (Adapted  from  Merkel.  ) 

globules  vary  much  in  size,  but 

are  all  very  small.  Their  number  is  also  dependent  upon  diet  and  diges- 
tion. During  absorption  of  a  fatty  meal,  fat  globules  occur  in  consider- 
able numbers,  and  are  most  numerous  in  those  hepatic  cells  which  are 


am 


FIG.  387. — ISOLATED  LOBULES  OP  THE  PIG'S  LIVER.  X12.5 
(After  F.  P.  Johnson;   Am.  Jour.  Anat.,  Vol.  23,  1918.) 


at  the  periphery  of  the  lobule.     They  are  not  normally  found  in  the 
vicinity  of  the  central  vein. 

The  hepatic  cells  also  frequently  contain  brown  or  yellowish-brown 


414 


THE  DIGESTIVE  SYSTEM 


FIG.  388. — SHOWING  THE  CONNECTION  BETWEEN  THE  INTRALOBULAR  AND  INTER- 
LOBULAR  BILE  DUCTS  IN  THE  CAT'S  LIVER. 

a,  interlobular  vein;  b,  interlobular  bile  duct;  c,  intralobular  bile  capillaries. 
Golgi  stain  and  hematein.    Highly  magnified.    (After  Geberg.) 


granules  of  ferruginous  PIGMENT,  which  are  more  prone  to  occur  in 
the  interior  of  the  lobule  near  the  central  vein.  When  present  in  con- 
siderable amount  this  pigment  can  no 
longer  be  considered  a  normal  constit- 
uent of  the  hepatic  cell.  Mitochondria 
have  also  been  described  in  the  hepatic 
cell  (Policard,  Compt.  Eend.  de  Soc.  et 
BioL,  1,  66,  1909).  An  intracellular 
canalicular  apparatus  can  also  be  dem- 
onstrated within  the  cytoplasm.  By 
some  these  channels  have  been  inter- 
preted as  intracellular  terminals  of  the 
intercellular  (intralobular)  bile  canal- 
iculi,  by  others  as  fixation  artifacts, 
and  still  others  regard  them  as  a  tro- 
phospongium.  Schaffer  (1902)  inter- 
prets them  in  part  as  channels  in  rela- 
tion with  the  blood  sinusoids.  Such  in- 
tracellular canaliculi  undoubtedly  ap- 
pear under  certain  functional  conditions,  but  it  is  uncertain  whether 
they  are  definite  preformed  channels,  or  simply  transient  secretory  canals. 


FIG.  389. — TYPES  OF  CELLS  FROM  A 
SECTION  OF  THE  NORMAL  *HUMAN 
LIVER. 

A,  the  usual  type  of  liver  cell;  B, 
fatty,  and  C,  pigmented  cells. 
Types  B  and  C  were  very  scarce. 
Hematein  and  eosin.  X  900. 


THE  LIVER 


415 


FIG.  390.  —  HUMAN 
LIVER  CELL,  SHOW- 
ING ENLARGED  IN- 
TRACELLTTLAR  CAN- 
ALICULI,  A  CONDI- 
TION CHARACTERIS- 
TIC OF  JAUNDICE. 
(Browicz.) 


Moreover,  it  seems  probable  that  the  canals  described  include  structures 

of  different  significance. 

The  Portal  Canals.  —  The  portal  canals  are  formed  by  the  ramifica- 

tions of  the  portal  vein,  hepatic  artery,  and  hep- 

atic duct,  and  are  characteristic  of  the  liver  —  the 

peculiarity  consisting  not  so  much  in  the  structure 

of  the  tissue,  as  in  the  combination  of  artery,  duct, 

and  vein  occurring  in  close  relation,  in  the  con- 

nective tissue  at  the  angles  of  the  hepatic  lobules. 

The  largest  vessel  in  the  canal  is  invariably  the 

vein,  the  smallest  the  artery. 

THE  INTERLOBULAR  VEINS.  —  The  interlobular 

veins,  branches  of  the  portal,  are  extremely  thin- 

walled  sinusoidal  vessels.      They  are  formed  by 

scarcely  more  than  the  endothelial  lining,  which 

is  supported  by  the  connective  tissue  of  Glisson's 

capsule.     Their  wall  contains  very  little  or  no 

smooth  muscle. 

THE  INTERLOBULAR  ARTERIES.  —  The  interlobular  arteries,  branches 
of  the  hepatic,  are  very  small  and  are 
noted  for  their  highly  developed  mus- 
cular coat  and  distinct  elastic  mem- 
brane. They  give  off  minute  vaginal 
branches  which  supply  capillaries  to 
the  tissue  of  Glisson's  capsule. 

THE  INTERLOBULAR  BILE  DUCTS.  — 
The  interlobular  bile  ducts,  radicals  of 
the  hepatic  duct,  receive  the  bile  from 
the  intralobular  bile  canaliculi  and 
convey  it,  through  larger  and  larger 
branches,  to  the  hepatic  duct.  They 
are  more  numerous  than  the  interlobu- 
lar veins  and  much  more  numerous 
than  the  interlobular  arteries.  Due  to 
their  frequent  branching  many  of  the 
P°rtal  —Is  as  seen  in  transverse  sec- 
tion  contain  two  bile  ducts.  The  ducts 
are  lined  by  columnar  epithelium 

whose  height  varies  with  the  size  of  the  tubule,  the  smallest  ducts  being 

lined  by  low  columnar,  or  cuboidal,  the  largest  by  tall  columnar  cells; 


FIG.  391. — DIAGRAM  OF  A  PORTAL 
CANAL,  INCLUDING  A  BRANCH  OF 
THE  PORTAL  VEIN,  HEPATIC  AR- 


MEDULLATED  NERVE  TRUNKS. 


416 


THE  DIGESTIVE  SYSTEM 


the  lining  epithelium  of  the  hepatic,  cystic  and  common  bile  ducts  is 
very  tall.  The  epithelial  cells  of  the  ducts  possess  characteristic  spherical 
or  ovoid  nuclei  which  are  heavily  loaded  with  chromatin.  Their  cyto- 
plasm is  clear  or  finely  reticular.  The  largest  ducts  contain  a  few  goblet 


FIG.  392. — FROM  A  SECTION  OP  THE  RABBIT'S  LIVER  WHOSE  BLOOD-VESSELS  HAD 
BEEN  INJECTED  WITH  A  CARMIN  STAINED  GELATIN  MASS;  SOMEWHAT  MORE 
THAN  A  SINGLE  LOBULE  is  REPRESENTED. 

a,  interlobular  veins;  b,  central  vein;  c,  central  vein  from  which  the  injection 
mass  had  fallen  out;  the  capillaries  are  dark.    Photo.     X  70. 

cells;  small  mucous  glands  are  found  in  the  hepatic  and  common  bile 
duct. 

The  epithelium  of  the  interlobular  bile  ducts  rests  upon  a  thin  base- 
ment membrane,  which  is  surrounded  by  a  thick  fibre-elastic  coat.  The 
larger  ducts  are  also  supplied  with  circular  smooth  muscle  fibers,  which, 
in  the  largest  branches,  form  a  considerable  coat.  Outside  of  the  liver. 


THE  LIVEE  417 

longitudinal  muscle  fibers  also  appear  in  the  walls  of  the  excretory 
ducts,  and  so  accumulate  in  the  wall  of  the  gall-bladder  and  common 
bile  duct  as  often  to  form  a  distinct  layer. 

As  has  been  pointed,  out  by  Mall  (190G)  the  hepatic  lobule  cannot  be 
regarded  as  the  homologue  of  the  lobule  of  other  glands.  For  the  portal 
canal  with  its  bile  duct,  the  excretory  duct  of  the  glandular  unit,  should 
be  axial  to  the  functional  lobular  unit.  Moreover,  an  interlobular  bile 
duct  drains  not  the  whole  of  a  particular  lobule,  but  portions  of  a  num- 
ber of  adjacent  lobules.  The  functional  unit  (portal  lobule),  in  contra- 
distinction to  the  structural  unit  -(hepatic  lobule),  is  accordingly  that 
portion  of  liver  tissue  (portions  of  a  number  of  hepatic  lobules)  sup- 
plied by  an  ultimate  branch  of  the  vessels  of  a  portal  canal.  Thus  a 
hepatic  lobule  is  drained  by  several  bile  ducts,  and  conversely,  a  single 
ultimate  bile  duct  drains  portions  of  several  hepatic  lobules. 

Blood  Supply. — The  liver  is  supplied  with  blood  from  two  inde- 
pendent sources,  the  hepatic  artery  and  the  portal  vein.  That  supplied 
by  the  artery  is  of  minor  importance  and  is  destined  only  for  the  nutri- 
tion of  the  connective  tissue  framework  of  the  organ. 

On  entering  the  liver  at  the  transverse  fissure,  the  HEPATIC  ARTERY 
gives  off  numerous  capsular  branches  which  ramify  in  the  capsule  of  the 
liver  and  supply  capillaries  to  its  connective  tissue.  Other  branches,  the 
direct  continuation  of  the  hepatic  artery,  enter  the  portal  canals  and  by 
repeated  division  form  the  interlobular  arteries,,  which  ramify  in  the 
tissue  of  Glisson's  capsule,  and  whose  vaginal  branches  supply  capillaries 
to  this  connective  tissue.  These  capillaries,  as  well  as  those  from  the 
capsular  branches,  become  continuous,  at  the  periphery  of  the  lobule,  with 
the  intralobular  capillaries  which  are  derived  from  the  branches  of  the 
portal  vein. 

THE  PORTAL  VEIN. — The  portal  vein  likewise  enters  at  the  transverse 
fissure,  bringing  to  the  liver  the  blood  collected  from  the  capillaries  of 
the  organs  of  digestion  and  absorption.  It  divides  into  numerous 
branches  which  follow  the  portal  canals,  in  which  they  are  known  as  the 
interlobular  veins,  and  in  this  way  reach  all  portions  of  the  organ. 

The  interlobular  veins  throughout  all  their  course  give  off  small 
branches  which  at  once  enter  the  periphery  of  the  hepatic  lobules  and 
immediately  break  into  a  brush  of  capillary  vessels.  These  intralobular 
capillaries  (capilliform  sinusoids,  Lewis)  converge  toward  the  center  of 
the  lobule  and  anastomose  to  form  a  capillary  network,  in  the  elongated 
meshes  of  which  are  the  cords  of  hepatic  cells.  These  capillaries  approach 
the  center  of  the  lobule  where  they  unite  to  form  the  iiitralobular  or 


418 


THE  DIGESTIVE  SYSTEM 


central  vein.  The  central  vein  frequently  begins  in  the  form  of  a  Y, 
its  two  or  more  branches  finally  uniting  to  form  a  single  vessel  which 
pursues  its  course  through  the  axis  of  the  -lobule.  The  central  vein 
makes  its  exit  at  the  periphery  of  the  lobule  and  enters  the  interlobular 
connective  tissue  where  it  unites  with  its  fellows  to  form  larger  sul- 
lobular  veins.  The  sublobular  are  easily  distinguished  from  the  inter- 
lobular veins  by  their  thicker  walls  and  by  the  fact  that  the  former 


FIG.  393. — A  GROUP  OF  SURFACE  LOBULES  OF  THE  PIG'S  LIVER. 

p.  v.,  portal  vein:  «.  v.,  sublobular  (hepatic)   vein;   c.  v.,  central  (hepatic)  vein. 

X1U.     (After  F.  P.  Johnson.) 


pursue  an  independent  course  through  the  tissue  of  Glisson's  capsule, 
being  nowhere  in  relation  with  either  artery  or  duct. 

The  sublobular  veins  are,  as  a  rule,  vessels  of  considerable  size,  and 
by  frequent  union  with  their  fellows  become  constantly  larger.  In  their 
general  direction  they  tend  toward  the  dorsal  surface  of  the  liver  and 
finally  make  their  exit  as  four  or  five  large  hepatic  veins  which  enter 
the  inferior  vena  cava. 

The  blood  supply  of  the  liver,  30  per  cent,  of  which  can  be  ac- 
counted for  in  the  hepatic  artery,  60  per  cent,  in  the  portal  vein  (Mac- 


THE    LIVER  419 

leod  and  Fearce,  Amer.  Jour.  Physiol.,  vol.  35,  1914),  is  peculiar  in 
that:  (1)  the  greater  portion  of  the  blood  has  already  passed  through 
the  capillaries  of  the  digestive  organs  before  entering  the  liver;  (2) 
its  arterial  supply  is  relatively  meager  and  supplies  only  the  connective 
tissue  framework,  intermingling  with  the  portal  blood  at  the  periphery 
of  the  lobule;  (3)  its  intralobular  capillaries  are  extremely  abundant 
and  are  in  intimate  relation  with  the  hepatic  cells,  each  cell  coming  into 
contact  with  four  to  six  capillary  vessels. 

The  course  of  the  blood  through  the  vessels  of  the  liver  will  be 
readily  appreciated  by  reference  to  the  following  table  which  indicates 
the  succession  of  the  hepatic  blood-vessels: 

1.  Portal  vein  1.    Hepatic  artery 

2.  Interlobular  veins  2.     Interlobular  arteries 

3.  Branches  to  lobule  3.     Vaginal  branches  and  capillaries 

in  Glisson's  capsule 

4.  Intralobular  capillaries 

5.  Central  vein  (intralobular) 

6.  Sublobular  veins 

7.  Hepatic  veins 

8.  Vena  cava  inferior 

The  three  classes  of  veins,  interlobular,  central,  and  sublobular  are 
readily  differentiated  by  the  fact  that  the  two  latter  lie  alone,  while  the 
interlobular  veins  are  always  in  company  with  the  ducts  and  arteries 
within  the  portal  canals.  Moreover  the  central  vein  has  almost  no  con- 
nective tissue  wall  until  near  its  exit  from  the  lobule,  where  it  passes 
into  the  sublobular  branches;  the  sublobular  veins,  on  the  other  hand, 
possess  a  relatively  thick  connective  tissue  wall  and  even  some  smooth 
muscle,  except  in  the  very  smallest,  which  are  to  be  regarded  as  mere 
interlobular  continuations  of  central  veins  which  soon  unite  to  form 
the  larger  sublobular  vessels. 

Lymphatics. — The  lymphatics  of  the  liver  may  be  considered  as  con- 
sisting of  a  superficial  set  which  supplies  the  hepatic  peritoneum  and 
the  capsule  of  the  liver,  and  which  is  continuous  with  a  deeper  set  in 
Glisson's  capsule.  The  lymphatics  of  the  deep  set  begin  as  perivascular 
spaces  within  the  lobule,  from  which  the  lymph  enters  larger  lymphatic 
vessels  in  the  interlobular  connective  tissue, 'which  follow  the  vessels  of 
the  portal  canals  to  their  exit  from  the  liver ;  the  larger  lymphatics  pass 
to  the  abdominal  lymph  nodes.  Other  lymphatics  follow  the  sublobular 
and  hepatic  veins  and  pass  to  the  mediastinal  lymph  nodes. 


420  THE  DIGESTIVE  SYSTEM 

Nerves. — The  nerves  of  the  liver  are  mostly  of  the  non-medullatcd 
variety.  They  follow  the  portal  canals  and  are  distributed  to  the  walls 
of  the  blood-vessels,  the  walls  of  the  bile  ducts,  and  to  the  capsule  of  the 
liver.  Naked  fibrils  from  these  trunks  also  enter  the  lobules  and  form 
a  plexus  among  the  hepatic  cells  (Korolkow, 
Anat.  Anz.,  1893),  in  relation  with  which  they 
form  fine  terminal  brushes  and  varicose  end 
knobs  (Berkley,  Johns  Hop.  Hosp.  Eep.,  1895). 
The  liver  secretes  the  bile — a  fluid  which  aids 
in  the  digestion  and  absorption  of  fats — and  in 
fact  probably  serves  also  an  excretory  role.  Bile 
has  a  greenish -yellow  color,  due  in  part  to  the 

FIG.    394. INTRALOB-     presence  of  the  pigment  bilirubin,  which  is  be- 

ULAR  NERVE  FIBERS     lieved  to  be  identical  with  the  hematoidin  elab- 
IN  A  RABBIT'S  LIVER.     Qrated  from  the  hcmoglobin  Of  tne  erythroplas- 

a,    hepatic    cells;    6,     ^s  disintegrating  in  the  spleen,  and  carried  to 
nerve  fiber.    Golgi  stain.      ..-',.         ,  .  , .          .      .          n          .  , 

Highly  magnified.     (Af-     the  liver  DJ  waj  01  the  splenic  and  portal  veins, 
ter  Berkley.)  Under  certain  pathological  conditions  known  as 

jaundice,  bile  finds  its  way  within  the  liver  di- 
rectly into  the  blood  stream  where  it  produces  hemolysis  of  the  red 
corpuscles.  In  addition  to  its  bile-producing  activity,  the  liver  functions 
also  as  an  organ  of  internal  secretion,  in  the  conversion  of  glycogen  into 
sugar  and  the  elaboration  of  urea.  Experimental  evidence  indicates  that 
the  liver  is  concerned  greatly  also  with  the  production  of  fibrinogen 
(Whipple,  Amer.  Jour.  Physiol.,  1914). 


THE  GALL-BLADDER 

The  wall  of  the  gall-bladder  consists  of  three  coats:  (1)  mucous; 
(2)  muscular;  (3)  fibroserous.  The  mucous  membrane  is  markedly 
folded  or  corrugated,  the  irregularly  polygonal  depressions  being  rela- 
tively broad  at  the  fundus  but  becoming  narrower  toward  the  neck  of  the 
organ.  The  lining  epithelium  is  of  the  tall  columnar  variety,  with 
spheroidal  or  ovoid  nuclei  which  lie  near  the  base  of  the  cell.  The  free 
extremity  of  the  epithelial  cells  presents  an  indistinct  cuticular  border. 
The  epithelium  follows  all  the  folds  of  the  mucosa  and  lines  the  inter- 
vening depressions. 

The  corium  of  the  mucosa  consists  of  delicate  connective  tissue  and 
contains  a  few  smooth  muscle  fibers  derived  from  the  muscular  coat. 


THE  GALL-BLADDER 


421 


FIG.  395. — FROM  A  SECTION  THROUGH  THE  WALL  OF  A  DOG'S  GALL-BLADDER. 
a,  epithelium;  b,  lymph  nodule;  c,  serous  coat.     X  80.     (After  Sudler.) 

It  is  connected  with  the  nrascularis  by  a  thin  layer  of  denser  connective 
tissue  which  contains  blood  and  lymphatic  vessels  and  which  simulates  a 
submucosa. 


FIG.  396. — RECONSTRUCTION  OF  THE  WALL  OF  A  DOG'S  GALL-BLADDER. 
a,  vein;  b,  artery;  c,  lymphatic  vessel;  d,  epithelium.     X  60.     (After  Sudler.) 

The  gall-bladder  possesses  a  distinct  muscular  wall,  consisting  of 
numerous  interlacing  smooth  muscle  bundles  the  most  of  which  are  cir- 
cularly disposed.     Occasionally  they  form  fairly  distinct  circular  and 
longitudinal  layers. 
27 


422  THE  DIGESTIVE  SYSTEM 

The  fibroserous  coat  consists  of  loose  areolar  tissue,  which  contains 
the  larger  blood-vessels  with  which  the  organ  is  abundantly  supplied. 
The  free  surface  of  the  gall-bladder  also  receives  a  peritoneal  investment. 

Occasional  mucous  glands  occur  in  the  mucosa  of  the  gall-bladder. 
These  are  mostly  of  small  size  and  widely  separated,  but  toward  the  neck 
of  the  organ  they  increase  in  both  number  and  size.  They  form  short, 
branched,  convoluted  tubules. 

The  blood-vessels  form  a  plexus  just  outside  the  muscular  coat,  from 
which  branches  are  distributed  to  the  peritoneal  coat  and  to  a  plexus  in 
the  depth  of  the  mucosa  from  which  capillaries  are  supplied  to  the  muscu- 
lar layers  and  to  a  subepithelial  plexus.  The  nerves  are  distributed  to 
the  blood-vessels  and  to  the  muscular  wall.  Minute  ganglia  occur  in  the 
muscular  coat. 

The  gall-bladder  is  lacking  in  many  species  of  vertebrates  includ- 
ing the  lamprey,  pigeon,  rat.  horse,  certain  ruminants  and  the  porpoise. 
In  these  instances  a  well-differentiated  cystic  anlage  suffers  regressive 
changes  in  later  embryonic  life  and  ultimately  disappears.  With  the 
disappearance  of  the  gall-bladder,  the  biliary  system  generally  under- 
goes compensatory  enlargement.  Dilatation  of  the  bile  ducts  is  fre- 
quently associated  with  congenital  absence  of  the  gall-bladder  in  the 
human  subject,  and  commonly  follows  cholecystectomy  (see  Scammon, 
Anat.  Rec.,  10,  8,  1916). 


CHAPTER    XIV 
THE   UKINARY   SYSTEM 

This  system  includes  the  kidneys,  which  are  two  large  hean-shaped 
glands,  together  with  their  excretory  passages,  the  ureters,  which  conduct 
the  urine  to  the  urinary  bladder.,  whence  it  is  voided  through  the  urethra. 

THE  KIDNEY 

Each  kidney  is  a  gland  of  the  compound  tubular  type,  measuring 
about  four  and  one-half  inches  in  length,  two  and  one-half  inches  in 
width,  and  one  and  one-half  inches  in  thickness.  Its  secretion,  the  urine, 
is  produced  by  the  uriniferous  or  renal  tubules,  which  are  long  tortuous 
canals  beginning  near  the  surface  of  the  kidney  and  finally  ending  at 
the  hilum  of  the  organ  where  they  pour  their  secretion  into  the  calyces 
of  the  renal  pelvis.  The  uriniferous  tubules  are  in  intimate  relation 
with  the  renal  blood-vessels  which  supply  rich  capillary  plexuses  to  the 
entire  extent  of  the  tubules.  Each  uriniferous  tubule  consists  of  both 
tortuous  and  straight  portions,  and  these  are  so  regularly  disposed  as  to 
produce  macroscopical  variations  in  the  appearance  of  the  different  por- 
tions of  the  renal  parenchyma  according  as  the  tortuous  or  the  straight 
portions  of  the  tubules  predominate.  These  variations  result  in  the  fol- 
lowing topographical  subdivisions. 

TOPOGRAPHY  OF  THE  KIDNEY 

If  the  kidney  be  divided  parallel  to  its  long  axis  by  an  incision  extend- 
ing from  its  convex  surface  to  the  hilum,  the  cut  surface  shows  that  the 
parenchyma  is  divisible  into  a  superficial  cortex  and  a  central  medulla. 
The  slit-like  hilum  of  the  organ  opens  into  a  deep  excavation,  the  renal 
sinus,  which  is  occupied  by  the  renal  pelvis  and  its  subdivisions,  the 
infundibula  and  calyces,  into  which  the  medulla  projects  in  the  form 
of  several  conical  pyramids.  The  pelvis  of  the  kidney,  the  expanded 

423 


424 


THE  URINARY  SYSTEM 


funnel-form  beginning  of  the  ureter,  toward  the  renal  parenchyma 
divides  into  two,  sometimes  three,  infundibula,  which  in  turn  subdivide 
into  several  calyces,  each  of  which  incloses  the  conical  apex  of  a  projecting 
medullary  or  renal  (Malpighian)  pyramid. 

The  Medulla. — The  medulla  of  the  kidney  consists  of  a  number  of 
these  conical  renal  pyramids  (usually  twelve  to  fifteen)   each  of  whose 

apices,  as  already  stated,  is  received 
into  the  extremity  of  a  renal  calyx. 
Occasionally  a  calyx  may  receive  two 
papilla?.  The  base  of  each  pyramid 
is  embedded  in  the  adjacent  renal 
cortex,  and  that  portion  of  the  cor- 
tex which  is  interposed  between  the 
bases  of  adjacent  pyramids,  and  thus 
brought  into  relation  with  the  fi- 
brous and  adipose  tissue  which  en- 
velops the  pelvis  and  calyces  at  the 
hilum  of  the  organ,  composes  the 
cortical  renal  columns  (of  Bertini). 
Each  renal  pyramid  may  be  sub- 
divided into  a  central  free  portion, 
the  apical  or  papillary  zone  of  the 
medulla,  which  is  received  into  a 
calyx,  and  an  outer  or  basal  portion, 
which  is  embedded  in  the  renal  cor- 
tex and  is  known  as  the  boundary 
zone  of  the  medulla.  These  two  por- 
tions of  the  medulla,  the  papillary 
and  boundary  zones,  can  be  readily 


FIG.  397. — LONGITUDINAL  SECTION  OF 
KIDNEY. 

1,  cortex;  1',  cortical  rays;  1",  laby- 
rinth; 2,  medulla;  2',  papillary  portion 
of  medulla;  2",  boundary  layer  of  me- 
dulla; 3,  transverse  section  of  tubules 
in  the  boundary  layer;  4,  fat  of  renal 
sinus;  5,  artery;  *,  renal  column  of 
transverse  medullary  rays;  A,  branch 
of  renal  artery;  C,  renal  calyx;  U,  ureter. 
(After  Tyson  and  Henle,  from  Hill.) 


distinguished,  since  the  latter  con- 
tains only  narrow  tubules  and  is 
highly  vascular,  while  the  former, 
relatively  deficient  in  blood-vessels, 
contains  the  broad  terminations  of 

the  uriniferous  tubules,  the  papillary  ducts  (of  Bellini)  which  converge 
toward  the  apex  of  the  pyramid  where  they  open  into  the  calyces. 

The  Cortex. — The  cortex  of  the  kidney,  on  careful  observation,  pre- 
sents numerous  dark  lines  or  delicate  columns  which  radiate  from  the 
base  of  the  pyramids  outward  toward  the  surface  of  the  organ.  These 
radiating  columns  are  the  medullary  rays  (pyramids  of  Ferrein)  or 


THE  KIDNEY 


425 


pars  radiata  of  the  cortex.  They  contain  straight  portions  of  the  urinif- 
erous  tubules;  these  are  continuous  with  the  similar  tubules  in  the 
boundary  zone  of  the  medulla.  These  columns  lie  within  the  cortex  and 
not,  as  their  name  might  be  taken  to  indicate,  in  the  medulla.  They 
are  termed  'medullary  rays' 
because  of  their  peculiar  rela- 
tion to  the  medulla,  from 
which  they  extend  outward  in 
a  radial  direction.  It  would 
seem  more  proper  to  desig- 
nate them  'cortical  rays.' 

That  portion  of  the  cortex 
which  invests  the  cortical 
rays  and  which  includes  all 
the  remaining  cortical  por- 
tions of  the  organ,  consists  of 
extremely  tortuous  tubules, 
and  is  characterized  by  the 
presence  of  small  globular 
bodies,  each  of  which  con- 
tains a  tuft  of  capillary  ves- 
sels. These  are  the  renal 
corpuscles  (Malpigliian  bod- 
ies] which  are  characteristic 
of  the  kidney.  The  portion 
of  the  cortex  in  which  they 
occur  includes  the  entire  cor-  A 

tical  substance  with  the  ex-  FIG.  398. — DIAGRAM  OF  THE  STRUCTURE  OF 
ception  of  the  cortical  rays,  THE  KlDNEY- 

and  is  known  as  the  renal  °»  Papillary  zone,  and  b,  boundary  zone  of 
,  7  .  ,  the  medulla;  c,  cortex;  1,  apex  of  a  renal 

labyrinth  or  pars  convoluta.  pyramid;  2,  capsule;  3,  tubules  of  the  me- 
The  labyrinth  is  divided  dulla;  4,  vasa  rectse;  5,  vascular  arcades;  6,  a 
into:  (1)  the  renal  columns,  cortical  ray;  7,  labyrinth;  *  interlobular  ar- 
tery; 9,  renal  corpuscle;  10,  'cortex  corticis.' 
already  mentioned;  (2)  the  (After  Testut.) 

intercolumnar    portions,     or 

labyrintli  proper,  which  includes  that  portion  of  the  labyrinth  which 
invests  the  cortical  rays,  and  which,  in  sections  cut  parallel  to  these 
columns  (longitudinal  sections)  appears  as  a  portion  of  cortex  inserted 
between  the  adjacent  rays;  (3)  a  narrow  boundary  zone  of  the  cortex, 
'cortex  corticis  of  Hyrtl,  which  is  included  between  the  fibrous  capsule 


426 


THE  UKINAEY  SYSTEM 


of  the  organ  and  the  tips  of  the  cortical  rays,  and  in  which  the  renal 
corpuscles,  though  present,  are  relatively  few  in  number. 

The  Renal  Lobule. — In  fetal  and  infantile  life  the  kidney  is  dis- 
tinctly lobed.  This  condition  is  permanent  in  some  animals — e.g.,  rep- 
tiles, birds,  porpoise,  ox,  bear — each  lobe  consisting  of  a  renal  pyramid 
with  its  related  portion  of  cortical  substance.  In 
man,  after  the  first  year,  the  renal  lobes  com- 
pletely fuse  and  eventually  leave  scarcely  a  trace 
of  the  early  lobed  condition. 

Internally  this  fetal  lobed  condition  is  in  part 
indicated  by  the  definitive  renal  pyramids,  from 
eight  to  eighteen  in  number,  each  representing  the 
product  of  fusion  of  from  two  to  nine  primitive 
lobes.  In  certain  mammals — e.g.,  mouse,  rabbit, 
cat,  guinea  pig — neither  a  primitive  nor  definitive 
internal  or  external  lobar  arrangement  appears. 
Such  kidneys  are  designated  unipyramidal  or  uni- 
papillary,  in  contradistinction  to  the  multipapil- 
lary  type.  In  certain  of  the  perissodactyls  (ele- 
phant, horse)  no  distinct  pyramids  are  present. 

The  term  renal  lobule  or  renculus,  as  applied 
to  the  adult  human  kidney,  refers  to  a  still  smaller 
subdivision  of  the  organ,  one  which  includes  a 
single  cortical  ray  together  with  that  portion  of  the  cortical  labyrinth  by 
which  it  is  immediately  invested.  Its  peripheral  boundary  is  marked  by 
the  interlobular  blood-vessels.  This  lobule  is  the  anatomical  unit  of  the 
kidney  and  is  thus  comparable  to  the  portal  and  to  the  pulmonary  lobule, 
except  that  its  arterial  supply  enters  at  the  periphery.  The  tortuous 
secreting  portions  of  its  uriniferous  tubules  are  contained  in  the  laby- 
rinth at  the  periphery  of  the  lobule,  while  its  straight  conducting  por- 
tions lie  in  the  cortical  ray  in  the  axis  of  the  lobule.  The  larger  inter- 
lobular arteries  and  veins  lie  at  the  periphery,  where  they  supply 
branches  to  several  adjacent  lobules. 


FIG.  399.  —  RECON- 
STRUCTION OF  A  URI- 
NIFEROUS TUBULE 
OF  AN  INFANT.  (After 
Stoerk.) 


THE  KENAL  CONNECTIVE  TISSUES 

The  kidney  is  enveloped  by  a  fibrous  capsule,  the  tunica  fibrosa, 
which  is  loosely  attached  to  the  substance  of  the  organ  and  contains  the 
usual  proportion  of  elastic  fibers  together  with  a  little  smooth  muscle. 
A  fatty  layer,  the  tunica  adiposa,  invests  the  capsule.  At  the  hilum  of 


THE  KIDNEY  427 

the  organ  the  capsule  is  continuous  with  the  connective  tissue  which 
envelops  the  renal  pelvis,  inf'undiliula.  and  calyces,  and  which,  in  the 
interval.-  hetwren  adjacent  calyces,  comes  into  relation  with  the  cortical 
substances  of  the  renal  columns. 

This  connective  tissue  of  the  hilum  is  of  the  areolar  variety  and 
contains  much  adipose  tissue.  It  supports  the  large  arteries  and  veins 
as  they  pass  along  the  surface  of  the  renal  pelvis  on  their  way  to  and 
from  the  renal  columns,  where  they  enter  or  leave  the  parenchyma. 
Sympathetic  nerve  fibers  and  a  few  small  ganglia  are  also  found  in  this 
region. 

The  connective  tissue  of  the  interior  of  the  organ,  interstitial  tissue, 
is  very  scanty,  and  in  most  parts  consists  only  of  isolated  fibrils  which 
invest  the  blood-vessels  and  the  renal  tubules.  It  forms  a  very  delicate 
reticulum  by  which  the  walls  of  the  uriniferous  tubules  are  loosely  united. 
If  the  epithelium  of  these  tubules  is  removed,  a  delicate  fibrous  network 
remains ;  this  network  incloses  a  homogeneous  basement  membrane  upon 
which  the  lining  epithelium  ordinarily  rests.  Elastic  fibers  scarcely 
occur  among  the  tubules  of  the  kidney.  The  interstitial  tissue  is  slightly 
increased  in  amount  about  the  larger  blood-vessels,  the  renal  corpuscles 
of  the  cortex,  and  the  small  blood-vessels  of  the  boundary  zone  of  the 
medulla.  At  the  apex  of  the  renal  pyramid  it  invests  the  large  papillary 
ducts  in  considerable  quantity. 


THE  URINIFEROUS  OR  RENAL  TUBULES 

The  uriniferous  tubules  begin  in  the  cortical  labyrinth  as  the  capsules 
of  the  renal  corpuscles.  Assuming  a  tubular  form  they  then  pursue  a 
tortuous  course  through  the  pars  convoluta  and  finally  enter  the  boundary 
zone  of  the  medulla,  where,  much  reduced  in  size,  they  form  the  loop  of 
Henle,  which  consists  of  a  short,  descending,  thin  limb,  a  U-shaped  loop, 
and  a  long,  ascending  or  thick  limb.  This  last  division,  after  recrossing 
the  boundary  zone  of  the  medulla,  enters  a  pars  radiata  and  returns 
to  the  region  of  its  origin,  where  it  becomes  again  convoluted.  A  short 
arched  tubule  connects  this  convoluted  portion  with  a  straight  collecting 
hilnilc  of  the  cortical  ray.  The  collecting  tubules  traverse  the  whole 
length  of  the  ray,  uniting  with  their  fellows  and  receiving  other  arched 
tubules  along  their  entire  course.  They  then  cross  the  boundary  zone 
of  the  medulla,  and  finally,  in  the  papillary  zone,  having  meanwhile 
received  numerous  accessions  of  straight  collecting  tubules,  form  the 


428 


THE  URINARY  SYSTEM 


large   terminal  tubules,   the   papillary   ducts,   which   pour  the   urinary 
secretion  into  the  renal  calyces. 

Each  uriniferous  tubule  may  thus  be  subdivided  into  several  portions 


Arched  collecting 
tubule 


Vas  afferent      Vas  efferens 


Intercalary  (dis-  ) 
tal  convoluted)  V 
segment  ) 


Proximal  conto- 
luted  segment 


Renal  corpuscle 


Vasa  arci/ormia 

Stout,  clear  por-  ) 

tion  of  loop  of  [ 

Henle  '  \ 


Interlobar 
blood-vessels 

Stout,cloudy  por- 
tion of  loop  of 
Henle 


Slender,  clear) 
portion  of  loop  V 
of  Henle  } 


Henle' s  loop 

Large,  straight 
collecting  in- 
bule  ) 


Glomerulus 
Cortex 

i  Straight,  colli-ct- 

(      ing  tubule 

Interlobular  vein 
Interlobular  artery 

Arteriola  recta 
Outer  stripe 

<  Outer     zone     of 
t      medulla 

Inner  stripe 


5  Inner     zone     of 
i     medulla 


Papilla 


FIG.  400. — DIAGRAM  OF  URINIFEROUS  TUBULE  OF  A  MAMMAL.     (Adapted  from 
Peter  and  Merkel.) 


which  differ  from  each  other,  not  only  in  their  location,  but  also  in  the 
character  of  their  lining  epithelium.  The  successive  portions  which 
compose  a  single  uriniferous  tubule  may  be  enumerated  as  follows : 


THE  KIDNEY 


429 


1.  Capsule  of  the  renal  corpuscle. 

2.  K"eck  of  the  tubule. 

3.  Proximal  convoluted  portion. 

4.  Descending  limb  of  Henle's  loop. 

5.  Loop  of  Henle.     Medullary  loop. 

6.  Ascending  limb  of  Henle's  loop. 

7.  Distal  convoluted  portion. 

8.  Arched  collecting  tubule. 

9.  Straight  collecting  tubule. 
10.  Papillary  duct. 

It  should  be  borne  in  mind  that  all  of  these  several  portions  form 
only  successive  parts  of  a  single  uriniferous  tubule.  Those  portions  of 
the  urine  which  are  secreted  into  the  capsule  of  the  renal  corpuscle 
must  therefore  find  their  way  through  each  of  these  successive  portions 
before  it  can  reach  the  excretory  passages  of  the  renal  calyces,  pelvis, 
and  ureter. 

1.  The  Renal  Corpuscle  (Malpighian  Body). — A  renal  corpuscle 
consists  of  a  spherical  tuft  of  capillary  vessels,  the  glomerulus,  which  in 
the  course  of  its  development 
is  invaginated  into  the  end  of 
the  uriniferous  tubule,  and 
thus  comes  to  be  enveloped  by 
a  double  layer  of  flattened  epi- 
thelial cells  known  as  the  glom- 
erular  capsule  (of  Bowman). 

The  inner  visceral  layer  of 
the  capsule  closely  invests  the 
entire  surface  of  the  glomeru- 
lus,  except  at  that  point  where 
the  afferent  and  efferent  vessels 
enter  and  leave  the  capillary 
tuft;  at  this  point  the  visceral  FlG"  401. -RECONSTRUCTION  OF  A  GLOMER- 

ULUS  OF  THE  HUMAN  KIDNEY. 
epithelium  is  reflected  outward 

and  becomes  continuous  with 
the  parietal  layer.  The  sur- 
faces of  these  two  layers  are  almost  in  apposition ;  the  narrow  interval 
between  them  which  results  from  the  slightly  eccentric  position  of  the 
glomerulus  forms  the  first  portion  of  the  lumen  of  the  uriniferous  tubule. 
At  that  pole  of  the  renal  corpuscle  which  is  opposite  the  entrance  of  its 


a,  afferent  arteriole;  b,  efferent  arteriole; 
c,  capillaries.     X  444.     (After  Johnston.) 


430 


THE  URINARY  SYSTEM 


blood-vessels  the  capsule  opens,  through  a  narrow  neck.,  into  the  first  or 
proximal  convoluted  portion  of  the  uriniferous  tubule. 

The  glomerulus  is  a  true  arterial  rete  mirabile,  since  it  receives  an 
afferent  artery,  which,  after  forming  the  capillaries  of  the  glomerulus, 


%&?  Kp*w'' 

:^M 


FIG.  402. — FROM  THE  CORTICAL  LABYRINTH  (PARS  CONVOLTJTA)  OF  THE  HUMAN 
KIDNEY. 

A  large  renal  corpuscle  is  in  the  center  of  the  figure.  At  its  upper  border  are 
several  sections  of  distal  convoluted  tubules.  The  great  majority  of  the  tubules 
shown  are  from  the  proximal  convoluted  portions,  a,  a  portion  of  a  glomerulus; 
b-b,  parietal  layer  of  the  capsule;  c,  proximal  convoluted  tubules;  d,  just  within 
this  point  is  a  transection  of  a  junctional  tubule  having  relatively  low  and  clear 
epithelium  and  a  broad  lumen.  Hematein  and  eosin.  Photo.  X  135. 

passes  out  as  an  efferent  artery  to  again  enter  a  capillary  plexus  about 
the  neighboring  tubules  of  the  renal  cortex.  The  afferent  vessel  is  of 
somewhat  larger  caliber  than  the  efferent — a  noteworthy  fact  because  of 
its  relation  to  the  intraglomerular  blood  pressure. 


THE  KIDNEY  431 

On  entering  the  glomerulus  the  artery  divides  into  two  vessels  which 
immediately  subdivide  with  the  formation  of  five  branches  (Johnston). 
Each  of  these  branches  forms  a  series  of  anastomosing  capillary  loops 
whose  convexity  is  directed  away  from  the  entering  artery.  The  capillary 
loops  reunite,  in  a  similar  manner,  to  form  the  efferent  vessel,  which 
leaves  the  glomerulus  in  company  with  the  afferent;  but,  once  out,  they 
soon  part  company,  the  efferent  vessel  breaking  into  a  second  capillary 
plexus  about  the  neighboring  tubules.  Within  the  glomerulus  the  capil- 
laries are  united  by  a  very  delicate  but  scanty  connective  tissue  containing 
no  elastic  fibers. 

The  visceral  layer  of  the  capsule  is  firmly  adherent  to  the  walls  of 
the  glomerular  capillaries.  It  consists  of  a  single  layer  of  flat  epithelial 
cells  which  are  intimately  blended  with  each  other  and  with  the  endothe- 
lium  of  the  capillaries.  The  epithelial  cells  possess  a  clear  cytoplasm  and 
a  flattened  ovoid  nucleus,  which,  being  thicker  than  the  body  of  the 
cell,  produces  a  considerable  bulging.  In  fetal  and  infantile  life  the 
shape  of  the  cells  of  this  layer  is  cuboidal  or  even  low  columnar,  but 
becomes  more  and  more  flattened  as  development  progresses,  until  the 
epithelium  finally  simulates  a  layer  of  endothelial  cells. 

The  epithelium  of  the  parietal  layer  is  also  cuboidal  in  fetal  life, 
but  during  development  becomes  nearly  as  much  flattened  as  that  of  the 
visceral  layer.  Its  single  layer  of  finely  granular  cells  forms  a  complete 
lining  for  the  capsule.  It  rests  upon  a  homogeneous  basement  membrane 
which  is  invested  by  a  thin  layer  of  connective  tissue.  This  fibrous  layer 
is  rather  more  highly  developed  about  those  renal  corpuscles  which  lie 
near  the  medulla  than  about  those  of  the  more  peripheral  portions  of 
the  cortex. 

2.  The  Neck  of  the  Tubule. — In  this  portion  of  the  tubule  the 
flattened  epithelium  of  the  glomerular  capsule  rapidly  changes  to  the 
low  columnar  type  of  the  proximal  convoluted  portion.     This  section  is 
extremely  short;  it  forms  a  constricted  portion  which  marks  the  begin- 
ning of  the  tortuous  tubule.     This  constriction  is  more  apparent  than 
real,  since  the  caliber  of  the  tubule  in  the  neck  is  as  great  as  in  the 
succeeding  portion  whose  external  diameter  is,  however,  much  increased 
by  the  increasing  height  of  the  epithelial  cells.     This  portion  of  the 
tubule,  being  in  relation  with  the  renal  corpuscle,  is  necessarily  found 
in  the  cortical  labyrinth. 

3.  The  Proximal  Convoluted  Portion. — This    is    commonly    the 
longest  and  broadest  portion  of  the  urinil'croiis  tubule.     Collectively  the 
convoluted  tubules  form  the  greater  part  of  the  cortical  labyrinth,  in 


432 


THE  URINARY  SYSTEM 


which  region  only  they  occur.  This  portion  of  the  tubule  is  remarkable 
for  the  irregularity  of  its  course,  it  being  twisted  and  bent  upon  itself  in 
a  most  tortuous  manner.  Arising  at  the  renal  corpuscle,  it  at  first  passes 
toward  the  surface  of  the  organ,  but  soon  turns  about  and  runs  toward 


FIG.  403. — FROM  THE  CORTEX  OF  THE  HUMAN  KIDNEY,  SHOWING  A  TRANSECTION 
OF  A  CORTICAL  RAY  IN  THE  LOWER  LEFT-HAND  CORNER. 

a,  glomerulus;  6,  glomerular  capsule;  c,  proximal  convoluted  tubule;  d,  collecting 
tubule;  e,  ascending  limb  of  Henle's  tubule;/,  spiral  tubule;  g,  blood-vessel;  h,  distal 
convoluted  tubule.  Hematoxylin.  X  200.  (After  Schaper,  from  Stohr.) 


the  medulla,  at  first  with  extreme  convolutions,  but  later  pursuing  a 
rather  spiral  course  (spiral  tubule).  On  reaching  the  border  of  the 
medulla  the  tubule  becomes  sharply  constricted  and  enters  the  medullary 
boundary  zone  at  the  thin  descending  limb  of  Plenle's  loop. 


THE  KIDNEY 


433 


The  epithelium  of  the  convoluted  tubule  is  of  the  columnar  or  pyram- 
idal type,  its  cells  having  broad,  firmly  united  bases  and  conical  free 
apices.  The  lateral  margins  of  the  cells  are  often  so  intimately  blended 
at  the  base  as  to  resemble  a  syncytium.  When  isolated,  or  if  outlined 
by  impregnation  with  silver  salts,  the  borders  of  the  epithelial  cells  are 
extremely  irregular  and  are  deeply  fluted  or  serrated,  the  serrations  of 
each  cell  interdigitating  with  those  of  its  neighbors.  The  deep  fluted  ser- 


FIG.  404. — FROM  A  LONGITUDINAL  SECTION 
OF  A  CONVOLUTED  TUBULE  OF  THE 
GUINEA-PIG'S  KIDNEY. 

The  cell  outlines  have  been  blackened  by 
the  Golgi  method.  Very  highly  magnified. 
(After  Landauer.) 


FIG.  405. — CROSS  SECTION  OF  A 
PROXIMAL  CONVOLUTED  TUBULE 
FROM  THE  KIDNEY  OF  A  MOUSE, 
SHOWING  BASAL  FILAMENTS 
(PROBABLY  LARGELY  MITOCHON- 
DRIAL)  BREAKING  UP  INTO  GRAN- 
ULES CENTRALLY,  AND  THE  CEN- 
TRAL STRIATED  BORDER  OF  THE 
CELLS. 

Meves'     mitochondrial    technic. 
X  1000. 


rations  of  the  interlocked  epithelium  gives  many  of  its  cells  a  coarsely 
striated  appearance,  the  striation  being  more  prominent  beneath  the 
centrally  situated  nucleus  than  in  the  apical  portion  of  the  cell.  Other 
longitudinal  striations  in  the  proximal  or  basal  portion  of  the  cell  are 
the  result  of  a  linear  arrangement  of  granules  and  filaments  which  occur 
in  this  part.  These  appearances  often  give  the  epithelium  of  the  convo- 
luted tubules  a  peculiar  striated  or  'rodded'  character.  The  granules  and 
filaments  are  probably  largely  mitochondrial  in  nature. 

The  apices  of  the  epithelial  cells  are  very  easily  destroyed,  but  when 


434  THE  URINARY  SYSTEM 

perfectly  preserved  often  present  a  delicately  striated,  cuticular  border 
('brush  border').  The  remaining  portions  of  the  cytoplasm  are  finely 
granular. 

The  nuclei  of  the  epithelial  cells  of  the  convoluted  tubules  are  spheri- 
cal in  shape,  and  do  not  stain  very  deeply  with  nuclear  dyes  as  compared 
with  the  more  distinct  and  deeply  staining  nuclei  of  the  collecting 
tubules.  Thus  they  appear  as  if  partially  clouded  by  the  granular  cyto- 
plasm, an  appearance  which  is  greatly  exaggerated  with  the  onset  of  acute 
inflammatory  processes,  which,  on  attacking  the  kidney,  are  prone  to 
involve  the  convoluted  tubules.  The  chromatin  is  quite  evenly  distributed 
throughout  the  nucleus  and  the  nuclear  membrane  is  not  easily  demon- 
strated. 

The  lumen  of  the  convoluted  portion  of  the  uriniferous  tubule  is  of 
variable  caliber;  it  presents  frequent  slight  dilatations.  The  caliber  also 
depends,  to  some  extent,  upon  the  secretory  activity  of  the  epithelium, 
whose  cells  become  shrunken,  and  the  lurnen  correspondingly  dilated, 
during  active  secretion.  The  diameter  varies  from  40  to  60  microns. 
The  convoluted  tubules  are  most  actively  engaged  in  the  secretion  of 
urine,  but  the  further  changes  accompanying  their  secretion  have  not 
yet  been  satisfactorily  demonstrated.  It  is  generally  believed  that  the 
water  and  salts  of  the  urine  are  secreted  in  the  glomerular  capsule,  the 
urea  in  the  convoluted  tubules. 

4.  Descending  Limb  of  Henle's  Tubule  (The  Thin  or  Narrow  Tu- 
bule of  Henle). — In  this  portion,  which  is,  typically,  located  in  the 
boundary  zone  of  the  medulla,  the  uriniferous  tubule  becomes  very  much 
narrowed  (8-15 p.),  but  the  decreased  diameter  is  the  result  of  dimin- 
ished height  of  the  lining  epithelium  rather  than  of  any  change  in 
the  caliber  of  the  tubule.  The  length  of  this  portion  of  the  tubule  is 
very  variable;  typically  it  corresponds  very  nearly  with  the  breadth  of 
the  medullary  boundary  zone. 

The  lining  epithelium  of  the  descending  limb  is  of  a  peculiar  flattened 
shape.  Its  cells  possess  an  ovoid  nucleus  which,  being  thicker  than  the 
surrounding  portions  of  the  cell,  projects  slightly  into  the  lumen  of  the 
tubule.  The  bulging  nuclei  of  opposite  sides  of  the  tubule  are  not  in 
apposition  but  interlock  with  one  another,  the  nuclei  of  one  side  of  the 
tubule  being  opposed  to  the  cell  margins  of  the  opposite  side.  The 
lumen  of  longitudinal  sections  through  the  axis  of  the  tubule  thus  ac- 
quires a  sort  of  zigzag  outline.  The  nuclei  stain  deeply  but  possess  an 
evenly  distributed  chromatin.  The  cytoplasm  of  the  epithelium  is  very 
finely  granular,  and  although  its  cells  are  intimately  adherent  at  their 


THE  KIDNEY  435 

lateral  margins  they  do  not  present  the  typical  stations  which  are 
characteristic  of  the  preceding  portion. 

5.  The  Loop  of  Henle. — As  the  descending  limb  enters  the  loop 
of  Henle,  the  tubule  makes  an  abrupt  turn  and  returns  toward  the  cortex. 
The  location  of  the  loop,  being  dependent  upon  the  variable  location  in 
the  cortex  of  the  renal  corpuscle  and  the  variable  length  of  the  thin  seg- 
ment, may  be  in  any  portion  of  the  medulla  except  the  extreme  tip  of  the 
pyramids;  its  most  frequent  site,  however,  is  near  the  junction  of  the 
boundary  and  papillary  zones. 

The  structure  of  the  loop  may  be  that  of  either  the  descending  or  the 
ascending  limb  of  the  typical  loop.  It  is  also  subject  to  great  variations, 
since  the  change  in  structure  from  the  narrow  to  the  broad  type,  though 
it  typically  occurs  just  prior  to  the  formation  of  the  loop,  is  frequently 
delayed  until  well  into  the  ascending  limb.  As  a  rule,  the  change  in 
type  occurs  earlier  when  the  loop  lies  in  the  boundary  zone,  and  later 
when  it  occurs  nearer  the  apex  of  the  renal  pyramid ;  the  thick  ascending 
limbs  do  not  occur  in  the  papillary  zone  of  the  medulla. 

6.  The  Ascending  Limb  of  Henle 's  Loop  (The  Broad  or  Thick 
Limb). — This  portion  of  the  tubule  returns  through  the  boundary  zone 
of  the  medulla  and  enters  a  cortical  ray,  its  course  being  parallel  to 
that  of  the  descending  limb.     It  then  passes  toward  the  surface  of  the 
kidney,  but  finally  leaves  the  ray  and  enters  the  labyrinth  to  reach  that 
renal  corpuscle  (close  to  the  vas  efferens)  from  which  the  uriniferous 
tubule  took  origin,  and  in  relation  to  which  the  tubule  again  acquires 
a  tortuous  course   (distal  convoluted  portion).     Within  the  boundary 
zone  of  the  medulla  this  portion  of  the  tubule  is  much  broader  than  the 
preceding  division,  but  it  becomes  somewhat  reduced  in  size  in  its  course 
through  the  cortical  ray. 

The  epithelium  of  the  ascending  limb  is  of  a  short  cuboidal  form. 
Its  cytoplasm  resembles  that  of  the  lining  epithelium  of  the  convoluted 
portion,  although  the  nuclei  in  the  tubule  of  Henle  are  rather  more  dis- 
tinct. Basal  striations  are  also  less  distinct  than  in  the  convoluted  tu- 
bule, the  lateral  serrations  less  deep,  and  the  cell  outlines  sharper.  The 
cells  of  this  portion  frequently  possess  a  slightly  imbricated  arrange- 
ment. 

The  recent  careful  comparative  studies  of  mammalian  kidneys  by 
Peter  ("Untersuchungen  iiber  Bau  and  Entwickelung  der  Niere,"  Jena, 
1909)  have  revealed  certain  important  details.  Peter  divides  the  medullary 
portion  of  the  renal  pyramid  into  an  outer  and  inner  zone;  these  portions 
have  no  precise  correspondence  with  the  boundary  and  papillary  zones  above 


436 


THE  URINARY  SYSTEM 


mentioned.  In  the  outer  zone  Peter  describes  an  outer  and  an  inner  stripe, 
the  line  of  demarcation  being  the  very  definite  level  where  the  proximal 
convoluted  tubule  passes  into  the  thin,  clear,  narrow  limb  of  Henle's  loop 
(Fig.  400).  The  point  of  transition  from  outer  to  inner  zone  is  marked  by  a 
change  in  the  character  of  the  epithelium  lining  the  distal  limb  of  the  long 
Henle's  loops;  the  epithelium  becomes  cloudy  (granular)  and  thicker.  In 
view  of  the  great  variability  in  the  character  of  the  epithelium  at  the  vari- 


tf£3  ^£$ 

K^m  * 

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FIG.  406. — A  GROUP  OF  TUBULES  FROM  A  TRAN SECTION  OF  A  RENAL  PYRAMID  OF 
THE  HUMAN  KIDNEY;  THE  SECTION  PASSES  THROUGH  THE  BOUNDARY  ZONE. 

a,  collecting  tubule;  b,  ascending  limb  of  Henle's  loop;  c,  descending  limb;  d,  loop 
of  Henle.    Hematein  and  eosin.    Photo.     X  275. 

ous  levels  in  loops  of  different  lengths,  and  the  recognition  by  Peter  of  a 
thicker  cloudy  segment,  it  seems  better  to  speak  of  thin  clear,  thick  clear, 
and  thick  cloudy  segments  of  the  loop.  In  kidneys  of  the  dog  and  cat 
there  are  no  really  short  loops,  none  lying  within  the  outer  zone.  In  the 
kidney  of  the  pig  many  loops  lie  in  the  cortex;  such  loops  lack  entirely 
the  thin,  clear  narrow  limb. 

7.  The  Distal  Convoluted  Portion  (Intercalary  or  Intermediate 
Portion}. — This  portion  of  the  uriniferous  tubule  begins  close  to  the 
vascular  pole  of  the  renal  corpuscle,  and,  after  several  irregular  contor- 


THE  KIDNEY  437 

tions  which  are  confined  to  the  region  of  the  cortical  labyrinth,  enters 
an  arched  collecting  tubule..  The  distal  is  much  shorter  than  the  proxi- 
mal convoluted  portion.  Its  caliber  is  subject  to  great  irregularities,  so 
much  so  that  its  early  turns  have  been  characterized  as  the  irregular  or 
zigzag  portion  of  the  uriniferous  tubule.  The  epithelium  of  this  section 
resembles  that  of  the  proximal  convoluted  portion  but  is  lower,  more 
cuboidal,  and  striations  are  indistinct. 

This  portion  terminates  the  typically  secretory  portion  of  the  urinif- 
erous tubule.  Beyond  here  the  tubule  possesses  more  the  function  of  a 
duct,  hence  its  epithelium  shows  a  decided  change  in  character.  Hith- 
erto it  has  possessed  the  peculiar  character,  the  typically  granular  cyto- 
plasm, of  a  secreting  type  of  cell.  Beyond  this  section  the  epithelium  is 
no  longer  so  granular  but  possesses  a  characteristically  clear  appearance. 
The  secretory  and  excretory  portions  of  the  renal  tubule  have  a  separate 
embryonic  origin,  and  only  secondarily  unite  to  form  a  continuous  duct. 

8.  The  Arched  Collecting  Tubule   (Junctional  Tubule).— This  is 
a  short  portion  of  the  uriniferous  tubule  which  connects  the  distal  con- 
voluted portion  in  the  cortical  labyrinth  with  the  straight  collecting  tu- 
bules of  the  cortical  rays.    Its  course  is  characteristically  arched. 

The  epithelium  of  the  arched  tubule  consists  of  clear  cuboidal  cells 
with  distinct  outlines  and  deeply  stained,  sharply  defined  nuclei.  The 
chromatin  of  the  nucleus  is  irregularly  distributed,  forming  numerous 
karyosomes,  and  the  nuclear  membrane  is  distinct.  The  cytoplasm  is 
relatively  devoid  of  granules,  and  unlike  that  of  the  secreting  epithelium 
does  not  possess  a  strong  affinity  for  the  acid  dyes. 

9.  The  Straight  Collecting  Tubules. — These  portions  of  the  tu- 
bules begin  in  the  cortical  rays,  where  they  receive  the  arched  tubules, 
and,  proceeding  to  the  medulla,  become  considerably  increased  in  size. 
They  penetrate  the  boundary  zone  of  the  medulla,  all  pursuing  a  parallel 
or  slightly  convergent  course,  and  occasionally  uniting  with  each  other. 
On  entering  the  papillary  zone,  by  frequent  union  they  become  rapidly 
larger,  and  in  the  apex  of  each  pyramid  finally  form  about  a  score  of  large 
terminal  papillary  ducts.    Though  shorter  than  the  convoluted  tubules, 
the  straight  collecting  portions,  because  of  their  direct  course,  traverse 
a  broader  area  of  the  renal  tissue;  beginning  near  the  peripheral  end  of 
the  cortical  rays,  in  these  columns  they  cross  nearly  the  whole  breadth 
of  the  renal  cortex  and  entering  the  medulla  extend  from  base  to  apex 
of  the  renal  pyramid. 

Throughout  their  whole  course  they  progressively  increase  in  size  and 
caliber,  A  corresponding  progressive  increase  in  the  height  of  their  epi- 


438  THE  URINARY  SYSTEM 

thelial  cells  likewise  occurs,  so  that  the  lumen  of  the  straight  tubules 
of  the  medulla  is  not  only  actually  greater  than  that  of  those  of  the 
cortical  rays,  but  the  Avails  of  the  former  tubules  are  also  considerably 
thicker.  The  extreme  of  this  progression  is  found  in  the  broad  lumen 
and  tall  epithelium  of  the  papillary  ducts. 

The  epithelium  of  the  straight  tubules,  like  that  of  the  arched, 
possesses  a  clear  cytoplasm,  distinct  and  deeply  staining  chromatic 
nuclei,  and  well  defined  cell  outlines.  Beginning  'in  the  cortical  rays  with 
a  low  columnar  type,  it  gradually  increases  in  height  in  the  course  of 
the  tubule  until,  in  the  papillary  zone,  the  epithelium  acquires  a  tall 
columnar  form.  The  clear  cytoplasm  and  distinct  nuclear  membranes 
of  the  epithelium  of  the  collecting  tubules  stand  out  in  sharp  contrast  to 
the  granular  cytoplasm  and  the  evenly  distributed  chromatin  in  the 
nuclei  of  the  lining  cells  in  the  secreting  portions  of  the  uriniferous 
tubules. 

10.  Papillary  Ducts.  (Ducts  of  Bellini)  .—These  are  the  wide 
mouths  of  the  uriniferous  tubules  which  are  formed  by  the  dichot- 
omous  union  of  from  ten  to  thirty  collecting  tubules,  and  which  empty 
their  secretion  into  the  renal  calyces  at  the  apex  of  the  renal  pyramids. 
They  attain  a  diameter  of  from  two  hundred  to  three  hundred  microns. 
They  are  lined  by  tall  columnar  cells  with  an  exceptionally  clear  cyto- 
plasm which  has  an  affinity  for  the  basic  in  preference  to  the  acid  class 
of  dyes.  The  nuclei  are  spheroidal  or  ovoid  in  shape  and  lie  in  the 
basal  portion  of  the  cell.  At  their  termination  several  papillary  ducts 
frequently  open  into  a  common  depression  or  foveola  which  is  lined  by 
an  involution  of  the  layer  of  transitional  epithelium,  derived  from  that 
of  the  renal  calyx,  by  which  the  free  papillary  portion  of  the  renal  pyra- 
mid is  clothed. 

It  is  obvious  that  the  entire  renal  tubule,  from  the  glomerular  capsule 
to  the  papillary  duct,  is  a  continuous  canal  whose  epithelial  wall,  sup- 
ported by  a  thin  homogeneous  basement  membrane  varies  in  character 
in  each  succeeding  portion.  Thus  the  proximal  and  distal  convoluted 
portions  and  the  typical  ascending  limbs  of  Henle's  loops  possess  a 
granular,  rodded  or  striated,  acidophil,  secreting  epithelium;  the  capsule 
has  thin  cells  of  an  endothelioid  type;  the  typical  descending  limb  and  loop 
of  Henle  are  lined  by  flattened  finely  granular  and  faintly  acidophil 
epithelium;  the  curved  and  straight  collecting  tubules  and  papillary  ducts 
possess  a  clear  columnar  epithelium.  It  should  also  be  noticed  that  the 
several  portions  of  the  renal  tubule  occur  in  different  topographical  sub- 


THE  KIDNEY 


439 


divisions  of  the  kidney  and  that,   therefore,  each  of  the  subdivisions 
contains  only  certain  characteristic  portions  of  the  renal  tubule.     Thus 


are  found  in  the — 
CORTICAL  LABYRINTH. 
(1'ars  Convolute) 

CORTICAL  KAYS 

(Pars  radial  a) 

BOUNDARY  ZONE  OF  THE 
MEDULLA.  . 


1 1 enal  corpuscle. 
Neck  of  the  tubule. 
Proximal  convoluted  portion. 
Distal  convoluted  portion. 
Arched  collecting  portion. 

f  Spiral  portion  of  the  convoluted  tubule. 
J  Ascending  limb  of  Henle's  tubule. 
[Straight  collecting  portion. 

Descending  limb  of  Henle's  tubule. 
Ascending  limb  of  Henle's  tubule. 
'[Straight  collecting  portion. 

f  Descending  limb  of  Henle's  tubule. 
PAPILLARY  ZONE  OF  THE    Loop  of  Henle's  tubule. 

MEDULLA 1  Straight  collecting  portion. 

[  Papillary  duct. 


The  following  outline,  based  upon  the  investigations  of  Peter,  gives  a 
more  detailed  classification  of  the  different  portions  of  the  renal  tubule 
in  the  medulla  : 

1.  Outer  stripe 

(a)  straight  collecting  tubules. 

(b)  proximal  convoluted  tubules. 

A.  Outer  Zone  (c)     thick  ascending  limbs  of  Henle's  loops, 

including  both 

(x)     thick  cloudy  portions,  and 
(y)     thick  clear  portions. 

2.  Inner  stripe 

(a) 


MEDULLA- 


thin  clear  descending  limbs  of  Henle's 

loops. 
,       (b)     thick    cloudy    portion    of    ascending 

limbs  of  Henle's  loops. 
(c)     short  loops  of  Henle,  of  thick  cloudy 

type  of  epithelium. 
B.  Inner  Zone 

(a)  straight  collecting  tubules. 

(b)  long-  loops  of  Henle,  entirely  of  thin  clear  type  of 

epithelium. 


440 


THE  UEINAEY  SYSTEM 


The  following  tabular  resume  may  be  of  service  by  emphasizing  the 
more  important  peculiarities  of  the  several  portions  of  the  uriniferous 
tubule. 


PORTION  OF  TUBULE. 

EPITHELIUM. 

LOCATION. 

Renal  corpuscle. 

Flattened,  endothelioid. 

Cortical  labyrinth. 

Neck. 

Changing  from  flattened 

Cortical  labyrinth. 

to  low  columnar. 

Proximal  convoluted. 

Low  columnar,  granular, 

Cortical  labyrinth. 

and  rodded. 

Spiral  portion  of  above. 

Low  columnar,  granular, 

Cortical  rays. 

and  rodded. 

Descending  limb. 

Low    cuboidal    or    flat- 

Medulla   (boundary    and 

tened,  granular. 

papillary  zones). 

Loop. 

Varies;    like    either    the 

Medulla    (boundary    and 

Ascending  limb. 

preceding  or  following. 
Cuboidal  or  low  colum- 
nar,   granular,    imbri- 

papillary zones). 
Boundary    zone    of    me- 
dulla and  cortical  rays. 

cated. 

Distal  convoluted. 

Low  columnar  or  pyram- 

Cortical labyrinth. 

idal,  granular,  and  rod- 

ded. 

Arched  collecting. 

Cuboidal,      clear      cyto- 

Cortical labyrinth. 

plasm,  dark  nucleus. 

Straight  collecting. 

Cuboidal,     changing    to 

Cortical    rays    and    both 

columnar. 

zones  of  medulla. 

Papillary  duct. 

Cuboidal,  tall  columnar. 

Papillary  zone  of  medulla. 

RENAL  BLOOD-VESSELS,  LYMPHATICS  AND  NERVES 

Blood  Supply.  — The  kidney  receives  its  blood  supply  from  the  renal 
artery,  which,  as  it  enters  the  hilum,  divides  into  two  sets  of  principal 
branches,  of  which  the  ventral  set  supply  three-fourths,  the  dorsal  set 
one-fourth  of  the  renal  substance.  These  principal  branches,  the  arterice 
proprice  renales,  or  interlobar  arteries,  are  embedded  in  the  connective 
tissue  of  the  sinus  and  follow  the  walls  of  the  infundibula  and  calyces, 
upon  which  they  lie,  thus  reaching  the  renal  columns  between  the  renal 
calyces.  Here  they  enter  the  cortical  substances  and  divide,  each  branch 
passing  in  a  curved  or  arched  manner  beneath  the  base  of  the  adjacent 
pyramids.  These  vessels  form  an  incomplete  arterial  arcade  (arciform 
artery)  which  lies  in  the  margin  of  the  cortex  at  the  outer  border  of  the 
medullary  boundary  zone. 

From  the  arterial  arcade,  branches  are  given  to  the  medullary  tissue 
of  the  pyramids  on  the  one  hand,  and  on  the  other  to  the  cortical  sub- 
stance, Those  branches  which  enter  the  medulla  are  slender  vessels  which 


THE  KIDNEY 


441 


pursue  a  characteristically  straight  course  between  the  parallel  tubules 
of  this  region  and  are  known  as  the  arteriolce  recta.  They  branch  freely 
at  acute  angles  and  form  a  rich  capillary  plexus  in  the  boundary  zone, 
the  longest  of  the  vessels  reaching  beyond  the  limits  of  this  region  to 
supply  a  less  abundant 
plexus  to  the  papillary 
zone  of  the  medulla. 

The  cortical  branches 
of  the  arterial  arcades  are 
vessels  of  considerable  size 
which  enter  the  labyrinth 
between  the  cortical  rays 
and  as  interlobular  arteries 
(cortical  arterioles)  pass 
toward  the  surface  of  the 
organ,  a  few  of  the  longest 
branches  reaching  the  fi- 
brous capsule  with  whose 
vessels  they  anastomose. 
Throughout  their  whole 
course  the  interlobular  ar- 
teries give  off  numerous 
short  branches,  which 
leave  the  parent  stem  at  a 
wide  angle,  and  pass  di- 
rectly to  a  renal  corpuscle 
as  the  afferent  artery  (ar- 
tcriole;  vas  afferens)  to  its 
glomerulus.  Here  it  sup- 
plies the  capillary  plexus 
in  the  manner  already  de- 
scribed (page  431). 

Certain  of  the  afferent 
arterioles  are  peculiar  in 
that  (1)  they  give  off 

sum II  branches  which  supply  capillaries  directly  to  the  convoluted  tubules 
of  the  cortical  labyrinth;  and  (2)  they  occasionally  form  a  small  rete 
mirabilc  before  they  reach  the  glomerulus.  By  far  the  greater  portion 
of  the  branches  of  the  interlobular  arteries,  however,  pass  directly  to  the 
glomeruli.  The  capillaries  of  the  glomerulus  reunite  to  form  an  efferent 


FIG.  407. — THE  DISTRIBUTION  OF  THE  LEFT  RENAL 
ARTERY. 

Of  the  six  arterise  propriae  renales,  five  enter  in 
front  of  the  renal  pelvis,  and,  lying  upon  the  wall 
of  the  calyces,  are  distributed  from  the  arterial 
arcade  to  both  cortex  and  medulla,  a,  ureter;  b, 
renal  artery;  c,  arteriae  propriae  renales;  d,  the  dark 
border  is  the  cortex,  within  which  is  the  lighter 
medulla.  (After  Brodel,  from  Szymonowicz  and 
MacCallum.) 


442 


THE  UEINAEY  SYSTEM 


vessel  which,  after  leaving  the  corpuscle,  promptly  breaks  into  a  second 
capillary  plexus  about  the  adjacent  tubules. 

The  efferent  vessels  of  those  glomeruli  which  lie  in  that  portion  of 
the  cortex  adjoining  the  medulla,  frequently  pass  to  the  boundary  zone 
of  the  latter  region  where  they  form  the  arterias  rectae  spuria3  which, 
though  lacking  a  true  arterial  structure — they  possess  no  circular  mus- 


FIG.  408. — FROM  THE  CORTEX  OF  THE  HUMAN  KIDNEY. 

The  blood-vessels  have  been  injected  and  appear  dark.  A  cortical  ray  and  the 
adjacent  labyrinth  is  included,  a,  cortical  ray;  b,  a  glomerulus  in  the  labyrinth. 
Moderately  magnified.  (After  Disse.) 

cle  fibers — pursue  the  same  course  as  the  true  arteriolas  rectae  and  assist 
the  latter  in  supplying  the  capillary  plexus  of  the  medulla.  The  medul- 
lary capillaries,  like  those  of  the  rays  in  the  cortex,  form  a  network  with 
elongated  meshes  which  surround  the  parallel  tubules  of  this  region. 
The  capillaries  of  the  cortical  labyrinth,  being  distributed  among  irregu- 
lar tortuous  tubules,  possess  a  more  polygonal  mesh. 

The  interlobular  veins  begin  near  the  surface  of  the  organ  where 


THE  KIDNEY  443 

small  venules,  derived  from  the  cortical  capillaries  and  from  occasional 
anastomoses  with  the  capsular  vessels,  unite  to  form  broad  thin-walled 
venous  spaces,  the  stellate  veins  of  Verheyn,  just  beneath  the  capsule. 
From  these  subcapsular  vessels  the  interlobular  veins  arise,  and  pass 
toward  the  medulla  in  company  with  the  interlobular  arteries,  throughout 
their  course  collecting  the  minute  venules  which  return  the  blood  from 
the  capillaries  about  the  tubules  of  the  renal  cortex. 

xVrriving  at  the  border  of  the  medulla,  but  still  embedded  in  the 
cortical  substance,  the  interlobular  veins  turn  sharply,  at  nearly  right 
angles  to  their  former  course,  and  by  free  anastomoses  form  a  venous 
arcade  (arciform  vein),  which  receives  the  venulce  rectce  coming  from  the 
capillary  plexuses  of  the  medulla,  and  at  the  border  of  the  renal  pyra- 
mid enters  a  renal  column  to  unite  with  similar  vessels  coming  from  the 
borders  of  the  adjacent  pyramids.  The  union  of  these  vessels  forms 
large  venous  trunks  which  leave  the  renal  columns,  in  company  with 
the  arteries,  as  the  vence  proprice  renales  (interlobar  veins).  They  enter 
the  connective  tissue  of  the  hilum,  traverse  the  wall  of  the  calyces,  in- 
fundibula,  and  renal  pelvis,  and  finally  unite  to  form  the  renal  vein. 

*  TABLE  SHOWING  THE  COURSE  OF  THE  RENAL  CIRCULATION 

Renal  artery  Renal  vein 


I  t. 

!  renales  Venae  propri 

r       ~T 


Arteriae  propriee  renales  Venae  propriac  renales 


Arterial  arcade  Venous  arcade 


/        \  /        \ 

Interlobular  arteries         Arteriolse  rectae          Venulse  rectae       Interlobular  veins 


\     \ 


Capillaries  of  medulla 

Venso  stellatac          T 


Afferent  artery  to  renal  corpuscle        \  1 

——  *  T         i 

Capillaries  of  the  cortical  labyrinth 
Capillaries  of  the  glomcruli  ^ 

/ 


Efferent  vessel  from  renal  corpuscle 


444 


THE  URINARY  SYSTEM 


The  venulse  recta?  are  peculiar  in  their  typically  straight  course, 
and  in  the  fact  that  the  cells  of  their  endothelium  are  extremely  long — - 
so  long  indeed,  as  frequently  to  present  a  somewhat  fibrous  appearance, 
the  elongated  axis  of  the  cell  heing  parallel  to  the  long  axis  of  the  vessel. 
The  capsule  of  the  kidney  is  supplied  by  branches  of  the  lumbar, 
phrenic,  and  suprarenal  arteries,  which  form  a  rich,  capillary  plexus. 
These  vessels  anastomose  with  the  terminal 
branches  of  the  interlobular  arteries  of  the 
kidney  in  the  manner  above  described — a 
fact  which  acquires  surgical  importance  from 
its  relation  to  the  establishment  of  a  collat- 
eral circulation. 

The  table  on  page  443  may  be  useful  as  a 
resume  of  the  more  important  paths  in  the 
course  of  the  renal  circulation,  in  it  the 
names  of  the  several  vessels  are  arranged  in 
order  and  the  arro\vs  indicate  the  direction 
of  the  blood  current. 

Lymphatics.— The  renal  lymphatics  con- 
sist of  a  superficial  set  which  forms  plexuses 
in  the  perirenal  fat  and  deeper  layers  of  the 
capsule,  and  a  deep  set  which  supplies  the 
parenchyma  of  the  organ.  These  two  sets  of 
lymphatic  vessels  are  in  communication  by 
frequent  anastomoses.  The  vessels  of  the 
superficial  set  convey  their  lymph  to  the 
neighboring  lymph  glands  of  the  lumbar 
region. 

The  deep  renal  lymphatics  accompany 
the  arteries  and  veins  throughout  their 
course.  They  form  narrow  cleftlike  vessels 

of  irregular  caliber  in  the  scanty  interstitial  tissue  between  the  urinifer- 
ous  tubules  of  both  cortex  and  medulla.  These  vessels  are  relatively  few 
in  number.  They  converge  to  the  hilum  of  the  organ  where  they  pass  to 
the  nearby  lymphatic  glands. 

Nerves. — The  nerves  of  the  kidney  include  both  medullated  and 
non-medullated  fibers.  The  sympathetic  fibers  form  a  ganglionated 
plexus  in  the  connective  tissue  about  the  renal  pelvis.  From  this  plexus 
fibers  are  distributed  to  the  blood-vessels  of  the  capsule  and  to  the 
parenchyma  of  the  organ.  The  latter  accompany  the  blood-vessels,  dis- 


Fio.  409. — NERVE  ENDINGS 
IN  A  CONVOLUTED  TUBULE 
OF  THE  FROG'S  KIDNEY. 

a,  nerve  fiber;  b,  blood-ves- 
sel; c,  secreting  epithelium. 
Methylene  blue;  cochineal. 
Very  highly  magnified.  (Af- 
ter von  Smirnow.) 


EENAL  PELVIS  AND  UEETERS  445 

tributing  their  fibers  to  the  walls  of  the  arteries  and  veins  and  to  the 
uriniferous  tubules  of  both  cortex  and  medulla. 

The  parenchymal  branches  form  an  'epilemmal  plexus'  in  the  in- 
terstitial connective  tissue  about  all  portions  of  the  uriniferous  tubule. 
From  this  plexus  fibrils  pierce  the  membrana  propria  and  anastomose  to 
form  a  'hypolemmal  plexus'  about  the  base  of  the  epithelial  cells.  Ter- 
minal fibrils  penetrate  between  the  epithelial  cells  where  they  form 
minute  end  knobs. 

RENAL  PELVIS  AND  URETERS 

The  excretory  passages  of  the  kidney  include  the  renal  pelvis,  the 
ureters,  the  urinary  bladder  and  the  urethra.  All  of  these  portions 
possess  certain  common  characteristics.  They  have  three  coats,  mucous, 
muscular,  and  fibrous,  and  are  lined  by  a  common  type  of  epithelium, 


FIG.  410. — CAST  OF  THETELVIS,  INFUNDIBTJLA  AND  CALICES  OF  THE  KIDNEYS 

OF  A  MAN. 

Showing  the  expansion  of  the  ureter,  the  subdivision  of  the  pelvis,  and  the  con- 
cave facets  by  which  the  calices  fit  over  the  apices  of  the  renal  pyramids.  (After 
Hauch.) 

transitional,  which  extends  from  the  renal  pelvis  to  the  prostatic  por- 
tion of  the  urethra. 

The  mucosa  of  the  renal  pelvis  and  ureter  is  lined  by  transitional 
epithelium  which  rests  upon  a  fibrous  tunica  propria.  The  epithelium 
consists  of  several  cell  layers,  of  which  the  superficial  is  formed  by  broad 


44G 


THE  UKINARY  SYSTEM 


cuboidal  cells,  or  thick  flattened  plates,  whose  form  varies  with  the  state 
of  distention  of  the  organ,  and  whose  deep  surfaces  are  indented  by  the 
rounded  ends  of  the  pear-shaped  cells  which  form  the  deeper  layers.  The 
deepest  cells  are  smaller  and  are  irregularly  spheroidal  in  shape.  They 


FIG.  411.— TRANSECTION  OF  HUMAN  URETER. 
Hematein  and  eosin.     Photo.     X  113. 

are  firmly  attached  to  the  underlying  connective  tissue  which  here  and 
there  projects  into  the  epithelial  layer  carrying  with  it  the  most  super- 
ficial capillary  vessels.  The  cells  of  the  deeper  layers  divide  by  karyo- 
kinesis  and  push  toward  the  surface  to  replace  the  more  superficial  cells 
which  are  gradually  desquamated.  Direct  cell  division  occurs  in  the 


RENAL  PELVIS  AND  URETERS 


44? 


large  plate-like  cells  of  the  superficial  layer.  The  thin  transitional  epi- 
thelium of  the  calyces  is  continuous  with  the  columnar  epithelium  of -the 
papillary  ducts. 

The  tunica  propria,  continuous  with  the  renal  interstitial  tissue, 
contains  both  col- 
lagenous  fibers 
and  elastic  fibers. 
It  is  indistinctly 
divisible  into  a 
superficial  denser 
portion,  and  an 
open-meshed  deep 
portion  whose  fi- 
brous bands  loose- 
ly attach  the  mu- 
cous membrane  to 
the  muscular  coat. 
This  deep  layer  is 
analogous  to  t  h  e 
submucosa  of  the 
alimentary  tract. 
The  mucous  mem- 
brane is  thrown 
into  numerous 
deep  folds  or  ruga? 
which  in  the  ure- 
ter have  a  longi- 
tudinal direction; 
this  condition 
gives  to  the  canal 
in  transverse  sec- 
tion a  stellate  ap- 
pearance. Irregu- 
lar folds  or  inva- 
ginations  of  the 
epithelium  occur 
in  the  renal  pelvis 

and  have  been  described  as  glands,  but  true  secreting  glands  are  not 
found.  Occasional  lymphocytes  occur  in  the  mucosa,  and  small  lymph 
nodules  have  also  been  found  but  cannot  be  regarded  as  of  constant 


FIG.  412. — TRANSITIONAL  EPITHELIUM  OF  DOG'S  URETER. 

A,  in  the  contracted  condition;  B,  in  the  distended  con- 
dition; o,  basal  layer  of  cubic  cells;  b,  middle  layer  of  polyg- 
onal cells;  c,  superficial  layer  of  rectangular  and  ovoid 
cells.  (R.  W.  Harvey,  Anat.  Rec.,  3,  5,  1909.)  X  750. 


448  THE  URINARY  SYSTEM 

occurrence.  The  mucosa  becomes  gradually  thinner  as  it  is  traced 
through  the  infundibula  and  calyces  and  is  reflected  upon  the  surface 
of  the  renal  pyramids. 

The  muscular  coat  of  the  ureter  consists  of  a  well-defined  layer 
of  circular  fibers  within  which  are  many  discrete  bundles  of  longitudinal, 
smooth  muscle.  In  the  lower  half  of  the  ureter  a  third  layer,  whose 
fibers  also  have  a  longitudinal  direction,  is  found  outside  the  circular 
fibers.  In  this  portion  of  the  ureter,  therefore,  the  muscular  coat 
consists  of  three  layers,  an  inner  longitudinal,  middle  circular,  and 
outer  longitudinal. 

In  the  renal  pelvis  and  calyces  the  muscular  coat  becomes  pro- 
gressively thinner  toward  the  renal  substance,  and  at  the  apex  of  the 
pyramid  consists  chiefly  of  circular  fibers  which  are  slightly  thickened 
to  form  a  'sphincter'  about  the  papilla. 

The  outer  fibrous  coat  of  the  ureter  consists  of  areolar  tissue  which 
blends  with  that  of  the  surrounding  parts.  In  the  renal  pelvis  this 
coat  becomes  continuous  with  the  connective  tissue  capsule  of  the  kidney. 
(For  development  of  excretory  passages,  see  next  Chapter.) 

Blood  Supply. — The  larger  blood-vessels  lie  in  the  outer  fibrous 
coat  and  distribute  branches  to  the  muscular  coat  and  to  the  mucous 
membrane.  In  the  latter  they  form  a  superficial  capillary  plexus  which 
is  in  unusually  intimate  relation  with  the  deeper  cells  of  the  lining 
epithelium. 

The  Lymphatics. — The  lymphatics  begin  in  an  intramuscular  plexus 
and,  by  scanty  vessels,  in  the  deeper  part  of  the  mucosa.  They  pass 
to  larger  vessels  in  the  outer  coat,  which  possess  valves,  and  convey 
the  lymph  to  the  neighboring  lymph  nodes. 

The  Nerves. — The  nerves  form  a  coarse  plexus  in  the  outer  fibrous 
coat  which  contains  many  small  ganglia.  From  this  plexus  motor 
fibers  are  distributed  to  the  muscular  layers,  and  sensory  fibers  to 
the  mucosa.  The  latter  form  a  plexus  beneath  the  epithelium  from 
which  terminal  fibers  pass  to  end  by  minute  end  brushes  in  the  con- 
nective tissue  and  by  varicose  fibrils  between  the  deep  -cells  of  the  epi- 
thelium. 

THE  URINARY  BLADDER 

The  wall  of  the  urinary  bladder  closely  resembles  that  of  the  ureter. 
It  consists  of  mucous,  muscular,  and  fibro-serous  coats.  Its  mucous 
membrane  is  lined  by  transitional  epithelium  like  that  of  the  ureter 


THE  URINARY  BLADDER 


449 


and  renal  pelvis.  It  is  therefore  impossible  to  determine  from  which 
of  these  portions  detached  epithelial  cells  are  derived  when  found  by 
microscopical  examination  of  the  urine.  Epithelium  may  become  de- 


FIG.  413. — TRANSVERSE  SECTION  OF  URINARY  BLADDER  OF  DOG. 
a,  b  and  c,  compose  the  tunica  mucosa;  d,  e  and/,  the  tunica  muscularis;  g,  tunica 
serosa;  a,  transitional  epithelium;  b,  lamina  propria  mucosse;  c,  deep  portion  ol 
tunica  mucosa,  corresponding  to  a  tela  submucosa;  d,  internal  longitudinal  muscle 
layer;  e,  middle  circular  muscle  layer;  /,  external  longitudinal  muscle  layer.  The 
tunica  mucosa  is  thrown  into  larger  and  smaller  folds.  X  20. 

tached  from  any  portion  of  the  excretory  passages,  and  as  a  result  of 
inflammatory  changes  not  only  the  superficial  cells  but  also  the  deeper 
pear-shaped  cells  may  be  desquamated. 

The  character  of  the  epithelium  varies  with  the  collapse  and  dis- 
tcntion  of  the  organ.     When  empty  the  mucous  membrane  is  thrown 


450 


THE  UEINAEY  SYSTEM 


into  deep  folds  or  rugae,  whose  surface  also  presents  secondary  folds 
of  irregular  direction.  The  epithelial  layer  is  relatively  thick,  and  is 
thicker  on  the  sides  of  the  folds  than  upon  either  their  apices  or  bases 
where  the  folding  of  the  epithelium  increases  the  tension  of  its  cells. 
When  the  organ  is  distended,  the  folds  are  more  or  less  completely 
obliterated,  the  epithelial  layer  is  much  thinned,  often  until  it  appears 


FIG.  414. — THE  MUCOSA  OF  A  CHILD'S  BLADDER  IN  THE  CONTRACTED  STATE  OF  THE 

ORGAN. 

a-a,  and  a'-a',  transitional  epithelium;  b,  fibro muscular  tissue  of  the  mucosa. 
Hematein  and  eosin.    Photo.     X  216. 

to  consist  of  no  more  than  a  double  layer  of  cells,  and  its  cells  be- 
come much  broader  and  relatively  much  thinner  than  in  the  collapsed 
or  empty  condition.  Hence  the  transitional  variety  of  epithelium,  by 
which  the  organ  is  lined,  may  be  said  to  be  remarkable  for  the  extreme 
elasticity  of  its  cells. 

The  mucous  membrane,  except  near  the  urethral  orifice,  contains 
no  glands.  In  this  location,  however,  the  bladder  of  adult  man  contains 
a  few  small  mucus-secreting  glands,  lined  by  columnar  cells  (K61- 


THE  UEINABY  BLADDER 


451 


liker).     These  are  not  present  in  infancy.    They  have  been  interpreted 
as  vestigial  prostatic  tubules. 

The  tunica  propria  resembles  that  of  the  ureter  and  is  loosely  united 
to  the  muscular  coat.  This  latter  layer  is  formed  by  interlacing 
bundles  of  'smooth  muscle.  It  varies  much  in  thickness  according  to 
the  condition  of  the  organ,  being  relatively  thick  when  the  viscus  is 


FIG.  415. — TRANSITIONAL  EPITHELIUM  OF  DOG'S  BLADDER. 

A,  in  the  contracted  condition;  B,  in  the  distended  condition.    (R.  W.  Harvey, 
Anat.  Rec.,  3,  5,  1909.) 


empty  and  very  thin  when  it  is  completely  distended.  In  most  portions 
three  indistinct  layers  can  be  observed,  a  middle  thick  layer  of  circular 
fibers,  and  an  inner  and  outer  longitudinal  layer.  The  outer  longitudinal 
muscle  is  most  distinct  on  the  anterior  and  posterior  surfaces  of  the 
organ. 

The  outermost  coat  of  the  bladder  consists  of  areolar  tissue,  having 
very  broad  meshes ;  in  the  lower  portion  of  the  bladder  this  coat  blends 
with  the  connective  tissue  of  the  adjacent  organs.  Over  the  fundus  of 


452 


THE  URINARY  SYSTEM 


the  organ  its  outer  fibrous  coat  is  covered  by  the  peritoneum,  the  con- 
nective tissue  of  which  is  indistinguishable  from  that  of  the  outer  coat 
of  the  bladder ;  it  is  clothed  by  the  peritoneal  mesothelium. 

Vascular  and  Nerve  Supply.— The  vascular  and  nerve  supply  of 
the  bladder  is  exactly  similar  to  that  of  the  ureter.     The  larger  blood- 


FIG.  416. — EPITHELIAL  CELLS  FROM  THE  BLADDER  OF  THE  RABBIT. 

A,  as  seen  from  the  under  surface,  showing  the  depressions  made  by  the  under- 
lying polygonal  and  pyriform  cells  (P);  B,  side  view  of  similar  cell.  (After  Klein, 
from  Schafer.) 

vessels  occur  in  the  outer  fibrous  coat,  whence  they  distribute  branches 
to  the  muscular  coat  and  mucous  membrane.  Many  small  ganglia  are 
also  found  in  the  outer  coat,  and  motor  and  sensory  nerves  are  dis- 
tributed to  the  musculature  and  to  the  epithelium  and  connective  tissue 
of  the  mucosa,  as  in  the  ureter. 


THE  URETHRA 


THE  FEMALE  URETHRA 

The  mucosa  of  the  female  urethra  is  lined  by  a  variable  type  of 
epithelium.  Being  continuous  with  the  mucosa  of  the  bladder,  the 
epithelium  of  the  urethra  is  at  first  of  the  transitional  variety,  but  as 
it  approaches  the  meatus  this  is  changed  to  a  stratified  squamous 
type  which  is  continuous  with  that  of  the  vestibule.  In  certain  indi- 
viduals the  superficial  cells  of  the  midportion  of  the  urethra  are  much 
elongated  and  assume  an  irregular  stratified  columnar  type. 

The  epithelium  rests  upon  a  tunica  propria  of  dense  areolar  con- 
nective tissue  whose  outer  portion  blends  with  a  looser  connective 


THE  UKETHEA 


453 


tissue  which  contains  many  broad  venous  channels  and  forms  a  sort 
of  spongy  erectile  tissue.  This  erectile  coat  is  surrounded  by  a  thin 
muscular  coat  whose  innermost  fibers,  longitudinal  in  direction,  are 
continued  outward  to  the  meatus,  and  whose  outer  circular  fibers,  de- 


' 


FIG.  417. — TRANSECTION  OF  THE  FEMALE  URETHRA. 

d,  gland-like  diverticulum ;  e,  urethral  epithelium;  L,  urethral  lumen;  m,  striated 
fibers  of  the  urethral  muscle;  s,  erectile  tissue  of  the  tunica  propria,  containing 
many  venous  spaces  and  smooth  muscle  fibers.  X  10.  (After  Kolliker.) 

ficient  toward  the  meatus,  are  often  slightly  thickened  near  the  neck 
of  the  bladder  to  form  an  indistinct  sphincter  urethra  muscle.  This 
coat  contains  occasional  striated  muscle  fibers.  The  female  urethra 
is  scantily  supplied  with  urethral  glands  which  open  near  the  meatus 
and  supply  a  meager  mucoid  secretion. 


454  THE  URINARY  SYSTEM 

THE  MALE  URETHRA 

The  male  urethra  conducts  the  urine  from  the  bladder  to  the  sur- 
face, its  course  being  through  the  axis  of  the  corpus  spongiosum  of  the 
penis  (Fig.  446).  It  forms  the  terminal  segment  also  of  the  genital 
canal  and  conducts  the  semen;  it  accordingly  performs  a  double  func- 
tion, serving  both  the  urinary  and  the  male  reproductive  system.  The 
character  of  its  epithelium  is  variable,  not  only  in  its  successive  por- 
tions, but  it  is  also  subject  to  great  individual  variation,  and  like  that 
of  the  bladder  and  ureter  changes  its  appearance  according  as  the  canal 
is  collapsed  or  distended.  In  the  first  or  prostatic  portion  of  the  urethra 
the  epithelium  is  of  the  transitional  type ;  in  the  membranous  and  penile 
portion  its  superficial  cells  are  elongated  so  that  the  epithelium  usually 
acquires  a  stratified  columnar  form;  near  the  meatus  the  type  is  again 
exchanged  for  a  stratified  squamous  epithelium  which  is  continuous 
with  that  of  the  glans  penis. 

The  tunica  propria  of  the  urethra  consists  of  areolar  tissue  in  which 
are  embedded  the  small  branched  tubulo-acinar  urethral  glands  (of 
Littre)  lined  by  columnar,  mucus-secreting  cells.  These  glands  are 
more  abundant  along  the  upper  surface.  The  mucosa  also  contains 
frequent  lacunar  imaginations  of  the  epithelium,  and  is  thrown  into 
longitudinal  rugae,  its  lumen  being  obliterated  except  when  distended 
by  the  passage  of  urine. 

The  tunica  propria,  and  especially  that  portion  which  is  distant  from 
the  urethral  canal,  is  permeated  by  the  thin-walled  broad  venous  spaces 
of  the  erectile  tissue  of  the  corpus  spongiosum.  The  septa  between 
these  venous  spaces,  in  addition  to  the  dense  areolar  tissue  of  which 
they  chiefly  consist,  contain  many  bundles  of  longitudinal  smooth 
muscle.  In  the  deeper  portions  of  the  urethra  circular  muscle  fibers 
are  also  found  in  the  outer  part  of  this  coat,  and  near  the  orifice  of 
the  bladder  they  are  somewhat  thickened  to  form  the  sphincter  urethras 
Moreover,  the  corpus  spongiosum  is  invested  with  a  thick  sheath  of 
dense  fibrous  connective  tissue.  At  the  apex  of  the  prostate  circularly 
disposed  striped  muscle  fibers  form  a  second  urethral  sphincter,  the 
external  vesical  sphincter. 

Nerve  Supply. — The  nerve  supply  of  the  urethra  includes  both 
sensory  and  motor  spinal  fibers,  and  sympathetic  fibers  for  the  smooth 
muscle  and  the  blood-vessels. 


CHAPTER   XV 
THE   EEPRODUCTIVE   SYSTEM 

GENERAL  CONSIDERATIONS 

The  reproductive  system  differs  structurally,  widely  in  the  two 
The  several  organs  involved,  however,  are  in  general  strictly 
homologous  in  the  male  and  female  organism.  The  differences  result 
from  a  divergent  specialization  concomitant  with  a  division  of  lahor 
in  the  reproductive  act  and  process.  The  specialization  involves  both 
progressive  and  regressive  differentiation,  the  latter  producing  certain 


Sinus  prostaticus 


Prepuce 
Clans  penis 

Fossa  namcularis 


Ampulla  of  ductus  defer  ens 

Seminal  vesicle 
Ejaculatory  duct 
Prostate  gland 

turethral  gland 
Btilbus  urethrae 
Ductus  deferens 

Paradidymis 
Ductuli  efferentes 
Ductulus  abberans 
Ductus  epididymis 

Rete  testis 
Tubuli  recti 


*Tubuli  contorti 
A  ppendix  epididymis 

FIG.  418. — DIAGRAM  OF  MALE  GENITALIA.     (Adapted  from  Merkel.) 

vestigial    appendages,  of  different  origin  in  the  opposite  sexes.     The 
MALI:  OIIGAXS  OF  UKI-KOIHTTION  include  a  primarily  and  essentially  in- 
ternal group  of  genital  organs,  namely,  the  testis,  and  its  associated 
29  455 


456 


THE    REPRODUCTIVE    SYSTEM 


ducts,  glands  and  appendages;  and  an  external  genital  organ,  the  penis 
(Fig.  418.)  The  FEMALE  ORGANS  OF  REPRODUCTION'  likewise  include  an 
internal  group  of  aemial'ia,  namely,  the  ovary,  with  its  ducts  and  the 


Hydatid  of  Murgagni 


FIG.  419.— DIAGRAM  OF  FEMALE  INTERNAL  GKNITALIA. 

« 
associated  glands  and  appendages;  and  a  group  of  external  genitalia 

and  glands  (Fig.  419).    The  essential  sex  organs  are  the  testis  and  ovary, 
respectively. 


DEVELOPMENT 

The  primary  anlages  are  the  same  in  both  sexes.  They  include  essen- 
tially: a  pair  of  undifferentiated  sex-glands  or  gonads  located  on  the  mid- 
ventromesial  side  of  each  fetal  kidney  (Wolffian  body  or  mesonephros) ;  a 
double  pair  of  parallel  canals,  the  fetal  Wolffian  (mesonephric)  ducts  and 
the  Hiillerian  ducts.  An  embryo  at  this  stage  of  development  (13  milli- 
meters, Fig.  210,  about  40  days)  is  said  to  be  in  the  indifferent  sexual  stage. 
The  ducts  communicate  terminally  with  the  gonads  and  the  exterior.  Sub- 
sequently they  undergo  a  different  development,  as  do  also  the  terminal 
associates  (gonads,  and  urogenital  sinus,  respectively)  in  the  two  sexes. 
For  the  details  of  this  process  reference  must  be  made  to  a  text-book  of 
Embryology.  But  briefly,  the  primitive  gonads  in  the  female  develop  into 
the  ovaries,  in  the  male  into  the  testes.  In  the  female  the  Miillerian  ducts 
become  the  oviducts,  and  fuse  proximally  to  form  the  uterus  and  vagina; 
in  the  male,  this  duct  suffers  regressive  changes  and  persists  only  as  ves- 
tiges :  the  appendix  testis,  and  the  sinus  pocularis.  On  the  contrary  the 
Wolffian  duct  becomes  vestigial  in  the  female,  persisting  as  the  appendix 
fimbria  (hydatid  of  Morgagni)  and  the  canal  of  Gartner;  while  in  the  male, 
it  develops  into  the  main  portion  of  the  definitive  duct  system :  ductus  epi- 
didymis,  and  ductus  deferens.  The  tubules  of  the  fetal  kidney  (Wolffian 


DEVELOPMENT 


457 


body)  also  contribute  to  the  excretory  duct  system.  In  the  male,  they  per- 
sist in  part  (10  to  15)  to  form  the  ductuli  efferentes;  several  may  become 
vestigial  forming  thus  the  ductuli  aberrentes,  the  paradidymis  and  the 
appendix  epididymis.  In  the  female,  these  ducts  early  disappear  for  the 


Inguinal  ligament 

Mesonephric  due 
MuUerian  duct 


--Apex  of  bladder 
Bladder 


Opening  of  ureter 


(  Opening  of  mesoneph- 

\     ric  duct 

(  Opening  of  MuUerian 

\     duct 
Rectum 

Urogenital  sinus 
Cloaca 

Genital  tubercle 
Genital  ridge 
Opening  of  cloaca 


FIG.  420. — DIAGRAMS  ILLUSTRATING  THE  METAMORPHOSES  OF  THE  INDIFFERENT 
(A)  UROGENITAL  SYSTEM  INTO  THE  MALE  (B),  AND  FEMALE  (C)  SYSTEMS.  (From 
Polak,  after  Hertwig.) 

most  part — a  variable  number  persisting  as  vestigial  structures:  the  epo- 
ophoron  and  the  parob'phoron. 

The  seminiferous  tubules  (including  the  recti  and  rete  tubuli)  of  the 
testis  arise  as  solid  cords  of  cells  continuous  with  the  peritoneal  epithelial 
covering  of  the  gonad,  and  apparently  as  derivatives  of  this  so-called  'ger- 
minal epithelium.'  These  cords  subsequently  acquire  a  lumen,  and  connect 
with  the  efferent  tubules.  In  the  ovary  likewise  such  cell  cords  (sex-cords) 
appear,  continuous  with  the  peritoneal  (germinal)  epithelium;  from  these 
develop  the  ovarian  follicles  with  their  ova,  as  will  be  described  below. 
The  relation  of  the  extra-regional  'primordial  germ-cells'  to  the  germinal 
epithelium  and  to  sex-gland  derivatives,  discussed  in  the  next  section, 


Kidney" — -- 

Appendage  of  testicle  \ 
Hydatid  of  Morgagni J 


Epididym 

Testis 

Paradidymis 
Deferent  duct 


-Apex  of  bladder 


ig  of  ureter 

Urethra 

(  Opening  of  ejacul 

\     duct 
Prostate 


f 
Seminal  vesicle  r Jf.  - 

Deferent  duct  * •// 


--Apex  of  bladder 


Round  ligament 


Vagina 


DEVELOPMENT 


459 


remains  in  doubt.  Felix  (Keibel  and  Mall's  "Human  Embryology,"  vol.  2) 
inclines  to  the  view  that  in  man  the  primordial  germ-cells  (primitive  geni- 
tal cells)  disappear,  and  that  they  bear  no  genetic  relationship  to  the  primi- 
tive germ-cells  (secondary  genital  cells)  of  the  gonad. 

Table  of  the  Adult  Male  and  Female  Derivatives  of  the  Fetal 
(Indifferent)  Reproductive  System. 

(The  vestigial  structures  are  given  in  italics,  synonyms  in  parentheses.) 
INTERNAL  GENITALS. 


Indifferent  stage. 

Male. 

Female. 

Genital  ridge. 

Testis. 
Gubernaculum      (mesor- 
chium)  . 

Fimbria  ovarica. 
Ovary 
Ovarian   ligament    (meso- 
varium). 
Round  ligament. 

Wolffian     body     (tubules) 
(Mesonephros). 

Globus  major  of  epididy- 
mis    (ductuli     efferen- 
tes). 
Paradidymis. 
Ductuli  aberrenles. 
Appendix   of  epididymis 
(stalked  hydatid). 

Epoophoron    (Parovarium, 
organ  of  Rosenmuller)  . 

Paroophoron. 

Wolffian  duct  (Mesonephric 
duct). 

Duct  and  globus  minor 
of  epididymis. 
Ductus  deferens. 
Seminal  vesicle. 
Ejaculatory  duct. 

Chief  vesicular  appendage 
(Hydatid  of  Morgagni)  . 
Collecting    tubule    of   epo- 
ophoron. 
Canal  of  Gartner. 

Mullerian  duct. 

Appendix    lestis     (sessile 
hydatid). 
Sinus  pocularis  (Uterus  or 
vagina    masculina,    or 
utriculus  prostalicus)  . 

Oviducts  (Uterine  or  Fal- 
lopian tubes). 
Uterus. 
Vagina. 

EXTERNAL  GENITALS. 


Urogenital  sinus. 

Genital  tubercle. 
Genital  folds. 
Genital  swellings. 

[Prostatic  and  membra-] 
nous  portions  of  male  ^ 
[     urethra. 
Penis. 

Scrotum. 

Urethra. 
Vestibule. 

Clitoris. 
Labia  minora. 
Labia  majora. 

460  THE  REPRODUCTIVE  SYSTEM 

The  outline  on  the  preceding  page  summarizes  in  tabular  form  the 
main  facts  regarding  the  development  of  the  reproductive  system. 

In  both  sexes  the  Wolffian  duct  proximally  sprouts  a  duct  which  dilates 
and  subdivides  distally,  meanwhile  separating  from  the  parent  duct  and 
making  a  secondary  connection  with  the  developing  bladder.  The  subdi- 
visions elongate  to  form  the  collecting  portion  of  uriniferous  tubules,  and 
unite  with  ontogenetically  distinct  tubules  (the  secretory  portions)  to  form 
the  complete  tubules.  The  dilatation  and  earlier  subdivisions  become  the 
pelvis  and  calyces,  and  the  proximal  portion  of  the  original  anlage  persists 
as  the  ureter. 

GAMETOGENESIS 

The  study  of  the  sex  or  genital  glands,  the  ovary  and  the  testis, 
is  perhaps  best  approached  by  way  of  a  consideration  of  the  mechanism 
by  which  they  perform  their  respective  specific  functions,  namely  the 
production  of  ova  and  spermatozoa  ripe  for  union.  The  common  process 
is  known  as  gametogenesis.  The  end  products  are  the  male  and  female 
gametes,  or  sperm  and  ova.  In  the  male  the  process  is  known  as 
spermato genesis,  in  the  female,  oogenesis.  The  act  of  subsequent  union 
.of  the  gametes  is  called  fertilization,  and  the  fertilized  egg  is  the  zygote. 

The  result  of  gametogenesis  is  the  preparation  of  a  primary  germ- 
cell  for  union  with  a  gamete  from  the  opposite  sex.  The  essence  of 
the  process  is  known  as  maturation,  and  involves  prominently  mitotic 
cell  division.  However,  the  method  of  division  is  not  of  the  simple 
homeotypic  type,  where  a  chromosome  simply  divides  longitudinally  into 
two  daughter  chromosomes,  but  is  of  the  type  called  lieterotypic,  the 
chief  characteristic  of  which  is  the  formation  of  tetrads.  The  latter 
are  of  various  sorts,  all,  however,  characterized  by  a  four-lobed  condition 
representing  a  quadripartite  double  or  bivalent  chromosome  (Plate  B, 
figs.  15-18,  page  467). 

Both  sperm  and  egg  trace  their  ancestry  back  to  primordial  germ 
cells,  indistinguishable  in  the  sexually  undifferentiated  organism,  ex- 
cept for  a  difference  in  chromosome  content,  which  difference  is  com- 
monly indiscernible.  In  certain  instances,  e.g.,  Ascaris,  the  germ  cell 
can  be  distinguished  from  the  soma  cell  at  the  two-cell  stage.  In  a 
number  of  vertebrates,  e.g.,  dogfish,  turtle,  etc.  (Allen),  the  primordial 
germ-cell  has  been  traced  from  a  position  among  the  entoderm  cells 
lining  the  gut  of  the  young  embryo  through  a  migration  into  the  dif- 
ferentiating gonad,  ovary  or  testis.  Swift  (Amer.  Jour.  Anat.,  15,  4, 


GAMETOGENESIS  461 

1914)  has  traced  the  primordial  germ-cells  in  the  chick  from  a  crescen- 
tic  area  in  the  entoderm  in  front  of  the  head  end  of  the  primitive  streak, 
through  their  migration  to  the  gonad  by  way  of  the  developing  blood- 
vessels. The  earlier  anatomists,  on  the  other  hand,  derived  the 
primordial  germ-cells  from  the  mesothelial  covering  (germinal  epi- 
thelium) of  the  germ  gland  region  of  the  primitive  kidneys,  the  meso-1 
nephroi.  This  mode  of  origin,  either  exclusively  or  in  part,  is  still 
supported  by  certain  investigators. 

Whatever  the  actual  source  of  origin — whether  entodermal  or  meso- 
dermal,  whether  specific  or  otherwise — and  whenever  the  time  of  dif- 
ferentiation, whether  early  or  relatively  late,  the  primordial  germ-cells 
in  the  gonad  undergo  extensive  proliferation,  increasing  greatly  in 
numbers.  The  earlier  generations  may  be  inclusively  designated  pri- 
mary spermatogonia  or  oogonia  respectively,  the  final  generation  taking 
the  term  secondary  gonia.  The  question  of  the  origin  of  the  primordial 
germ-cells  bears  upon  the  hypothesis  of  the  continuity  of  germ-plasm. 

Spermatogenesis. — Since  gamete  production  is  easier  to  follow, 
though  apparently  more  specialized,  in  the  male,  spermatogenesis  is 
advantageously  first  described.  For  the  purpose  we  may  employ  the 
active  testis  of  Schistocerca  damnified,  a  common  grasshopper.  Grass- 
hopper material  of  many  species  is  peculiarly  favorable  for  a  demon- 
stration of  the  process  of  spermatogenesis.  This  scheme  will  apply 
with  slight  qualification  to  most  grasshoppers.  The  reduced  number 
of  chromosomes  is  the  same,  namely,  12 ;  moreover,  this  material  shows 
peculiarly  well  the  accessory  or  sex  chromosome,  and  thus  serves  as 
a  splendid  basis  for  a  discussion  and  comprehension  of  the  salient  facts 
and  recent  theories  touching  the  problems  of  the  determination,  control, 
and  inheritance  of  sex. 

The  grasshopper  testis  is  a  long  tubular  structure  subdivided  into 
a  number  of  compartments,  or  cysts,  each  filled  with  cells  of  ap- 
proximately the  same  stage  of  development,  the  successive  stages  in 
spermatogenesis  being  represented  in  successive  cysts  from  distal  to 
proximal  pole.  For  purpose  of  readiest  study  there  is  required,  then,  a 
median  longitudinal  section  of  an  entire  testis  in  active  condition.  As 
is  obvious,  such  material  is  useful  also  for  illustrating  mitosis  but,  with 
the  exception  of  the  spermatogonial  and  second  maturation  mitoses, 
cannot  be  regarded  as  typical;  but  for  application  and  extension  of  a 
preliminary  knowledge  of  simple  mitosis  it  is  perhaps  unexcelled.  It 
must  be  emphasized  that  this  peculiar  type  of  cell  division,  charac- 
terized chiefly  by  the  phenomena  of  synapsis  and  tetrad  formation,  in- 


GAMETOGENESIS  463 

volving  a  reduction  as  well  as  an  ordinary  equation  division,  is  limited 
to  the  maturation  mitoses  occurring  in  active  testes  and  ovaries.  The 
appended  scheme  Avill  serve  to  show  graphically  the  steps  in  spermato- 
genesis  arid  oogenesis,  and  the  correspondences  and  differences  between 
the  two. 

We  may  begin  the  detailed  description  with  the  last  generation  of 
spermatogonia,,  the  secondary  spermatogonia.  In  the  early  resting  stage 
the  nucleus  is  poly -vesicular,  each  vesicle  representing  one  or  several 
chromosomes  (Plate  A,  Fig.  1).  Subsequently  the  separate  vesicles  fuse 
to  form  a  greatly  lobulated  nucleus.  In  Fig.  2  one  vesicle  is  shown  still 
separated ;  this  probably  represents  the  accessory  or  sex  chromosome ;  sub- 
sequently it  also  fuses  with  the  main  nucleus  and  remains  generally 
indistinguishable  from  the  other  nuclear  elements  until  early  stages 
of  the  succeeding  generation  of  cells,  the  primary  spermatocytes  (Fig. 
8).  Figs.  3,  4,  5,  6  and  7  represent  successive  stages  in  the  karyo- 
kinetic  division  of  the  secondary  spermatogonia.  In  the  telophase  of 
the  spermatogonial  division  and  the  earliest  prophase  of  the  primary 
spermatocytes,  as  well  as  subsequently,  the  sex  chromosome  (allosome; 
heterochromosome)  does  not  pass  through  the  diffuse  and  spireme  phases 
of  the  ordinary  chromosomes  (autosomes;  euchromosomes)  but  remains 
chromatic  and  relatively  compact.  Subsequently  it  condenses  consid- 
erably more  (Fig.  8)  and  thereafter  persists  until  late  spermatid  stages 
as  a  compact,  deeply  chromatic  body,  generally  of  oval  or  bilobed  form, 
and  usually  close  to  or  on  the  nuclear  wall  (Figs.  10 ;  plate  B,  14  and  20 ; 
and  plate  C,  27).  Following  the  early  growth  stages,  when  the  nucleus 
is  in  the  resting  or  diffusive  chromatic  stage  (Fig.  8),  a  series  of 
changes  occur  known  as  synapsis.  The  most  characteristic  phase  is  the 
one  in  which  the  spireme  becomes  closely  aggregated  and  polarized 
(synizesis)  and  s  -.hsequently  segmented,  the  segments  becoming  looped 
and  attached  by  their  open  ends  to  the  nuclear  wall  over  a  constricted 
area,  generally  in  the  vicinity  of  the  sex  chromosome.  The  loops  now 
free  one  attached  end  and  unite  in  pairs  by  their  free  ends  forming 
taller  loops,  oriented  similarly  to  the  smaller  loops  (bouquet  figure, 
synaptenic  nucleus).  The  number  of  loops  is  now  half  the  original 
number,  which  represented  the  full  number  of  chromosomes.  This 
chromosome  pairing  is  the  essence  of  synapsis.  An  end  to  end  union 
as  here  described  is  termed  telosynapsis  (metasyndesis) ;  side  by  side 
union,  described  in  certain  forms,  parasynapsis  (parasyndesis).  The 
important  point  is  the  reduction  to  half  (plus  one,  the  accessory)  the 
original  number  (diploid)  of  chromosomes;  the  reduced  number  is 


464 


THE  REPRODUCTIVE  SYSTEM 


termed  the  haploid  group.     The  loops  now  lose  their  polarized  condi- 
tion (postsynaptic  phase)  and  become  scattered  throughout  the  nucleus, 
which  has  meanwhile  grown  in  size,  and  become  more  or  less  closely 
united  into  a  more  or  less  continuous  thread.    This  soon  shows  evidences 
of  a  longitudinal   split    (Fig.    12),   the   diplotene  phase;  subsequently 
this  undergoes  transverse  segmentation  into  half  the  original  number 
(23)  of  chromosomes,  irrespective  of  the  ac- 
,, •-•"'•_" ,.  '/^\    /*     cessory;  thus  there  are  11  segments.     The 
'  '*•/         nucleus  contains  in  addition  a  pale-staining 
plasmosome,  and  the  deep-staining  accessory 
chromosome    in   its    characteristic    location. 
Figs.  11  to  14  are  designed  to  show  these 
two  structures  in  varying  relationships.    Fig. 
15  illustrates  a  late  prophase  condition,  in 
which   the   euchromosomes    (McClung)    are 
less    compact    than,    the    heterochromosome 
(accessory),   and   in   the   typical   tetrad   or 
quadripartite  condition. 

At  this  point  we  may  recapitulate  our 
facts  regarding  the  chromosomes.  The  sper- 
matogonium  contains  23  (Fig.  423  A). 
With  one  exception  the  chromosomes  can  be 
grouped  in  pairs;  such  grouping  gives  11 
pairs.  Moreover,  the  chromosomes  can  be 
arranged  in  a  progressive  series  from  the 
viewpoint  of  size;  the  unpaired,  or  accessory 
chromosome  (10x)  takes  rank  between  the 
9  and  11  chromosomes.  These  chromosomes 
represent  the  original  contribution  from 
father  and  mother  when  the  egg  was  fertilized  preceding  development. 
At  synapsis  the  chromosomes  actually  pair  and  fuse;  and  obviously  in 
the  manner  indicated  in  (A),  for  the  chromosomes  can  again  be  ar- 
ranged in  a  graded  series,  corresponding  approximately  in  size  and  range 
to  the  pairs  indicated.  Since  the  accessory  has  no  mate  the  reduced 
number  of  chromosomes  is  12. 


FIG.  422.— PRIMARY  SPERMA- 
TOCYTE  OF  A  GRASSHOPPER, 
HlPPISCUS  TUBERCULATUS, 
SHOWING  THE  COMPACT 
ACCESSORY  CHROMOSOME 
(x)  AMONG  THE  PALER 
MOSSY  PROPHASE  EUCHRO- 
MOSOMES, AND  THE  IDIO- 

SOME   (i). 

The  cytoplasm  contains 
many  granular  and  filamen- 
tous mitochondria.  Flem- 
ming  fixation;  iron-hematox- 
ylin  stain.  X  1800. 


It  is  now  quite  generally  believed  that  the  chromosomes  of  a  pair  rep- 
resent paternal  and  maternal  contributions;  thus  from  the  viewpoint  of 
inheritance,  assuming  that  the  chromosomes  are  the  vehicles  of  certain 
hereditary  characters  and  qualities,  the  offspring  of  a  pair  of  parents  inherit 


PLATES  A,  B,  AND  C.— SUCCESSIVE  STAGES  IN  THE  SPERMATOGENESIS  OP  SCHISTO- 

CERCA   DAMNIFICA. 

x,  accessory  or  sex  chromosome;  p,  plasmosome;  i,  idiosome.  1  to  7,  spermato- 
gonia;  8  to  19,  primary  spermatocytes;  20  to  26,  secondary  spermatocytes;  27  to  30, 
spermatids,  differentiating  (31  to  35)  into  the  spermatozoon  (36).  10,  synapsis 
stage;  18  and  24,  metaphase  plates  of  chromosomes;  6  a,  diagram  of  a  longitudinally 
split  univalent  chromosome  from  the  metaphase  plate  of  a  spermatozonial  mitosis; 
16b,  diagram  of  a  bivalent  chromosome,  in  tetrad  condition,  from  the  metaphase 
plate  of  the  first  maturation  spindle,  undergoing  the  reduction  division ;  23c,  longi- 
tudinally split  univalent  chromosome  entering  the  second  maturation  spindle  for  the 
equation  division.  (Flemming  fixation;  iron-hematoxylin  stain.)  X  1750. 

465 


PLATE  B. 


13 


14 


, 

20 


15 


18 


21 


19 


S2 


23         24 


PLATES  A,  B,  AND  C. — SUCCESSIVE  STAGES  IN  THE  SPERMATOGENESIS  OF  SCHISTO- 

CEBCA   DAMNIFICA. 

467 


Ofk 

31     32    33   34     36 

PLATES  A,  B,  AND  C.— SUCCESSIVE  STAGES  IN  THE  SPERMATOGENESIS  OF  SCHISTO- 


CERCA   DAMNIFICA. 

469 


PLATE  D. 


/  » 

PLATE  D  (Fics.  1  TO  16). — SUCCESSIVE  STAGES  IN  THE  GROWTH  (1  AND  2,  X  2100, 
AND  3,  X  700),  MATURATION  (4,  5,  6,  7,  8,  9,  10,  11,  12  AND  13,  X  2100,  AND 
14,  X  700),  AND  FERTILIZATION  (15  AND  16,  X  700)  OF  THE  EGG  OF  THE  STAR- 
FISH, Asterias  forbesii. 

In  the  ripe  egg  (3)  the  chromosomes  are  aggregated  in  a  group  connected  with 
the  nucleolus  by  a  chromatic  thread.  In  4  the  nucleolus  is  fragmenting  (c)  and 
the  chromosomes  (a  and  6)  are  taken  onto  the  first  maturation  spindle  (5).  In 
13  two  polar  bodies  are  present,  and  the  female  pronucleus  is  forming.  In  14,  the 
mature  egg,  three  polar  bodies  are  present.  In  15  and  16,  the  male  and  female 
pronuclei  are  fusing  to  contribute  their  chromosomes  to  the  first  segmentation 
spindle. 

30  471 


GAMETOGENESIS 


473 


by  way  of  chromosomes  only  from  their  grandparents.  For  their  parents 
are  simply,  as  it  were,  the  'guardians'  of  their  grandparental  chromosomes 
which,  following  the  synapsis  phase  of  growth  (the  final  stage  of  the  pre- 


FIG.  423. — CHROMOSOME  GROUPS   OF  SCHISTOCERCA   DAMNIFICA. 

(A)  Diploid  chromosome  group  of  dividing  spermatogonium  of  Schistocerca, 
showing  the  11  pairs  of  chromosomes,  and  the  unpaired  (10-x)  accessory  chromo- 
some. (B)  Haploid  group  of  primary  spermatocyte,  showing  11  bivalent  chromo- 
somes and  the  accessory  (10-x).  The  11  bivalents  fall  into  a  series  with  the  same 
size  relationships  as  the  pairs  of  chromosomes  in  the  diploid  group.  (C  and  D) 
Chromosome  groups  of  secondary  spermatocytes,  one  (D)  with  11  univalent 
chromosomes,  like  those  of  the  diploid  pairs,  the  other  (C)  with  similar  chromo- 
somes, plus  the  accessory  (x).  All  mature  eggs  presumably  contain  12  chro- 
mosomes, homologous  with  C. 

vious  fertilization  which  resulted  in  the  parents)  become  redistributed  in 
various  combinations  in  the  maturing  germ  cells  from  which  the  offspring 
develop,  and  determine  their  hereditary  possibilities.  In  other  words  the 
germ-plasm  is  a  continuous  substance  handed  on  from  generation  to  gen- 


474 


THE  REPRODUCTIVE  SYSTEM 


eration.  Its  'elements'  are  the  same,  except  in  so  far  as  the  complement 
is  halved  during  maturation  and  restored  at  fertilization  by  addition  of  an 
equal  quota  from  another  line  of  descent.  This  halving  and  doubling  is 
the  physical  mechanism  which  underlies  the  phenomenon  of  variation  in- 
volved in  heredity.  Offspring  thus  resemble  parents  because  both  have 
had  origin  largely  from  the  same  germ-plasm;  lack  of  resemblance  results 
from  the  fact  mainly  that  the  germ-plasm  of  parents  and  offspring  of  neces- 
sity differ  in  certain  elements  since  different  additions  are  made  at  fertili- 
zation in  the  case  of  successive  generations. 


We  may  now  return  to  the  metaphase  (Fig. 
16)  and  follow  the  further  course  of  the  chromo- 
somes. The  chromosomes  are  in  typical  tetrad 
condition.  The  first  division  most  probably  sep- 
arates the  chromosomes  that  paired  at  synapsis. 
The  unpaired,  odd,  or  accessory  chromosome  (x) 
passes  undivided  and  in  advance  of  the  other 
chromosomes  to  one  pole  of  the  spindle.  Thus 
one  of  the  resulting  daughter-cells,  prespermatid 
or  secondary  spermalocyte,  receives  11  chromo- 
somes, the  other,  11  plus  the  accessory,  or  12 
chromosomes.  Fig.  17  is  a  side  view  and  Fig.  18 
a  polar  view  (metaphase  plate),  of  the  metaphase 
group,  showing  all  12  chromosomes.  The  acces- 
sory is  still  recognizable  at  telophase,  Fig.  19. 
The  chromosomes  of  the  resulting  secondary  sper- 
matocytes  do  not  pass  into  a  diffuse  stage  but  re- 
main more  or  less  compact  and  chromatic — a  con- 
dition characteristic  of  the  later  segmented  spi- 
reme  stage  of  mitosis.  In  half  the  cells  the  acces- 
sory appears  in  its  typical  shape,  staining  reac- 
tion, and  position,  as  shown  in  Fig.  20.  This 
shows  also  a  remnant  of  the  original  spindle. 
Attention  should  here  be  called  to  the  fact  that  in 
many  forms  chromatic  particles  have  been  de- 
scribed passing  from  the  nucleus  into  the  cyto- 


FIG.  424. — DIAGRAMS 
ILLUSTRATING  THE 
BEHAVIOR  OF  THE 
CHROMOSOMES  DUR- 
ING THE  FIRST  (A) 
AND  SECOND  (B) 
MATURATION  Drvi- 


The  bivalent  chro- 
mosome a  +  b  enters 
the  first  maturation 
spindle  and  suffers  a 
reductional  division, 
chromosome  a  being 
separated  from  chro- 
mosome b.  In  the  sec- 
ond maturation  divi- 
sion, each  chromosome 
undergoes  an  ordinary 
longitudinal  division. 
This  division  is  already 
foreshadowed  during 
the  first  or  heterotypic 


division,  producing  the        , 
-.  tetrad  condition  of  the     Plasm'  during  the  growth  stages  of  the  primary 
bivalent  chromosome.       spermatocyte,  particularly  at  the  synapsis  phase. 
Similar    conditions    have    occasionally    been    de- 
scribed also  for  the  spermatogonia,  and  in  several  instances  even  for  the 
secondary  spermatocytes.    These  extrusion  products  are  called  chromidia, 


GAMETOGENESIS  475 

and  are  regarded  by  some  as  the  raw  material  for  mitochondria,  to  which 
latter  certain  investigators  have  attached  hereditary  significance. 

The  further  description  of  specmatogenesis  will  be  confined  to  that 
half  of  the  secondary  spermatocytes  containing  the  accessory  or  sex 
chromosome;  conditions  in  the  other  half  are  closely  similar  except  for 
the  absence  of  the  odd  chromosome.  Figs.  21  and  22  illustrate  suc- 
cessive prophase  stages.  Figs.  23  and  24  illustrate  side  and  polar 
views  of  the  metaphase  of  the  second  maturation  mitosis;  in  the  latter 
all  12  chromosomes  are  shown.  Plate  C,  Figs.  25  and  26  show  anaphase 
and  telophase  stages  respectively.  Fig.  27  is  the  early  spermatid  stage, 
the  accessory  still  conspicuous.  A  conspicuous  cytoplasmic  element  of 
these  stages  is  the  idiozome  (i),  apparently  derived  from  a  portion  of 
the  disappearing  spindle.  Later  stages  of  the  metamorphosis  of  the 
spermatid  are  shown  in  Figs.  28  to  31.  The  idiozome  divides  into  two 
moieties  (Fig.  29).  These  elongate  (Fig.  30)  and  spread  out  over  a 
filament  (Fig.  31),  which  has  grown  out  from  a  dark-staining  granule 
on  the  outer  surface  of  the  nucleus.  The  cytoplasm  also  concurrently 
flows  backward  around  this  filament.  In  conformity  with  what  is 
known  of  a  similar  granule  with  a  similar  function  in  various  forms, 
this  granule  represents  the  centrosome  of  Fig.  23,  but  its  origin  and 
history  are  obscure.  Further  steps  in  the  metamorphosis  are  illustrated 
in  Figs.  32  to  36.  The  mature  spermatozoon  consists  of  a  long,  rela- 
tively lightly  chromatic,  lance-shaped  head,,  a  deeply-staining  thimble- 
shaped  middle  piece  (body),  and  a  long  gradually  tapering  tail.  The 
latter  consists  of  the  central  filament  ensheathed  by  the  products  of 
the  idiozome.  The  entire  spermatozoon  is  furthermore  enveloped  in  a 
close-fitting  sheath  of  cytoplasm.  The  head  originated  from  the  nucleus, 
and  the  middle  piece  presumably  from  the  centrosome  and  a  small 
contribution  of  c}rtoplasm. 

Determination  of  Sex. — Anticipating  somewhat,  we  may  say  that  the 
process  of  oogenesis  is  essentially  similar  to  that  described  for  spermato- 
genesis.  The  cardinal  difference  relates  to  a  numerical  inequality  between 
the  functional  descendants  of  a  spermatogonium  and  an  oogonium:  in  the 
former  case  the  four  resulting  cells  are  all  functional,  and  from  the  stand- 
point of  their  numerical  chromosome  content  of  two  sorts;  in  the  latter, 
three  of  the  resulting  cells  are  abortive  (polocytes),  only  one  remaining 
functional.  Of  the  two  classes  of  spermatozoa,  one  has  an  even  number  of 
chromosomes,  the  other  an  odd  number.  All  mature  eggs  have  the  same 
number  of  chromosomes  as  that  of  the  spermatozoa  with  the  greater  num- 
ber. This  description  applies  strictly  only  to  those  instances  where  an  odd 


476  THE  EEPRODUCTIVE  SYSTEM 

or  accessory  chromosome  appears  in  the  male,  or  where  its  representative 
is  an  odd  group.  Cases  are  known  among  insects,  where  the  homologue  of 
the  accessory  may  have  a  mate  of  smaller  size  (or  possibly  even  equal  size, 
but  of  typical  allosome  behavior — idiochromosomes),  or  where  the  accessory 
representative  may  be  an  even  group,  in  which  instances  the  numerical  rela- 
tionships are  different,  but  the  principle  of  sexual  relationship  remains  the 
same. 

Confining  our  attention  then  to  the  simplest  case,  as  illustrated  in  our 
specimen  of  the  grasshopper,  we  may  note  that  all  the  cells  of  the  female, 
including  the  oogonia,  contain  24  chromosomes.  Two  of  these  correspond 
in  size  to  the  accessory  of  the  male  group,  which  group  in  all  soma  cells 
and  all  spermatogonia  comprises  23  chromosomes.  We  recall  that  one-half 
of  the  spermatozoa  received  11  chromosomes,  the  other  half  11  plus  the 
accessory,  or  12  chromosomes.  All  mature  eggs  contain  12  chromosomes. 
When  therefore  a  spermatozoon  with  11  chromosomes  fertilizes  an  egg  with 
12  chromosomes,  the  resulting  organism  will  have  23  chromosomes,  and 
become  a  male;  when,  on  the  contrary,  a  spermatozoon  with  12  chromo- 
somes fertilizes  an  egg  with  12  chromosomes,  the  organism  will  have  24 
chromosomes  and  become  a  female. 

An  essentially  similar  relationship  is  now  known  to  obtain  in  many 
forms,  chiefly  insects,  but  including  also  various  vertebrates,  even  mam- 
mals and  man.  According  to  Winiwarter  (Arch,  de  Biol.  T.  27,  1912),  the 
white  human  male  produces  spermatozoa  of  two  sorts,  one  with  23  chro- 
mosomes, the  other  with  24 ;  the  male  cells  containing  47  chromosomes,  the 
female  48.  There  is  some  uncertain  evidence  to  indicate  that  the  negro 
has  half  the  number  of  chromosomes  possessed  by  the  white  man,  the 
mulatto  consequently  possessing  numerically  intermediate  groups. 

With  regard  to  the  function  of  the  accessory  chromosome  in  relation 
to  sex  determination,  two  obvious  possibilities  present  themselves:  (1)  it 
may  qualitatively  determine  sex,  that  is,  carry  the  determiner  upon  which 
sex  depends;  (2)  it  may  act  in  a  quantitative  way,  that  is,  sexual  differ- 
ence may  depend  upon  differences  in  the  amount  of  chromatin.  On  the 
contrary  the  presence  of  one  accessory  in  the  male,  arid  two  (homologues) 
in  the  female  may  be  simply  accompaniments  of  sex  in  a  sense  somewhat 
similar  to  secondary  sexual  characters  (e.  g.,  combs  and  spurs  in  poultry), 
these  as  well  as  other  sexual  differences  being  in  common  dependent  upon 
some  more  recondite  fundamental  sex  'determiner/  Experimental  evidence 
tends  increasingly  to  show  that  all  organisms  carry  the  potentialities  of 
both  sexes,  and  that  sex  differences  are  largely  differences  in  degree  of  dif- 
ferentiation;  in  other  words,  that  femaleness  represents  an  inhibited  male. 
The  greater  amount  of  chromatin  in  the  female,  due  to  the  presence  of 
two  sex  chromosomes — as  against  one  in  the  male — may  be  conceived  to 
inhibit  the  higher  grade  of  differentiation  demanded  by  maleness. 

Attempts  have  frequently  been  made  recently  somehow  to  bring  sex 


GAMETOGENESIS  477 

determination  in  line  with  our  knowledge  of  inheritance  in  general,  and 
more  particularly  with  the  principles  of  Mendelian  inheritance.  This  ac- 
cordingly would  seem  to  be  the  logical  place  for  a  brief  presentation  of  the 
main  facts  of  Mcndelism,  and  the  hypothesis  that  attributes  to  the  chromo- 
somes the  function  of  vehicles,  or  determiners  for  hereditary  qualities. 
Barring  the  sexual  numerical  differences  above  discussed,  the  specific  num- 
ber of  chromosomes  is  constant;  that  is,  all  cells  of  the  white  human  male 
have  47,  of  the  female  48  chromosomes.  The  more  variable,  superficial,  or 
more  recently  acquired  characters  are  believed  by  many  to  depend  upon  the 
presence  in  the  developing  egg — consequently  the  cells  of  the  organism — of 
certain  chromosomes,  the  so-called  'determiners.'  The  more  fundamental 
characters  are  believed  to  inhere  in  the  cytoplasm  of  the  egg.  For  exam- 
ple, the  vertebrate  condition  of  a  man  is  thus  believed  to  result  from  the 
constitution  of  the  egg;  the  color  of  his  eyes  from  the  presence  or  absence 
of  some  determiner  or  factor  in  a  particular  chromosome. 

To  elucidate  the  matter  further,  we  must  regard  an  organism  as  a 
congeries  of  almost  numberless  characters;  of  these  some  are  like  those  of 
the  mother  and  her  ancestors,  others  like  those  of  the  father  and  his  an- 
cestors, others  apparent  blends.  In  Mendelian  phraseology  these  characters 
are  called  unit  characters,  and  their  material  basis  is  located  in  particular 
chromosomes.  We  may  select  a  single  pair  of  unit  characters  in  order 
further  to  present  the  principles  of  Mendelian  inheritance.  Suppose  we 
consider  the  coat  color  of  gray  and  white  guinea  pigs.  When  individuals 
characterized  by  these  coat  colors  are  crossed,  the  resulting  offspring,  first 
generation,  are  all  gray  in  color.  The  gray  color  is  said  to  be  dominant, 
the  white  recessive.  However,  the  potentialities  or  determiners  for  white 
coat  color  are  still  present  in  the  gray  hybrid,  for  if  such  hybrids  are  in- 
l  red,  there  result  gray  and  white  offspring  in  the  proportion  of  3  of  the 
former  to  1  of  the  latter.  The  latter  if  inbred  produce  only  white  off- 
spring, hence  called  pure  recessives,  but  of  the  3  gray  only  one  if  bred  with 
its  own  type  (pure  dominants)  will  produce  gray;  two  out  of  the  three  if 
inbred  produce  again  3  gray  to  1  white.  The  proportion  of  1  pure  domi- 
nant to  2  hybrid  dominants  to  1  pure  recessive  is  the  well-known  Mendelian 
formula  for  one  pair  of  unit  characters  in  cross-breeding  of  specific  varie- 
ties. The  character  of  this  formula  depends  upon  the  fact  that  no  germ 
cell  carries  both  determiners  of  a  pair  of  unit  characters,  but  only  one  or 
the  other.  It  thus  follows  that  from  the  standpoint  of  a  single  pair  of 
unit  characters  (e.  g.,  color  of  iris)  there  are  two  categories  of  eggs  and 
likewise  of  sperm.  According  to  the  laws  of  chance  there  will  then  be  one 
chance  for  the  determiner  of  either  character  (e.  g.,  gray  and  white  coat) 
to  meet  its  like,  to  two  chances  that  it  may  meet  its  opposite,  hence  the 
formula  1 :2  :1 : 

The  central  concepts  of  Mendelian  inheritance  thus  are  (1)  unit  char- 
acters; (2)  the  phenomenon  of  dominance;  and  (3)  the  principle  of  seg- 


478  GENERAL  CONSIDERATIONS 

regation,  producing  a  purity  of  the  germ  cells.  The  unit  chaiacters  are 
external  features,  the  hypothecated  determiners  for  these  are  provision- 
ally located  in  the  chromosomes. 

Sex  is  of  course  inherited  in  the  sense  that  an  individual  resembles 
either  its  father  or  its  mother  in  respect  of  sex.  Moreover,  considering  a 
species  as  a  group,  the  two  sexes  are  approximately  numerically  equal. 
This  is  the  ratio  expected  when  a  Mendelian  pure  recessive  (homozygote) 
is  crossed  with  a  hybrid  dominant  (heterozygote) — for  again  by  the  laws  of 
chance,  the  chances  are  equal  that  a  determiner  shall  meet  with  its  oppo- 
site or  its  like.  On  the  basis  of  these  considerations  mainly,  coupled  with 
the  data  of  sex-linked  inheritance  (see  Morgan,  "Heredity  and  Sex."  1915), 
sex  is  conceived  by  some  to  be  inherited  in  Mendelian  fashion,  the  indi- 
vidual with  a  single  accessory  (male)  being  regarded  as  the  heterozygote, 
that  is,  digametic;  that  with  two  accessories,  the  homozygote,  that  is,  the 
homogametic.  However,  such  serious  contradictions  and  difficulties  arise 
when  the  matter  is  thus  strictly  interpreted  that  a  simple  Mendelian  view 
of  sex  ratios  must  probably  be  abandoned.  In  any  event  the  interpretation 
that  regards  the  heterochromosome,  when  present  in  the  duplex  condition, 
as  in  the  female,  as  an  inhibitor  to  male  sex  development  from- the  viewpoint 
of  secondary  sex  characters,  accords  well  with  much  of  the  experimental 
evidence  from  vertebrates.  The  bulk  of  the  best  evidence  tends  to  show 
that  sex  is  determined  at  fertilization,  and  that  it  cannot  thereafter  be 
altered  by  control  of  environmental  conditions.  Relatively  much  chro- 
matin  may  be  thought  to  underlie  the  anabolic  condition  characteristic  of 
femaleness,  relatively  less  chromatin  the  katabolic  conditions  which  sub- 
serve the  high  differentiations  of  maleness. 


Oogenesis. — We  must  now  return  to  a  detailed  description  of  the 
oogenesis.  Splendid  material  for  the  presentation  of  the  facts  con- 
cerning this  process  is  the  egg  of  Ascaris,  or  that  of  certain  molluscs, 
or  the  more  easily  available  egg  of  some  echinoderm,  e.g.,  starfish.  This 
description  will  confine  itself  to  the  starfish  egg.  The  essential  points 
can  be  well  illustrated  with  this  material  (Plate  D,  Figs.  1-16).  In  con- 
trast to  the  spermatozoon,  which  is  relatively  minute,  highly  motile,  and 
with  a  minimum  amount  of 'cytoplasm,  the  egg  on  the  other  hand  grows 
enormously  in  size  (ratio  of  sperm  to  egg  1 :  500,000  ±),  is  non-motile, 
and  has  a  large  amount  of  cytoplasm  heavily  laden  with  yolk  material. 
This  phase  of  the  oogenesis  is  known  as  the  growth  period;  during  the 
early  portions  of  this  period  synapsis  occurs,  and  subsequently  chro- 
matic material  (chromidia)  appears  in  the  cytoplasm,  presumably  ex- 
truded by  the  nucleus,  and  in  part  at  least  changed  into  yolk.  This 
generation  is  the  primary  oocyte,  the  preceding  generation  being 


MALE  ORGANS  OF  REPRODUCTION  479 

odgonial,  primary  and  secondary,  characterized  by  extensive  prolifera- 
tion. The  primary  ob'cyte  divides  in  a  manner  similar  to  the  primary 
spermatocyte,  that  is  by  heterotypic  mitosis,  but  the  daughter-cells  are 
very  unequal  in  size,  each,  however,  with  the  same  number  of  chromo- 
somes (18)  ;  the  small  abortive  cell  is  called  the  polar  body,  or  better 
polocyte,  while  the  large  cell  becomes  a  secondary  oocyte.  Both  polocyte 
and  secondary  oocyte  again  divide,  the  end  result  being  three  similar 
polar  bodies  and  one  large  ob'tid  or  mature  ovum,  now  ready  for  fertili- 
zation. It  must  be  recalled  that  the  maturation  process  is  in  essence  a 
process  of  eliminating  one-half  of  the  original  quota  of  chromosomes, 
and  a  quantitative  reduction  of  its  original  amount  of  chromatin  to 
one-fourth.  At  fertilization,  by  fusion  of  egg  and  sperm,  the  specific 
number  of  chromosomes  is  reestablished — differing  in  many  cases  in 
male  and  female  of  the  same  species — and  the  chromosomes  by  growth 
regain  or  even  exceed  their  original  size.  With  this  brief  consideration 
of  the  function  of  the  germ  glands  in  general,  we  may  proceed  to  a 
description  of  the  structure  of  the  male  organs  of  reproduction  and 
subsequently  of  the  female  organs. 


MALE   ORGANS   OF   REPRODUCTION 

These  organs  include  the  penis  and  the  testes,  together  with  their 
accessory  glands,  and  the  excretory  ducts  which  connect  the  testes  with 
the  urethral  canal.  The  excretory  ducts  include  the  epididymis,  ductus 
(vas)  deferens,  seminal  vesicles,  and  ejaculatory  ducts,  and  with  their 
termination  in  the  urethra  there  are  connected  the  ducts  of  the  prostate 
gland  and  the  bulbo-urethral  glands  (of  Cowper),  whose  secretion  mixes 
with  that  of  the  testes  to  form  the  semen.  The  male  urethra  serves  the 
double  function  of  a  urogenital  canal. 

i 

INTERNAL  GENITAL  ORGANS 

Testis 

The  testis  is  -to  be  regarded  as  a  gland  with  a  double  function ;  it 
produces  cells  (spermatozoa),  hence  a  cytogenic  gland;  and  an  internal 
secretion,  hence,  in  part  an  endocrin  gland.  In  connection  with  the 
testis  must  be  considered  also  its  excretory  duct  system,  and  the  various 
glands  accessory  to  it.  The  relationship  of  these  various  structures 
is  shown  in  diagram,  Fig.  418. 


480 


THE  REPEODUCTIVE  SYSTEM 


Ductus  epi- 
didymidis 


Lobuli  epididymidiS'-t 


Ductuli  efferentes  ----- 
testis 


The  testis  is  encased  in  a  robust  fibro-elastic  capsule,  the  tunica 
albuginea,,  the  innermost  layer  of  which  is  of  looser  texture  and  very 
vascular,  hence  called  the  tunica-  vasculosa.  External  to  the  albugiuea 
is  a  double-layered  sac  of  peritoneum,  the  tunica  vaginalis,  its  visceral 
layer  closely  adherent  to  the  capsule.  The  human  testis  measures 
about  one  and  one-half  inches  in  length,  one  and  one-quarter  inches  in 
width  and  one  inch  in  thickness.  Septa  continuous  with  the  capsule 

divide    it    into    a 
Ductus  deferens        n  u  m  b  e  r  of  com. 

partments  or  lo- 
bules, pyramidal  in 
shape,  the  apices 
converging  to  an 
anterodorsal  mass 
of  dense  connective 
tissue,  the  medias- 
tinum testis  (cor- 
pus Ilighmori), 
corresponding  to  a 
hilum.  The  lobules 
contain  each  sev- 
eral, frequently  two, 
extensively  convo- 
luted tubules,  the 
seminiferous  tu- 
bules (tubuli  con- 
torti).  When  un- 
coiled they  measure 
from  one  to  two 
feet.  The  entire 

testis  contains  several  hundred  lobules;  the  number  has  been  variously 
estimated  at  from  one  hundred  to  four  hundred. 

Bremer  (Amer.  Jour.  Anat.,  11,  4,  1911)  describes  the  tubuli  con- 
torti  of  man  as  tubules  that  may  be  single,  ending  blindly,  may  branch 
or  may  anastomose.  Huber  and  Curtis  (Anat.  Eec.,  .7,  6,  1913),  on 
the  contrary,  state  that  in  the  adult  rabbit  the  seminiferous  tubules 
"present  no  blind  ends,  diverticula  or  nodular  enlargements."  Their 
simplest  form  is  that  of  an  arch  beginning  and  ending  in  a  fubulus 
rectus.  The  two  limbs  may  lie  in  adjacent  lobules.  Complex  tubules 
are  also  described,  resulting  from  the  linkage  of  from  three  to  twelve 


FIG.  425.- 


Corpus  epi- 
didymidis 


Ductulus  aberrans 
(inferior) 

-THE  TESTICLE  WITH  ITS  SYSTEM  OF  EFFEKENT 
PASSAGES. 

Natural  size.     (After  Toldt.) 


MALE  ORGANS  OF  EEPRODUCTION  481 

simple  arched  tubules.  According  to  Curtis  (1915)  branches  and 
anastomoses  of  seminiferous  tubules  are  infrequent  in  the  mouse  testis, 
more  frequent  in  dog.  and  most  frequent  in  rabbit. 

The  testis  is  lodged  in  the  scrotum.     The  wall  of  the  scrotum  is 
essentially  like  the  general  integument,  except  that  it  may  be  more 


Mr    Hi,, 

f?%r*~'.  ..^%-W     f 

,:*I-  ^-Itv 


FIG.  426. — SEMINAL  TUBULE  OF  A  MAN  IN  TRANSECTION. 

a  and  6,  interstitial  cells,  the  latter  containing  coarse  granules;  c,  connective 
tissue  cells;  d,  a  mast-cell  of  the  connective  tissue.  Within  the  tubule  several  phases 
of  spcrmatogenesis  are  well  shown.  Highly  magnified.  (After  Spangaro.) 

highly  pigmented.  Its  subcutaneous  layer,  however,  is  looser  in  texture 
and  contains  more  elastic  tissue  and  smooth  muscle.  It  is  known  as  the 
dart  os. 

The  wall  of  the  seminiferous  tubules  consists  of  fibre-elastic  tissue. 
They  are  lined  with  a  several  layered  epithelium,  the  cells  representing 
the  several  stages  of  spermatogenesis.  In  addition  to  the  germ  or  sex 
cells,  the  epithelium  contains  sustentacular  cells  (Sertoli  cells),  to  which 
the  spermatids  become  attached  during  process  of  metamorphosis  into 
ripe  spermatozoa  (spermia).  It  seems  probable  that  the  spermatids  also 


482 


THE  REPRODUCTIVE  SYSTEM 


draw  nourishment  from  the  sustentacular  cells  for  the  work  of  metamor- 
phosis, hence  also  known  as  'trophocytes.'  The  sustentacular  cell  is 
roughly  of  tall  columnar  shape,  tapering  somewhat  irregularly  toward 
the  distal  pole.  The  proximal  pole  contains  the  nucleus  and  frequently 
flares  somewhat  giving  the  entire  cell  a  tall  pyramidal  shape.  The 
nucleus  is  pale  and  contains  one  or  several  chromatic  nucleoli.  The 
spermatozoa  are  embedded  head  first,  four  to  eight  or  more  to  a  cell, 
in  the  protoplasm  of  the  trophocyte.  Such  a  composite  group  consti- 


FIG.  427. — SEBTOLI  CELLS  OF  THE  HUMAN  TESTIS. 

At  showing  a  crystalloid  (of  Charcot)  and  lipoid  granules  and  spherules;  below 
to  the  right  a  spermatogonium  with  a  crystalloid  (of  Lubarsch).  B  shows  a  crys- 
talloid and  two  accessory  rods,  and  lipoid  granules  and  droplets.  C  shows  at  the 
base  a  crystalloid  and  one  accessory  rod,  and  at  the  summit  two  accessory  rods. 
X  600.  (Winiwarter.) 


tutes  a  so-called  spermatoblast  of  von  Ebner.  The  sustentacular  cell 
contains  one  or  several  crystalloids.  Their  origin  and  function  is  un- 
known. They  were  regarded  by  Montgomery  as  probably  sustentacular 
cell  determinants,  having  been  traced  by  him  from  the  common  mother- 
cells  of  both  trophocyte  and  spermatogonium  into  the  former,  the  latter 
being  said  to  lack  these  elements.  However,  Winiwarter  (Fig.  427)  re- 
ports similar  crystalloids  in  both  trophocytes  and  spermatogonia.  Tro- 
phocytes more  probably  have  an  origin  distinct  from  that  of  the 
germ-cells,  according  to  certain  investigator's  arising  from  the  Bowman's 
capsule  of  the  Wolffian  tubules  of  the  mesonephros. 

Every  section  of  a  tubule  of  an  active  testis  contains  several,  some-- 
times all  the  stages  of  spermatogenesis.  Since  the  spermatogenetic 
process  generally  travels  in  waves,  a  longitudinal  section  is  most  favor- 


7 

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sg  * 

ft! 


484 


THE  REPRODUCTIVE  SYSTEM 


able  for  a  study  of  the  continuous  process.  From  wall  to  lumen  of 
tubules  can  be  seen,  at  successive  levels,  spermatogonia,  primary  spernia- 
tocytes,  secondary  spermatocytes  (prespermatids),  spermatids,  and  sper- 
matozoa attached  to  the  tips  of  the  sustentacular  cells.  Mitoses  can 
frequently  be  seen  in  spermatogonia,  primary  and  secondary  spermato- 


FIG.  429. — SUCCESSIVE  STAGES  IN  THE  METAMORPHOSIS  OF  THE  SPEIMATID  INTO 
THE  SPERMATOZOON. 

(Schematic,  from  Bonnet,  after  Meves.) 

cytes.  The  primary  spermatocytes  are  the  largest  of  the  germ  cells; 
the  secondary  spermatocytes  are  approximately  half  the  size  and  lie 
distal,  while  the  spermatids  are  approximately  one-fourth  the  size;  the 
spermatids  may  be  at  any  stage  of  a  continuous  process  of  metamorpho- 
sis involving  nuclear,  cytoplasmic,  and  general  form  changes.  The 
spermatogonia  are  of  various  sizes,  frequently  approximating  that  of 
the  primary  spermatocytes,  but  always  lie  peripherally,  on  the  basement 
membrane  between  sustentacular  cells.  The  above  named  marks  con- 
stitute the  grosser  criteria  for  identifying  the  several  generations  of 


MALE  ORGANS  OF  REPRODUCTION 


485 


cells  involved   in   spermatogenesis.     As   concerns   details,   the   criteria 
above  given  for  the  grasshopper  testis,  can  be  applied. 

The  Spermatozoon.— Spermiohistogenesis,  however,  differs  some- 
what. The  spermatid  nucleus  becomes  progressively  more  compact, 
chromatic  and  smaller.  At  the  same 
time  it  moves  toward  one  pole  of  the 
cell,  the  cytoplasm  flowing  back- 
ward, except  for  a  thin  envelope 
(irulca  capitis)  which  terminally 
forms  a  covering  for  the  perfora- 
torium  which  represents  a  portion 
(acrosome)  of  the  original  idiosome. 
The  idiosome  is  the  germ-cell  repre- 
sentative of  the  archoplasmic  com- 
plex. Concurrently  with  the  changes 
outlined  for  the  nucleus  it  liberates 
a  centrosome,  and  centrosome  and 
acrosome  pass  to  opposite  poles  of 
the  nucleus.  The  centrosome  di- 
vides into  two  moieties,  a  proximal, 
which  becomes  attached  to  the  nu- 
clear membrane,  and  a  distal,  which 
moves  peripherally  at  the  same  time 
sprouting  a  flagellum,  the  central 
filament.  Meanwhile  a  peripheral 
portion  separates  from  the  more 
central  portion  of  the  distal  centro- 
some and  moves  backward  over  the 
central  filament  enclosing  an  envel- 
oping column  of  cytoplasm,  the  mid- 
dle piece,  in  which  mitochondria 
have  aggregated.  The  mitochondria 
fuse  to  form  a  filament,  the  spiral 
fUtinic.nt,  which  becomes  spirally  ar- 
ranged about  the  central  filament, 
grow  distally  beyond  the  final  locus  of  the  ring  centrosome,  and  together 
with  an  envelope  of  cytoplasm  constitutes  the  tail  of  the  spermatozoon. 
A  short  terminal  naked  portion  of  the  central  filament  is  known  as  the 
terminal  filament. 

Summarizing  the  above:     The   nucleus  becomes  the  head  of  the 


Main    segment  of 
tail 


Oalea  capitis 


--  Spiral  fibers 

...  Sheath  of  axial 
thread 


-  Axial  thread 


Capsule 


Terminal  filament    . 


FIG.  430. — DIAGRAM  OF  HUMAN  SPER- 
MATOZOON. 

(After  Bonnet.) 


The  central  filament  continues  to 


486 


THE  REPEODUCTIVE  SYSTEM 


spermatozoon.     This  is  tipped  with  an  acrosome,  a  derivative  of  the 
idiozome,  and  covered  by  the  galea  capitis,  the  two  comprising  the  per- 
foratorium.      The   other   constituents   of    the    idiozome   contribute   the 
central  filament.     The  extent  between  distal  and 
/IB          C  proximal   centrosomes   constitutes   the   neclc;   the 

portion  between  distal  centrosome  and  ring  cen- 
trosome the  connecting  or  middle  piece  (body), 
with  its  spiral  filament  derived  from  mitochon- 
dria. The  tail  or  flagellum  consists  of  central 
filament  enveloped  by  cytoplasm.  In  many  forms 
a  spiral  fin  develops  on  the  tail.  Also,  there  is 
endless  variation  with  reference  to  the  shape  of 
the  head.  But  the  development  and  morphology 
of  spermatozoa  of  all  vertebrate  forms  is  essen- 
tially the  same.  At  fertilization  only  head  and 
middle  piece — nucleus  and  centrosome  and  mito- 
chondria— enter  into  the  egg,  the  tail  being  gen- 
erally left  behind. 

The  human  spermatozoon  has  a  length  of  from 
fifty  to  sixty  microns.  Of  the  total  the  head  con- 
stitutes about  5  /*,  the  middle  piece  about  5  /*  and 
the  end-piece  about  10  p..  Seen  en  face  the  head 
has  an  avoid  shape ;  in  profile  it  appears  pyrif orm, 
due  to  a  thinning  along  its  terminal  margin.  Oc- 
casionally atypical  or  monstrous,  double-headed, 
multiple-tailed,  and  giant  spermatozoa  appear ;  but 
these  are  probably  non-functional.  Though  flagel- 
late, the  spermatozoa  are  non-motile  until  they 
reach  the  epididymis,  where  they  become  bathed  in 
a  secretion.  Their  motility,  however,  is  not  pro- 
nounced until  they  reach  the  place  in  the  excretory 
passage  where  the  secretion  of  the  seminal  vesicles, 
prostate  and  bulbo-urethral  glands  are  present. 
The  mixture  of  these  secretions  with  the  sperm 
forms  the  semen. 

The  spermatozoa  can  withstand  considerable  variations  in  tempera- 
ture, but  they  are  very  susceptible  to  acid  solutions;  they  survive  best 
in  slightly  alkaline  media.  Under  favorable  conditions  spermatozoa 
may  be  kept  alive  for  as  long  as  eight  days;  it  is  probable  that  they 
remain  alive  for  even  a  longer  time  in  the  female  genital  tract;  but 


FIG.  431.— SPERMATO- 
ZOA OF  VARIOUS  AN- 
IMALS. 

A,  from  the  badger; 
B,  from  the  bat.  Re- 
drawn after  Ballowitz. 
X  1200.  C,  from  the 
rat.  Hematein  and  eo- 
sin.  X  1200. 


MALE  ORGANS  OF  REPRODUCTION 


487 


it  is  uncertain  whether  they  can  maintain  their  functional  virility  for 
this  length  of  time.  The  number  of  spermatozoa  per  cubic  millimeter 
has  been  estimated  at  60,876;  and  the  total  in 
an  average  ejaculation  at  200,000,000  (Lode, 
1896). 

The  tubuli  convoluti  pass  into  short  tubuli 
recti  and  the  latter  into  the  rete  testis  of  the 
mediastinum.  The  rete  testis  is  the  beginning 
of  the  excretory  duct,  and  consist  of  a  meshwork 
of  irregular  tubules  lined  with  a  single  layered 
cuboid  non-ciliated  epithelium.  They  connect 
Avith  a  group  of  greatly  coiled  tubules,  the  duc- 
tuli  efferentes,  from  ten  to  fifteen  in  number, 
each  terminally  winding  so  as  to  assume  a  coni- 
cal shape,  hence  coni  vasculosi — which  tubules 
empty  into  the  distal  portion  of  a  common  duct 
— the  ductus  epididymis.  This  portion  of  the 
duct,  together  with  the  efferent  ductuli,  consti- 
tute the  globus  major  of  the  epididymis.  Con- 
sideration of  the  duct  system  will  follow  below. 
Interstitial  Cells  of  Leydig.— Here  should 
be  considered  the  intertubular  connective  tissue 
of  the  testis.  Fibro-elastic  connective  tissue  acts 
as  a  supporting  stroma  for  the  testicular  paren- 
chyma of  the  seminiferous  tubules.  Scattered 
throughout  this  stroma,  between  the  adjacent 
tubules,  are  peculiar  large  polygonal  cells,  inter- 
stitial cells  of  Leydig,  either  scattered  or  ar- 
ranged in  masses.  The  condition  of  the  nucleus 
varies  from  pale  vesicular  to  dense  deeply  chro- 
matic. Division  figures  are  exceedingly  rare 

among  them,  though  an  occasional  cell  may,  in  young  testes,  be  seen  in 
mitosis.  In  older  testes  an  occasional  nucleus  may  be  seen  in  what 
appears  to  be  amitotic  division.  A  number  of  the  cells  also  are  bi-  and 
multinucleate.  However,  multiplication  of  specific  interstitial  cells  is 
evidently  exceptional.  These  cells  arise  directly  through  modification  in 
shape,  and  growth  from  the  fusiform  and  irregular  connective  tissue 
cells  of  the  stroma.  Moreover,  this  process  seems  to  be  reversible.  They 
thus  represent  a  transient  phase  in  the  life  of  certain  cells  of  the  inter- 
tubular  connective  tissue.  Their  cytoplasm  contains  crystalloids  (mito- 
31 


FIG.  432.  —  SPERMATO- 
ZOA FROM  THE  SEMEN 
OF  MAN. 

A,  usual  type;  B, 
'giant'  double  sperma- 
tozoon. Hematein  and 
eosin.  X  1200. 


488 


THE  KEPRODUCTIVE  SYSTEM 


choudria)  arid  fatty  granules.  The  nature  of  the  lipoid  granules  is  dis- 
cussed by  Whitehead  (Amer.  Jour.  Anat.,  14,  1,  1912).  These  cells 
increase  in  number  during  senile  atrophy  of  the  testis,  but  later  entirely 

disappear.  They  are  rela- 
tively larger  and  more  abun- 
dant also  in  the  testes  of 
tuberculous  patients  where 
there  is  considerable  degen- 
eration and  a  general  in- 
fantile condition  of  the 
seminal  epithelium.  Vari- 
ous functions  have  been 
ascribed  to  them — that  is, 
those  obviously  dependent 
upon  the  internal  secretion 
of  the  testes — prominently, 
origin  and  maintenance  of 
secondary  sexual  characters, 
and  basis  of  sexual  in- 
stinct. Obviously  other  cells 
of  the  testis  might  conceiv- 
ably subserve  these  func- 
tions, namely,  the  susten- 
tacular  cells  and  the  sex- 
cells.  However,  observa- 
tions on  testes  of  mules  (in- 
fertile) and  cryptorchid 
horses,  and  the  findings  of 
Whitehead  (Anat.  Rec.,  2, 
5,  1908)  in  a  third  abdom- 
inal testicle  of  a  horse 
where  only  interstitial  cells 
in  great  abundance  persisted  in  normal  condition,  would  seem  to  rele- 
gate these  functions  to  the  interstitial  cells. 

Kingsbury's  careful  studies  (Amer.  Jour.  Anat.,  16,  1914)  of  the  inter- 
stitial cells  of  the  ovary  of  the  eat  (elements  presumably  homologous  with 
the  interstitial  cells  of  the  testis)  strongly  support  the  interpretation  of 
these  cells  in  terms  of  absorbers  of  degenerating  and  disintegrating  ma- 
terials. In  the  ovary  all  of  the  earliest  and  many  of  the  later  primary 
ob'cytes  disintegrate.  In  the  vicinity  of  such  atretic  follicles  interstitial 


FIG.   433. — A  GROUP  OF  INTERSTITIAL  CELLS 

FROM    THE    TESTIS    OF    A    THIRTY-FIVE    YEAR 

OLD  NEGRO. 

The  outlines  of  three  adjacent  seminiferous 
tubules  are  shown.  Among  the  interstitial  cells 
are  three  nuclei  of  ordinary  connective  tissue. 
The  interstitial  cells  are  filled  with  lipoid  spher- 
ules and  granules.  Formalin  fixation,  iron- 
hematoxylin  stain.  X  1500. 


MALE  OKGANS  OF  REPRODUCTION  489 

cells  laden  with  lipoid  debris  are  abundant.  Their  presence,  however,  is 
transient,  and  their  abundance  reciprocal  to  the  abundance  of  degenerat- 
ing follicles.  This  observation,  reasoning  by  analogy,  would  explain  their 
abundance  in  the  testes  of  cryptorchid  horses,  mules,  and  in  the  third 
abdominal  testicle;  for  here  also  degenerative  processes  are  going  on  among 
the  sex  cells.  Testicles  of  cryptorchid  horses  and  mules  are  characterized 
by  an  unusual  abundance  of  interstitial  cells,  and  degeneration  of  sex  cells. 
These  animals  experience  heat,  but  are  infertile;  this  was  true  also  of  the 
stallion  from  whom  two  testicles  had  been  removed  and  in  whom  subse- 
quently the  third  abdominal  testicle  was  discovered.  These  observations 


ABC  D 

FIG.  434. — INTERSTITIAL  CELLS  FROM  THE  HUMAN  TESTIS. 

A,  B,  and  C,  from  a  twenty-five  year  old  man;  A  shows  the  idiosome,  bacilfery 
centrosomes,  lipoid  granules  and  crystalloids;  B,  with  two  nuclei;  C,  with  four 
nuclei  (probably  the  result  of  amitotic  division)  and  eight  centrosomes.  D,  from 
a  41-year-old  man,  showing  large  and  small  crystalloids.  Highly  magnified.  (Wini- 
warter,  Anat.  Anz.,  41,  11,  1912.) 

would  seem  to  indicate  that  the  sexual  instinct  depends  upon  an  internal 
secretion  on  the  part  of  the  interstitial  cells.  The  two  results  can  be  har- 
monized on  this  basis:  The  internal  secretion  may  actually  be  formed  by 
the  cells  of  the  seminiferous  tubules;  when  these  degenerate  the  products 
are  removed  by  the  interstitial  cells;  since  even  in  healthy  testes  there  is 
some  degeneration  of  sex  cells,  all  testes  contain  a  few  interstitial  cells; 
these  are  more  abundant  at  puberty ;  the  secretory  products  of  degenerating 
sex  cells  are  included  among  the  debris  removed  by  the  interstitial  cells 
from  which  they  may  be  passed  into  the  capillaries  of  the  testicular  stroma. 
The  suggestion  that  the  interstitial  cells  are  in  some  way  connected 
with  secondary  sex  characters  seems  disproved  by  various  castration  experi- 
ments. For  example,  the  spayed  hen  takes  on  male  secondary  sexual  charac- 
ters; if  these  were  dependent  exclusively  upon  the  interstitial  cells  of  the 
testis,  they  could  not  appear  in  the  absence  of  both  ovaries  and  testes. 


490  THE  KEPEODUCTIVE  SYSTEM 

However,  the  experiments  of  Steinaeh  (Zentralblatt  f.  Physiol.,  27,  14, 
1913)  cannot  be  ignored  in  this  connection.  Steinaeh  made  reciprocal 
transplantations  of  testes  and  ovaries  in  young  male  and  female  rats  and 
in  guinea  pigs,  and  claims  to  have  succeeded  in  changing  a  potential 
female,  from  the  view  point  of  secondary  sex  characters  (both  physical  and 
temperamental),  into  a  male,  and  vice  versa.  A  male  is  said  to  have  devel- 
oped functional  mammary  glands,  and  even  to  have  suckled  young.  Stein- 
aeh interprets  his  results  to  mean  that  not  only  do  the  secondary  sex  char- 
acters of  the  male  and  female  depend  upon  the  presence  of  the  'pubcrtal 
gland'  (interstitial  cells),  but  also  the  fact  whether  the  undifferentiated 
gonad  shall  develop  into  a  testis  or  an  ovary.  Microscopic  examination  of 
the  transplant  showed  that  everything  suffered  degeneration  except  the  in- 
terstitial tissue,  which  underwent  extensive  hyperplasia.  For  further  in- 
formation on  this  and  related  subjects  reference  should  be  made  to  Mar- 
shall's "The  Physiology  of  Eeproduction,"  1910. 


The  Duct  System 

Tubuli  Recti.—  At  the  apex  of  the  testicular  lobule  the  tortuous 
seminiferous  tubules  pass  into  the  rete  testis  of  the  mediastinum.  At 
this  point  the  tubule  becomes  straight  and  is  abruptly  narrowed.  Thus 
the  short  straight  tubules,  tubuli  recti,  are  formed.  In  the  straight 
tubules  the  stratified  epithelium  of  the  tortuous  portions  is  abruptly 
exchanged  for  a  very  low  columnar  or  flattened  type  of  epithelium  with 
which  the  Sertoli  cells  of  the  tortuous  tubules  seem  to  be  continuous. 
The  straight  tubules  are  very  short  and  are  soon  transformed  into  the 
irregular  anastomosing  canals  of  the  rete  testis. 

Rete  Testis. — The  connective  tissue  of  the  mediastinum  is  perme- 
ated by  a  network  of  irregular  channels  of  varying  diameter  which 
present  frequent  dilatations  and  often  have  the  appearance  of  broad 
cleft-like  spaces.  These  are  the  canals  of  the  rete  testis  which  form  a 
dense  network  of  anastomosing  channels.  On  the  one  hand  they  receive 
the  straight  tubules,  and  on  the  other  they  pass  into  the  ductuli  ef- 
ferentes,  which  convey  the  secretion  onward  to  the  globus  major  of  the 
epididymis. 

The  canals  of  the  rete  testis  are  lined  by  cuboidal  or  flattened  epi- 
thelium, which  rests  upon  a  delicate  basement  membrane.  This  in 
turn  is  supported  by  the  connective  tissue  of  thej  mediastinum.  The 
broad  but  irregular  lumen  of  the  canals  is  occupied  by  the  secretion 
from  the  seminiferous  tubules  and  contains  many  spermatozoa. 

Ductuli  Efferentes, — As  the  tubules  of  the  rete  testis  leave  the 


MALE  ORGANS  OF  REPEODUCTION 


491 


mediastinum  they  are  abruptly  transformed  into  peculiar  efferent  ducts, 

10  to  15  in  number,  which  pass  into  the  glolms  major  of  the  epididymis 

and  by  means  of  spiral  windings  form  conical  masses,  coni  vasculo&i, 

whose  apex  projects  into  the  glo- 

bus   major.      The   epithelium   of 

these  tubules  is  peculiar  in  that 

it  contains  two  varieties  of  cells, 

and    in   that   it    is    thrown    into 

many      prominent      longitudinal 

folds   or  ruga?. 

In  the  lining  epithelium  there 
are  short  columnar  cells  which  FIG.  435.— A  SMALL  PORTION  OF  THE  WALL 
rest  upon  the  basement  mem-  °F  AN  EFFERENT  DUCTULE  OF  THE  TES- 
brane  and  carry  upon  their  free 

ends  a  tuft  of  short  cilia.    These      d>  '?lands' in  longitudinal  section;  d',  the 
,,    ,  ...          .  same  in  oblique  section;  F,  ciliated  epithe- 

cells  have  an  ovoid  nucleus  and  a  iium.    x  140.    (After  K611iker.) 

very   finely   granular,    eosinoph-il 

cytoplasm.     Between  and  among  the  ciliated  cells  are  many  broad  col- 
umnar or  polyhedral  cells,  having  remarkably  clear  cytoplasm,  which 


FIG.  436. — EFFERENT  DUCTULES  OF  THE  RABBIT'S  EPIDIDTMIS. 
Hematoin  and  oosin.     Photo.     X  250. 


492  THE  REPRODUCTIVE  SYSTEM 

chiefly  occur  between  and  at  the  base  of  the  rugae,  and  are  frequently 
arranged  in  small  groups  simulating  minute  secreting  glands.  These 
clear  cells  have  spheroidal  nuclei  and  their  cytoplasm  is  filled  with  large 
coarse  granules.  They  are  quite  characteristic  of  this  portion  of  the 
excretory  tubules  of  the  testis.  The  coni  vasculosi  form  a  considerable 


FIG.  437. — SEVERAL  COILS  OF  THE  RABBIT'S  EPIDIDYMIS  IN  TRANSECTION. 
The  lumen  of  the  tubules  contains  groups  of  spermatozoa.    Hematein  and  eosin. 
Photo.     X  178. 

portion  of  the  globus  major  of  the  epididymis.  The  epithelium  rests 
upon  a  well-developed  basement  membrane,  outside  of  which  is  a  robust 
layer  of  circularly  disposed,  smooth  muscle  cells  with  intermingled 
elastic  fibers.  The  nuclei  of  the  lining  cells  can  frequently  be  seen  in 
some  stage  of  amitotic  division. 

Epididymis. — The  ductus  epididymis  forms  a  long-  coiled  tubule 
whose  convolutions,  by  their  regular  cylindrical  form  and  their  tall 
ciliated  epithelium,  are  sharply  distinguished  from  those  of  the  ductuli 


MALE  ORGANS  OF  REPRODUCTION  493 

efferentes,  which  have  much  thinner  walls.  The  lining  epithelium  of 
the  epididymis  is  of  the  tall,  ciliated,  simple  columnar  type  with  elon- 
gated ovoid  nuclei,  a  finely  granular  cytoplasm,  and  a  group  of  non- 
motile  cilia  which  often  adhere  together  to  form  a  peculiar  tuft  or 
cluster  ('brush  border').  At  the  base  of  the  ciliated  cells  is  an  in- 
complete layer  of  basal  epithelium,  whose  flattened  cuboidal  elements 
are  wedged  between  the  bases  of  the  tall  columnar  cells.  The  two- 
layered  epithelium  is  thus  of  the  pseudo-stratified  type.  The  cells  ap- 
parently multiply  largely  by  amitosis. 

The  epithelium  rests  upon  a  cellular  basement  membrane,  which  is 
supported  by  a  connective  tissue  tunic  of  varying  thickness.  In  addi- 
tion to  many  elastic  fibers,  this  coat  contains  a  few  smooth  muscle 
cells.  The  coils  of  the  epididymis  are  firmly  united  into  a  solid  mass 
by  means  of  the  dense  intervening  connective  tissue.  They  form  the 
whole  of  the  globus  minor  and  a  considerable  portion  of  the  globus 
major.  When  unraveled  the  duct  of  the  epididymis  measures  about 
twenty  feet  in  length. 

The  Ductus  Deferens  ( Vas  Deferens) . — This  duct  is  a  continua- 
tion of  the  epididymis,  whose  course  now  becomes  relatively  straight. 
It  measures  about  eighteen  inches  in  length.  In  this  portion  of  the 
excretory  duct  of  the  testis  the  lining  epithelium  soon  loses  its  cilia, 
and  the  basal  cells  become  more  prominent.  Hence  in  the  greater 
portion  of  its  course  the  ductus  deferens  is  lined  by  tall,  columnar, 
non-ciliated  epithelium,  with  low  basal  cells  between  the  attached  ends 
of  the  columnar  cells. 

The  epithelium  rests  upon  a  fibro-cellular  basement  membrane, 
which  is  supported  by  a  fibrous  tunica  propria.  This,  in  turn,  passes 
almost  insensibly  into  the  muscular  coat  which  consists  of  two  layers, 
an  inner  circular  and  an  outer  longitudinal,  both  of  which  are  highly- 
developed.  In  the  lower  portions  of  the  ductus  deferens,  a  thin  internal 
layer  of  longitudinal  muscle  fibers  is  also  found.  The  fibers  of  the 
internal  and  middle  circular  layers  are  frequently  less  regularly  ar- 
ranged, in  which  case  their  oblique  bundles  interlace  with  one  another 
in  a  most  intricate  manner.  The  very  thick,  smooth  muscular  coat 
and  the  relatively  narrow  lumen  give  this  portion  of  the  duct  a  firm 
consistence  and  a  cord-like  feel. 

In  its  ampulla — the  dilated  portion  near  its  prostatic  termination — 
the  mucous  membrane  of  the  ductus  deferens  is  more  loosely  attached 
and  the  folds  or  rugae,  which  elsewhere  are  few  in  number,  are  here 
very  pronounced.  The  lumen  of  the  ampulla  is  broad,  but  elsewhere 


494  THE  REPRODUCTIVE  SYSTEM      , 

the  lumen  of  the  duct  is  narrow,  as  compared  with  its  exceptionally 
thick  muscular  wall.  As  elsewhere  in  the  excretory  canal  of  the  testicle, 
the  lumen  of  the  ductus  deferens  contains  many  spermatozoa. 

THE  SPERMATIC  CORD. — The  spermatic  cord  in  its  scrotal  portion. 


FIG.  438. — TRANSECTION  OF  THE  DUCTUS  DEFEKENS  OF  A  DOG. 
Hematein  and  eosin.     Photo.     X  104. 

in  addition  to  the  ductus  deferens,  contains  a  mass  of  connective  tissue 
in  which  are  embedded  the  smooth  muscle  fibers  of  the  internal  cre- 
master  muscle,  the  spermatic  artery,  veins,  and  nerve  plexus,  and  the 
vessels  of  the  pampiniform  plexus.  Closely  associated  with  these  con- 
stituents is  also  the  striated  cremaster  muscle  proper.  The  whole  is 
invested  by  a  reflection  of  the  tunica  vaginalis. 

The  pampiniform  plexus  is  a  considerable  group  of  venous  spaces, 
usually  completely   collapsed   after   death,  which   are   characterized   by 


MALE  ORGANS  OF  REPRODUCTION 


495 


very  thick,  firm,  fibronmscular  walls.  The  vessels  are  embedded  in 
dense  connective  tissue,  and  the  whole  plexus  in  general  appearance 
somewhat  resembles  the  erectile  tissues. 


FIG.  439. — FROM  A  SECTION  THROUGH  THE  WALL  OF  A  SEMINAL  VESICLE  OP  MAN. 
a,  mucosa;  b,  muscular  coat;  c,  fibrous  coat.    Hematein  and  eosin.    Photo.    X  185. 

The  Seminal  Vesicles. — The  walls  of  the  seminal  vesicles  consist 
of  a  thin  outermost  coat  of  connective  tissue  in  which  are  many  small 
ganglia,  a  muscular  coat  similar  to  that  of  the  ductus  deferens  but 


496 


THE  REPRODUCTIVE  SYSTEM 


much  thinner,  and  a  characteristic  nmcosa.  The  tunica  propria  of  the 
mucous  membrane  is  a  thin  layer  of  delicate  cellular  connective  tissue 
which  loosely  attaches  the  lining  epithelium 
to  the  muscular  coat.  The  surface  of  the 
mucosa  presents  numerous  folds  which  not 
only  form  longitudinal  rugge  but  also  pos- 
sess an  intricate  network  of  secondary  ridges 
which  are  both  longitudinal  and  transverse 
in  direction.  This  peculiar  arrangement  re- 
sults in  the  appearance  of  diverticula  of 
various  forms  and  sizes  which,  except  that 
their  epithelium  does  not  differ  from  that 
of  the  surface,  might  often  be  interpreted, 
when  seen  in  section,  as  representing  sec- 
ondary secreting  glands  within  the  mucosa. 
Slender  processes  of  the  corium  extend  into 
all  the  folds  of  the  mucous  membrane. 

The  lining  epithelium  of  the  seminal 
vesicles  is  of  the  columnar  type  and  usually 
contains  but  a  single  layer  of  cells.  Occa- 
sionally basal  cells  are  also  found  in  the 
deeper  part  of  the  epithelial  layer;  in  such 
case  the  epithelium  may  be  said  to  be  of  the 
pseudo-stratified  type.  This  variation  may 
possibly  be  partly  dependent  upon  the  dis- 
tention  or  relaxation  of  the  vesicles.  The 
cells  of  the  epithelium  contain  peculiar 
granules  of  yellowish  pigment  which  are 
present  in  considerable  numbers  and  are 
quite  characteristic  of  the  organ.  The  su- 
perficial cells  appear  to  be  readily  desquam- 
ated, and  together  with  coarse  granules  of 
secretion  form  the  chief  contents  of  the 
lumen.  Occasional  small  concretions  of  ir- 
regular form,  and  homogeneous  or  lamellar 
structure,  similar  to  those  of  the  prostate 
gland,  are  also  found.  The  seminal  vesicles 
usually  contain  but  few  spermatozoa.  Occasionally  these  are  present  in 
large  numbers;  at  other  times  they  may  be  entirely  absent.  Their  chief 
function  is  now  thought  to  be  secretory. 


FIG.  440. — MODEL  OF  A 
RECONSTRUCTED  PROS- 
TATE GLAND  OF  MAN. 

The  figure  includes  one 
lobule.  The  narrow  duct 
expands  and  terminates  in 
a  large  number  of  alveoli  of 
very  varied  size  and  form. 
X  40.  (After  Maziarski.) 


MALE  ORGANS  OF  REPRODUCTION  497 

The  Ejaculatory  Ducts.— These  ducts  are  formed  by  the  union  of 
the  ampulla  of  a  ductus  deferens  and  the  duct  of  a  seminal  vesicle  and 
are  similar  in  structure  to  the  ampullae  of  which  they  are  the  continua- 
tion. The  ejaculatory  ducts,  however,  possess  a  thinner  wall  and  their 
mucosa  presents  the  same  folded  condition  as  in  the  seminal  vesicles, 
but  to  a  lesser  degree.  In  its  prostatic  portion  the  musculature  of  the 
ductus  deferens  blends  with  the  muscular  stroma  of  the  prostate,  so 
that  in  the  ejaculatory  duct  the  smooth  muscle  no  longer  forms  a 
distinctly  lamellated  coat.  On  approaching  the  urethra,  the  epithelium 
of  the  ejaculatory  ducts  presents  a  gradual  transition  to  the  stratified 
epithelium  of  the  urethral  canal. 

Associated  Glands 

The  Prostate  Gland. — This  is  a  compound  tubulo-alveolar  gland 
consisting  of  from  30  to  50  lobules  investing  the  urethra  and  the  ejacula- 
tory ducts.  It  pours  its  serous  secretion,  which  has  a  characteristic 
odor,  into  the  neighboring  portion  of  the  urethra  by  means  of  two  large 
and  many  (15  to  30)  small  ducts.  These  open  either  directly  into 
the  urethral  canal  or  indirectly  through  the  utriculus  prostaticus  (sinus 
pocularis).  The  secreting  alveoli  are  embedded  in  a  very  dense  fibro- 
muscular  stroma  which,  at  the  surface  of  the  organ,  forms  an  unusually 
thick  capsule  in  which  interlacing  bundles  of  smooth  muscle  are  most 
prominent.  This  portion  of  the  stroma  also  contains  intrinsic  striated 
muscle  fibers  in  limited  numbers.  Broad  bands  of  fibromuscular  tissue 
pass  inward  from  the  capsule  and  form  a  network  of  thick  septa  in  the 
meshes  of  which  are  the  glandular  alveoli.  These  septa  converge  toward 
the  urethra,  which  penetrates  the  ventral  portion  of  the  organ,  their 
muscular  fibers  finally  blending  with  the  sphincter  fibers  of  the  prostatic 
portion  of  this  canal. 

The  stroma  consists  of  smooth  muscle  and  connective  tissue;  their 
fibers  are  intimately  blended.  The  muscle  and  connective  tissue  con- 
stitute each  about  one-fourth  of  the  organ.  The  muscle  cells  form 
either  groups  or  bundles  of  variable  size,  or  are  frequently  isolated 
within  the  meshes  of  the  connective  tissue.  Their  extreme  abundance 
— in  some  parts  exceeding  the  connective  tissue  in  volume — is  char- 
acteristic of  the  prostatic  stroma.  The  connective  tissue,  which  is 
sparingly  supplied  with  elastic  fibers,  is  rich  in  cells.  Near  the  se- 
creting alveoli  the  muscle  fibers  are  absent  and  the  cellular  connective 
tissue  becomes  more  prominent. 

The  lining  cells  are  of  the  tall  columnar  type,  sometimes  forming 


498  THE  REPRODUCTIVE  SYSTEM 

a  single,  sometimes  a  multiple  cell  layer.  They  possess  spherical  or 
ovoid  nuclei  which  lie  in  their  deepest  third.  Their  cytoplasm  is  finely 
granular  and  often  contains  small  yellowish  granules.  The  epithelium 
rests  upon  a  prominent  membrana  propria,  composed  of  peculiar  coarse 
collagenous  fibers,  'B-collagenous'  fibers  (Ferguson,  Anat.  Rec.,  5,  12, 
1911)  somewhat  resembling,  but  not  identical  with,  reticulum.  This 


FIG.  441. — SEVERAL  ALVEOLI  OF  THE  HUMAN  PROSTATE  GLAND,  SEEN  IN  SECTION. 
Hematein  and  eosin.    Photo.     X  160. 

type  of  fiber  is  present  also  throughout  the  stroma  and  distinguish- 
able by  the  Bielschowsky  technic  from  the  usual  collagenous  ('A-col- 
lagenous')  fibers. 

The  epithelium  is  remarkably  folded  upon  itself,  the  narrow  interval 
between  the  two  layers  of  the  epithelial  folds  being  always  occupied  by 
delicate  extensions  of  the  connective  tissue  stroma.  The  prominence 
of  the  folds  varies  greatly  in  different  tubules,  some  showing  scarcely 


MALE  OKGANS  OF  REPRODUCTION 


499 


any  such,  the  lumen  of  others  being  subdivided  by  deep  rugae  into 
numerous  anastomosing  compartments.  The  amount  of  the  folding  also 
varies  in  different  species,  being  more  highly  developed  in  some  of 
the  lower  mammals,  e.g.,  the  dog,  than  in  man. 

The  lumen  of  the  prostatic  tubules  is  broad,  and  is  beset  with  numer- 
ous alveolar  dilatations  and  shallow  diverticula.     It  is  usually  broader 


FIG.  442. — PORTION  OF  PROSTATE  GLAND  OF  AN  OLD  MAN,  SHOWING  THE  PROSTATIC 
CONCRETIONS.  • 

In  the  upper  right  hand  concretion  the  concentric  lamellae  are  clearly  discernible. 

near  the  blind  extremity  and  diminishes  somewhat  in  diameter  toward 
the  duct.  The  caliber  of  the  lumen  also  varies  greatly  in  different 
tubules  and  is  possibly  dependent  in  part  upon  the  state  of  secretory 
activity.  The  contents  of  the  lumen  include  the  granular  albuminous 
secretion,  desquamated  epithelial  cells,  and,  as  age  advances,  many  so- 
called  prostatic  concretions  ('corpora  amylacea';  'prostatic  calculi'). 
The  concretions  vary  greatly  in  size  (10  /*.  to  1  mm.  in  diameter), 
and  may  be  homogeneous,  but  more  frequently  present  a  distinctly 


500  THE  REPRODUCTIVE  SYSTEM 

lamellated  appearance.  Prostatic  concretions  may  occur  at  all  ages  but 
increase  both  in  number  and  size  in  later  life.  Occasionally  they  attain 
a  large  size  and  may  become  encysted. 

The  prostatic  ducts  are  lined  by  either  a  single  or  a  pseudo-stratified 
layer  of  columnar  epithelium,  and,  except  for  their  narrower  caliber 
and  more  regular  contour,  they  closely  resemble  the  secreting  tubules. 
As  the  ducts  approach  their  termination  their  epithelium  increases 
the  number  of  its  cell  layers.  The  larger  ducts,  just  prior  to  their 


U  u 

FIG.  443. — PROSTATIC  GENITAL  CORPUSCLES. 

a,  axial  nerve  fiber;  b,  peri-axial  nerve  fiber.     Methylene  blue.     Moderately 
magnified.     (After  Timofejew.) 

termination,  are  lined  by  transitional  epithelium  similar  to  that  of  the 
urethra,  into  which  they  open.  * 

BLOOD  AND  LYMPH  SUPPLY. — The  prostate  gland  possesses  a  rich 
blood  supply.  Its  larger  vessels  are  found  in  the  capsule,  whence 
they  send  branches  into  all  portions  of  the  fibromuscular  stroma,  and 
form  a  rich  capillary  plexus  in  the  connective  tissue  layer  about  the 
epithelium  of  the  secreting  alveoli,  and  a  second  plexus  in  the  substance 
of  the  stroma  itself.  The  prostate  is  abundantly  supplied,  also,  with 
lymphatic  vessels,  which  are  connected  with  the  deep  pelvic  lymph 
nodes. 

The  capsule  of  the  prostate,  as  also  the  neighboring  connective  tissue, 
both  in  relation  with  this  organ  and  with  the  adjacent  seminal  vesicles, 
contains  many  nerve  trunks,  chiefly  sympathetic,  and  small  ganglia. 
The  latter  are  especially  numerous.  In  this  region  a  peculiar  variety 
of  special  nerve  ending  is  found,  It  was  formerly  regarded  as  a  Pa- 


MALI:  <>I;<;ANS  OF  REPRODUCTION 


501 


cinian  corpuscle,  but  differs  somewhat  from  these  bodies.  It  perhaps 
more  nearly  resembles  the  genital  corpuscles.  These  bodies  are  dis- 
tinctly lamcllated  and  possess  a  broad  axial  nerve  fiber  which  some- 
what resembles  that  of  the  end  bulbs  of  Krause.  This  nerve  fiber  is, 


FIG.  445. — FROM  A  SECTION  OF  THE  BUL- 
BO-URETHRAL  (CoWPER's)  GLAND  OF  MAN. 

o,  duct;  6,  tubules;  c,  stroma.     X  130. 
(After  Braus.) 


however,  accompanied  by  another  and  finer  fiber 
which,    as    Timofejew    (Anat.    Anz.,    1896)    has 
shown,  breaks  into  a  close  network  of  fine  fibrils 
STRUCTION  OF  A  BuL-     surrounding  the  axial  nerve  fiber  in  a  peculiar 

BO-URETHRAL  (Cow-        ,        n      ,    ,  ., 

PEB'S)     GLAND    OP     Basket-like  manner. 

The  Bulbo-urethral  Glands  (Cowper's 
Glands). — These  are  two  small  tubulo-acinar  mu- 
surrounded  cus-sccreting  glands  which  are  divisible  into 
numerous  small  lobules.  The  lobules  are  sep- 
a rated  by  connective  tissue  septa  containing  both 
smooth  and  striated  muscle  fibers.  .  The  latter 

are  continuous  with  the  adjacent  compressor  urethra?  muscle.  The  se- 
creting acini  are  lined  by  columnar  cells,  some  of  which  are  finely 
granular  and  stain  with  eosin  and  acid  dyes,  while  others  are  apparently 
filled  with  mucous  secretion  and  react  to  the  specific  dyes  for  mucin. 
Certain  other  tubular  alveoli  are  lined  by  low  cuboidal  or  flattened  epi- 
thelium. The  epithelium  rests  upon  a  distinct  <-<-llular  basement  mem- 
brane. 


FIG.      444.  —  RECON- 


MAN. 

The  tubular  ducts 
are  closel. 
by  the  expanded  alve- 
oli. X  100  (After 
Maziarski.) 


502  THE  EEPEODUCTIVE  SYSTEM 

"  The  interlobular  and  the  smaller  intralobular  ducts  are  also  lined 
by  a  single  layer  of  columnar  cells.  Their  wall  is  supplied  with  smooth 
muscle,  most  of  whose  fibers  have  a  longitudinal  direction.  The  two 
ducts  of  Cowper's  glands  open  into  the  bulbous  portion  of  the  urethra. 

Associated  Vestigial  Structures 

The  vestigial  structures  associated  with  the  male  reproductive  system 
include  the  appendices  testis  and  epididymis,  the  superior  and  inferior  duc- 
tuli  aberrantes,  the  paradidymis  and  the  sinus  pocularis.  Of  these  it  may 
be  said  in  general  that  they  are  more  or  less  variable  with  respect  of  gross 
and  microscopic  structure  and  even  with  respect  of  presence;  that  they 
resemble  histologically  the  structures  with  which  they  are  homologous,  and 
that  they  tend  to  become  cystic. 

The  APPENDIX  TESTIS  is  the  least  variable  of  the  vestigial  associates.  It 
is  present  in  about  ninety  per  cent,  of  cases.  It  is  a  small  spherical,  fre- 
quently pedunculated,  sac  attached  to  the  superior  pole  of  the  testis;  it  is 
covered  with  tunica  vaginalis  and  lined  with  simple  columnar  epithelium, 
sometimes  ciliated,  and  represents  the  end  of  the  degenerated  fetal  Miil- 
lerian  duct. 

The  APPENDIX  EPIDIDYMIS  is  a  very  similar  pedunculated  structure,  much 
less  frequently  present.  It  is  situated  on  the  globus  major  of  the  epididy- 
mis.  It  is  supposed  to  represent  a  degenerated  Wolffian  tubule.  By  some 
it  is  regarded  as  the  atrophic  end  of  the  Wolffian  duct. 

The  DUCTTJLI  ABERRANTES  are  blind  tubules,  the  remnants  of  meso- 
nephric  tubules  which  failed  of  inclusion  among  the  ductuli  efferentes  of 
the  globus  major.  The  superior  ductule  opens  into  the  epididymis  below 
the  globus  major;  the  inferior  opens  at  the  globus  minor;  both  lie  between 
the  testis  and  the  epididymis.  They  are  lined  with  a  single  layer  of  colum- 
nar epithelium,  sometimes  ciliated.  The  inferior  ductule  is  the  more  gen- 
erally present,  and  has  a  length  of  about  five  centimeters. 

The  PARADIDYMIS  (organ  of  Giraldes)  lies  within  the  spermatic  cord 
between  the  head  of  the  epididymis  and  the  pampiniform  plexus.  It  con- 
sists of  a  variable  number  of  irregular  branching  tubules,  blind  at  both 
ends,  and  lined  with  a  single  layer  of  columnar,  ciliated  epithelium.  These 
tubules  also  represent  persisting  rudimentary  mesonephric  tubules. 

The  SINUS  POCULARIS  (sinus  prostaticus)  represents  the  remnant  of  the 
proximally  fused  degenerated  fetal  Miillerian  ducts.  It  is  the  homologue  of 
the  vagina  in  the  female.  It  is  a  shallow,  blind  pocket  opening  into  the 
floor  of  the  prostatic  portion  of  the  urethra ;  it  may  be  bifid  distally,  varies 
in  length  from  six  to  twelve  millimeters,  and  is  lined  with  a  columnar 
epithelium  which  may  be  locally  ciliated, 


MALE    ORGANS    OF    REPRODUCTION 

EXTERNAL  GENITAL  ORGAN 


503 


The  Penis. — The  penis  consists  of  three  masses  of  erectile  tissue, 
the  two  corpora  cavernosa  penis  and  the  corpus  spongiosum  or  corpus 
cavernosum  urethrce,  which  are  firmly  united  by  dense  fibrous  and  areolar 


FIG.  446. — TRANSECTION  OF  A  CHILD'S  PENIS,  JUST  BACK  OF  THE  GLANS. 

The  two  corpora  cavernosa  (fused  in  the  median  line)  and  the  corpus  spongiosum, 
the  latter  containing  the  urethra,  are  well  shown.  The  cutaneous  surface  is  not 
included.  Hematein  and  eosin.  Photo.  X  8. 

connective  tissue.  The  outer  cutaneous  surface  is  loosely  attached  over 
the  body  of  the  organ;  its  structure  does  not  differ  materially  from 
that  of  the  skin  of  other  parts.  The  subcutaneous  tissue  is  remarkable 
for  the  extreme  looseness  of  its  areolae  and  the  absence  of  fat.  In  the 
glans  penis  the  epithelial  covering,  which  is  continuous  with  the  pre- 
pucial  epidermis,  is  firmly  united  to  the  underlying  erectile  tissue. 


504 


THE  KEPEODUCTIVE  SYSTEM 


Each  corpus  cavernosum  is  invested  with  a  thick  sheath  of  very  dense 
fibre-elastic  tissue,  the  tunica  albuginea,  divisible  into  an  inner  circular 
and  an  outer  longitudinal  layer  of  fibers,  and  imperfect  between  the  two 
corpora  cavernosa  penis  where  it  forms  the  pectiniform  septum.  From 
the  inner  surface  of  this  fibrous  coat  connective  tissue  septa,  the  trabec- 
ulas,  pass  in  all  directions  and  form  a  reticular  framework  whose 

fibrous  bands  contain  many  smooth 
muscle  fibers.  In  the  meshes  of  this 
framework  are  characteristic  broad 
venous  sinuses  which  possess  no  true 
wall  other  than  their  endothelial 
lining.  In  the  flaccid  condition  of 
the  organ  the  blood  sinuses  are  com- 
pletely collapsed,  their  walls  are  in 
contact,  and  their  lumina  almost 
obliterated,  which  gives  them  the 
appearance  of  mere  slits  in  the 
dense  connective  tissue  of  the  caver- 
nous body.  When  distended  by  in- 
jection, or,  in  the  erectile  condition 
of  the  organ,  by  blood,  these  spaces 
become  widely  dilated  and  form  true 
blood  sinuses  of  broad  caliber. 

The  blood  supply  of  the  erectile 
tissue  is  peculiar.  The  arteries  ter- 
minate either  (1)  in  capillaries,  (2) 
by  direct  anastomosis  with  the  ven- 
ules,  or  (3)  by  opening  directly  into 


FIG.  447. — HELICINE  ARTERY  IN  SEC- 
TION, FROM  THE  URETHRAL  BULB  OF 
MAN. 


a,  lumen  of  a  helicine  artery;  b, 
fibrous  bands  of  the  erectile  tissue;  c,  c, 
lumen  of  a  venous  blood  space;  m,  open- 
ing of  the  helicine  artery  into  the  blood 
space;  ms,  muscular  coat  of  the  artery. 
Hematoxylin  and  eosin.  X  180.  (Af- 
ter Kolliker.) 

the  venous   sinuses,   in   which   case 

the  minute  terminal  arterioles  have  a  peculiar  looped  appearance 
and  were  described  by  J.  Miiller  (1835)  as  helicine  arteries.  The 
capillaries  form  a  superficial  plexus  beneath  the  tunica  albuginea.  which 
opens  into  a  deeper  plexus  of  broader  vessels  from  which  the  venules 
take  origin.  Blood  following  this  course  through  the  capillaries  and 
into  the  venules  may  not  enter  the  venous  sinuses — a  direction  which 
is  assumed  by  the  greater  portion  of  the  blood  in  the  flaccid  condition 
of  the  organ.  The  deeper  venous  plexus  communicates  freely  with 
the  venous  sinuses  so  that  the  least  obstruction  to  the  usual  venous 
outflow  diverts  the  circulation  through  these  channels. 

The  helicirie  arteries  are  confined  to  the  corpora  cavern osa  penis, 


MALE  ORGANS  OF  REPRODUCTION 


505 


where  they  are  most  abundant  near  the  root  of  the  organ.  The  ar- 
terioles  from  which  they  are  derived  end  by  arborization  in  the  con- 
nective tissue  framework,  their  terminal  twigs  entering  fibrous  processes 
which  project  into  the  venous  sinuses  and  are  frequently  bound  down 
by  delicate  fibrous  bands  which  unite  their  extremity  to  the  wall  of  the 
sinus  and  produce  the  characteristic  looped  condition  when  the  villus- 
like  projection  is  distended  by  the  injection  of  its  arteriole.  When 
partially  injected  the  helicine  arteries  appear  to  end  blindly,  but  when 


•  f.a. 


FIG.  448. — THE  ERECTILE  TISSUE  OF  THE  PENIS. 

c  r,  peripheral  capillary  plexus;  t  o,  tunica  albuginea;  v  s,  venous  spaces;  z,  bands 
of  smooth  muscle  and  vascular  connective  tissue.     X  30.     (After  Kolliker.) 

completely  distended  they  pour  their  contents  -into  the  venous  sinuses. 
The  venous  spaces  at  the  periphery  of  the  erectile  body  are  relatively 
narrow  and  the  intervening  trabeculae  are  thick;  toward  the  axis  of  the 
body  the  sinuses  become  broader  and  occupy  a  relatively  greater  portion 
of  the  tissue.  Here,  also,  their  long  axis,  except  in  the  corpus  spongi- 
osum,  frequently  lies  in  the  transverse  axis  of  the  penis.  Both  the 
arteries  and  the  veins  of  the  erectile  tissue  possess  very  thick  muscular 
walls,  and  in  both,  the  intima  becomes  locally  thickened  by  accumula- 
tions of  longitudinal  muscles  and  elastic  tissue  bulging  into  the  lumen ; 
these  modifications  are  less  pronounced  in  the  veins  than  in  the  arteries, 


506  THE  EEPKODUCTIVE  SYSTEM 

The  tunica  albuginea  and  trabeculae  of  the  corpus  spongiosum  arc 
formed  by  less  dense  connective  tissue  than  is  found  in  the  corpora 
cavernosa  penis,,  and  their  venous  spaces  are  not  so  broad.  The  broad 
anterior  end  of  the  corpus  spongiosum  forms  almost  the  entire  body 
of  the  glans  penis,  being  only  indented  beneath  the  corona  by  the  conical 
anterior  ends  of  the  corpora  cavernosa  penis  which  in  this  part  are 
blended  together  to  form  a  single  median  mass.  The  urethral  canal 
occupies  the  axis  of  the  corpus  spongiosum  from  its  bulb  forward  to 
the  urinary  meatus  at  the  tip  of  the  glans  penis.  This  canal  has  already 
been  described  in  the  preceding  chapter.  It  should  be  recalled  that  its 
lining  epithelium  differs  in  the  several  segments,  being  transitional  in 
its  prostatic  and  membranous  portions,  and  stratified  columnar  through- 
out the  greater  length  of  the  spongy  portio'n,  changing  to  stratified 
squamous  in  the  dilated  fossa  navicularis  of  the  glans  penis. 

The  skin  of  the  glans  penis  is  peculiar  in  the  relatively  moist  char- 
acter of  its  epidermis  and  the  consequent  imperfect  development  of  its 
superficial  horny  layer.  Its  dermal  papillae  are  conspicuously  developed. 
In  the  region  of  the  corona  the  derma  contains  a  ring  of  large  sebaceous 
glands,  the  preputial  glands,  which  open  on  the  free  epithelial  surface. 
Their  secretion  forms  the  smegma,  a  peculiarly  odoriferous  sebum.  The 
so-called  glands  of  Tyson  are  shallow,  non-glandular  epithelial  pockets 
opening  near  the  frenulum  preputii  (Lewis). 

The  medullated  sensory  nerves  (dorsal  nerves  of  the  penis;  branches 
of  the  pudic)  are  abundantly  supplied  with  special  nerve  end-organs. 
In  the  skin  they  form  free  varicose  endings  among  the  epithelial  cells, 
and  are  connected  with  tactile  corpuscles  of  Meissner  in  the  dermal 
papillae.  Deeper  in  the  skin  are  many  end  bulbs  of  Krause,  while  still 
deeper  are  the  peculiar  genital  corpuscles.  Naked  fibrils  pass  to  the 
mucosa  of  the  urethra.  Pacinian  corpuscles  are  also  found  in  the  loose 
connective  tissue  and  in  the  tunica  albuginea  of  the  corpora  cavernosa. 
Sympathetic  nerve  fibers  are  abundantly  supplied  to  the  walls  of  the 
blood-vessels  and  to  the  smooth  muscle  of  the  erectile  tissue.  Branches 
from  the  third  and  fourth  sacral  nerves  also  enter  the  penis  as  the 
nervi  erigentes,  supposed  to  convey  the  impulse  to  erection  as  vasodilator 
fibers. 

The  lymphatics  of  the  penis  form  an  abundant  superficial  set  in  the 
subcutaneous  tissue;  these  follow  the  larger  blood-vessels  and  empty 
into  the  inguinal  lymph  glands.  A  less  abundant  deep  set  of  lymphatics 
in  the  erectile  tissue,  also,  accompanies  the  blood-vessels  of  these  parts, 
but  is  distributed  to  the  pelvic  lymph  glands. 


THE  FEMALE  REPRODUCTIVE  ORGANS  507 


THE  FEMALE  REPRODUCTIVE   ORGANS 

This  system  includes  the  ovaries,  oviducts,  uterus,  vagina,  and  ex- 
ternal genitals.  All  of  these  organs  are  concerned  in  the  reproductive 
function,  the  ovary  producing  the  germ  cell  or  ovum,  and  the  oviduct 
providing  a  suitable  site  for  its  maturation  and  fertilization  and  the 
uterus  for  the  later  development  of  the  resulting  embryo. 

INTERNAL  GENITAL  ORGANS 
The  Ovary 

The  ovary  also  is  properly  regarded  as  a  gland  with  a  double  func- 
tion, namely  cytogenic  and  endocrin.  The  specific  cells  involved  in  the 
production  of  the  internal  secretion  (exclusive  of  the  lutein  substance) 
are  in  doubt.  As  in  the  testis,  the  possibilities  include  the  germ  cells, 
the  general  connective  tissue  and  the  interstitial  cells,  homologues  of 
the  interstitial  cells  of  Leydig  of  the  testis.  The  genetic  and  functional 
relationship  between  the  several  types  of  cells  are  similar  to  those 
described  for  the  testis.  The  ovary,  however,  apparently  does  not  contain 
a  homologue  of  the  Sertoli  cells.  As  in  the  testis  the  internal  secretory 
activity  of  the  ovary  sustains  a  reciprocal  relationship  to  other  internally 
secreting  glands  and  in  some  manner,  directly  or  indirectly,  underlies 
normal  development  and  the  sexual  instinct.  The  ovary,  moreover, 
periodically  elaborates  still  another  internal  secretion. 

The  organ  involved  is  a  transient  structure,  the  corpus  luteum  of 
pregnancy.  This  will  be  described  below.  Its  function  pertains  to 
an  inhibition  of  ovulation  during  pregnancy  (Loeb;  Pearl),  and  a 
stimulation  to  secretory  activity  of  the  mammary  glands  (Bouin  et 
Ancil;  Ott  and  Scott),  and  apparently  in  part  also  to  the  preparation 
of  the  uterine  mucosa  for  proper  implantation  and  normal  develop- 
ment of  the  fertilized  ovum.  As  shown  by  extirpation  experiments  the 
internal  secretions  of  both  ovary  and  testis  influence  also  the  nervous 
system,  and  seem  essential  to  normal  nervous  function. 

The  ovary  is  a  solid  ovoid  body,  about  one  and  one-half  inches 
long,  three-quarters  of  an  inch  wide  and  one-half  inch  thick.  It  is 
attached  to  the  margin  of  the  broad  ligament  posteriorly  by  a  short, 
thick  connective  tissue  pedicle,  the  mesovarium,  which  transmits  the 
blood-vessels  with  which  the  ovary  is  richly  supplied.  At  its  ovarian 
attachment  the  mesovarium  becomes  continuous  with  the  connective 


508 


THE  REPRODUCTIVE  SYSTEM 


tissue  stroma  of  the  ovary.     The  indentation  which  is  thus  produced 
is  known  as  the  liilum. 

The  substance  of  the  ovary  is  divisible  into  a  central  medulla  which 
reaches  the  surface  only  at  the  hilum,  and  a  peripheral  cortex  which 
invests  all  other  portions  of  the  medulla  and  is  in  turn  clothed  by  a  layer 
of  germinal  epithelium,  a  continuation  of  the  peritoneal  epithelium, 
whose  cells  in  this  area  are  peculiar  in  that  they  possess  a  typically 
cuboidal  shape,  and  are  thus  sharply  distinguished  from  the  flattened 
mesothelial  cells  of  the  surrounding  portions  of  the  peritoneum. 


Young 


ru 


Primary 

^-ovarian  follicle 
™*     Antrumfoll.culi 
'of  ffraafiaa 
follicle 


niseis) 


FIG.  449.  —  SECTION  OF  OVARY  OF  ADULT  CAT,  THROUGH  HILUS,  SHOWING  FIVE 

VESICULAR    (GRAAFIAN)   FOLLICLES,   WITH   THE   CUMULUS   OOPHORUS   AND  THE 

ENCLOSED  OVUM. 

The  antrum  folliculi  is  filled  with  a  granular  material,  a  coagulum  of  the  liquor 

folliculi.    Note  that  the  ovarian  follicles  are  in  the  cortical  portion,  the  medulla 

containing  no  follicles.   X7. 

The  Medulla.  —  The  medulla  of  the  ovary  consists  of  a  fibromuscular 
stroma  and  large  numbers  of  blood-vessels.  Its  arteries  are  characterized 
by  their  spirally  tortuous  course  and  thick  muscular  walls;  its  veins  are 
numerous  and  large,  and  their  endothelium  rests  almost  directly  upon 
the  fibromuscular  stroma.  This  portion  of  the  ovarian  stroma  consists 
of  fibrous  connective  tissue  in  which  are  elastic  fibers  and  considerable 
numbers  of  smooth  muscle  cells.  The  connective  tissue  is  richly  sup- 
plied with  cellular-  elements,  most  of  which  are  ovoid  or  fusiform  in. 
shape. 

The  Cortex.  —  The  cortex  of  the  ovary  likewise  contains  a  vascular 
stroma  and  also  large  numbers  of  ova  which  are  in  all  stages  of  develop- 


THE  FEMALE  EEPRODUCTIVE  ORGANS 


509 


ment,  from  the  genetic  cells  of  the  germinal  epithelium  up  to  the  more 
mature  germ  cells,  contained  within  epithelial  sacs  and  known  as  ovarian 
follicles.  During  the  menstrual  epoch  the  ovaries  also  contain  peculiar 
yellowish  bodies,  corpora  lutea,  resulting  from  the  rupture  of  the  largest 


FIG.  450. — FROM  THE  OVARIAN  CORTEX  OF  AN  INFANT,  SHOWING  MANY  OVA  IN 
THE  PRIMARY  FOLLICULAR  STAGE. 

The  portion  above  and  to  the  right  is  near  the  free  surface;  that  below  and  to 
the  left  adjoins  the  medulla.    Hematein  and  eosin.    Photo.     X  200. 

follicles,  a  phenomenon  which  marks  the  climax  of  the  process  of  ovula- 
tion. 

The  stroma  of  the  ovarian  cortex  is  a  connective  tissue  structure 
which  contains  relatively  few  elastic  fibers  and,  except  near  the  medulla, 
very  little  if  any  smooth  muscle.  It  is,  however,  abundantly  supplied 
with  connective  tissue  cells  of  large  si/e,  most  of  which  are  ovoid,  fusi- 
form, or  even  considerably  elongated  in  shape.  Many  of  these  cells 


510  THE  REPRODUCTIVE  SYSTEM 

closely  simulate  smooth  muscle  on  superficial  examination,  but  are 
readily  distinguished  by  careful  study,  especially  if  specimens  are  pre- 
pared by  the  various  differential  staining  methods. 

In  the  vicinity  of  the  follicles  the  stroma  is  specially  rich 
in  cellular  elements  and  is  otherwise  modified  to  form  a  concentric  coat 
for  each  of  these  bodies.  This  coat,  the  theca  folliculi,  consists  of  (a] 
an  outer  layer,  or  tunica  externa,  composed  chiefly  of  connective  tissue 
whose  interlacing  bundles  are  concentrically  disposed,  (&)  an  inner 
layer,  tunica  interim,  which  is  peculiarly  rich  in  large  ovoid  cells,  and 
(c)  an  innermost  membrana  propria,  upon  which  the  epithelial  cells  of 
the  follicle  directly  rest. 

At  the  surface  of  the  ovary  the  cortical  stroma  forms  a  dense  layer 
of  fine  connective  tissue  fibers  whose  delicate  bundles  interlace  in  a 
close-meshed  network.  This  layer,  which  immediately  underlies  the 
germinal  epithelium  at  the  surface  of  the  ovarian  cortex,  is  known  as 
the  tunica  albuginea.  It  differs  greatly  in  thickness  in  different  mam- 
malian species,  in  different  individuals  of  the  same  species,  and  even 
in  different  portions  of  the  same  ovary.  Its  deeper  surface  blends  in- 
sensibly with  the  underlying  stroma  of  the  cortex. 

The  general  appearance  of  the  ovary  varies  according  to  the  number, 
size,  and  stage  of  development  of  its  ova  and  their  follicles.  At  birth 
the  cortex  is  packed  with  large  numbers  of  newly  formed  ova,  all  of  which 
are  in  approximately  the  same  stage  of  development.  Their  number 
has  been  estimated  at  between  30,000  and  70,000.  No  new  ova  are 
formed  after  birth.  Since  in  the  normal  sexual  cycle  from  puberty 
to  the  menopause  (from  about  the  thirteenth  to  the  forty-fifth  year), 
a  period  of  about  32  years,  only  about  400  eggs  are  liberated,  the  vast 
majority  of  potential  ova  must  degenerate.  This  process  of  degeneration 
is  especially  active  after  the  climacteric. 

During  childhood  the  formation  of  larger  follicles  goes  forward 
at  an  unequal  rate,  some  ova  rapidly  approaching  maturity,  others  ap- 
parently remaining  almost  stationary,  and  still  others  undergoing  retro- 
grade development,  so  that  at  the  age  of  puberty  the  ovary  contains 
germ  cells  and  follicles  in  all  stages  of  development.  After  puberty 
the  ripe  follicles  successively  rupture  and  result  in  the  formation  of 
many  corpora  lutea  which  promptly  degenerate,  and  are  finally  replaced 
by  dense  connective  tissue  in  the  form  of  small  scar-like  masses  known  as 
the  corpora  albicantia.  Hence  throughout  the  menstrual  epoch  the  ova- 
rian cortex  contains  many  corpora  lutea  and  corpora  albicantia  in  addition 
to  O7ra  and  follicles  in  various  earlier  stages  of  development.  After  the 


THE  FEMALE  REPRODUCTIVE  ORGANS 


511 


climacteric  the  remaining  follicles  degenerate  and  the  process  of  ovulation 
gradually  ceases. 

We  shall  now  discuss  the  structure  of  the  ovum  or  female  germ  cell 
and  shall  then  successively  trace  its  development  and  maturation,  the 
formation  of  its  vesicular  (Graafian)  follicle,  the  rupture  of  the  follicle, 
and  the  subsequent  history  of  the  corpus  luteum. 

The  Ovum. — The  ovum  is  a  spherical  cell  of  large  size  (200  to 
300  p.).  When  fully  developed  it  is  surrounded  by  a  thick  layer  of 
exoplasm,  the  zona  pellucida,  which  is  probably 
derived  from  the  cytoplasm  of  the  follicular  epi- 
thelium by  which  the  ovum  is  closely  invested. 
The  ovum  itself  consists  of  a  mass  of  cytoplasm, 
the  vitellus,  and  a  large  vesicular  nucleus  or 
germinal  vesicle,  within  which  is  frequently  a 
single  prominent  nucleolus  or  germinal  spot.  The 
cytoplasm  of  the  mature  ovum  is  inclosed  by  a 
very  delicate  cell  membrane,  known  as  the  vitelline 
membrane,  which  is  not  demonstrable  in  the  prim- 
itive ova  of  the  younger  follicles. 

The  CYTOPLASM  of  the  ovum  at  first  appears 
finely  reticular,  but  as  its  development  advances 
a  fatty  material  is  deposited  within  its  meshes, 
usually  in  the  form  of  minute  irregular  spheroids, 
by  the  accumulation  of  which  the  reticular  cyto- 
plasm is  in  great  part  replaced  by  a  granulofatty 
mass  of  faint  yellowish  color  known  as  deuto- 
plasm.  Frequently  this  metamorphosis  is  not 

quite  complete,  a  remnant  of  the  original  cytoplasm  persists  beneath  the 
vitelline  membrane  and  in  the  vicinity  of  the  nucleus. 

Xumerous  cytoplasmic  structures  have  been  described  in  these  cells, 
chief  among  which  are  the  accessory  nucleus  (Nebenkern),  and  the  yolk 
nucleus  (Dotterkern).  The  accessory  nuclei,  occasionally  chromatinic 
and  therefore  basophil,  more  frequently  stain  with  cytoplasmic  dyes  and 
are  at  times  attached,  at  other  times  separate  from  the  true  nucleus. 
They  are  more  probably  remnants  of  mitotic  spindles.  The  yolk  nuclei 
of  mammalian  ova  most  frequently  take  the  form  of  crescentic  masses 
of  lightly  staining  chromatin  ('chrornidia')  which  partially  surround  the 
nucleus,  forming  a  so-called  nuclear  cap.  They  are  often  found  in 
various  stages  of  disintegration,  and  the  fragments  may  be  transported 
to  the  peripheral  portions  of  the  cytoplasm,  or  may  be  irregularly  scat- 


FIG.  451 . — OVTTM,  CON- 
TAINING A  YOLK 
NUCLEUS  (DOTTEK- 
KERN)  AT  THE  LEFT 
AND  ABOVE  THE  NU- 
CLEUS. 

The  peripheral  nuclei 
are  derived  from  the 
adjacent  stroma.  Iron- 
hematoxylin.  Highly 
magnified.  (After  von 
Skrobansky.) 


512  THE  KEPKODUCTIVE  SYSTEM 

tered  as  small  round  chromatic  granules,  which  occur  throughout  the 
cytoplasm.  The  physiological  interpretation  of  these  bodies  is  uncertain. 

The  NUCLEUS  of  the  ovum  is  a  large  spheroidal  vesicle,  the  volume 
and  distribution  of  whose  chroinatin  is  subject  to  great  variation.  Chro- 
ma tin  is  present  in  greatest  amount  during  the  period  of  most  active  cell 
growth,  in  which  the  cytoplasm  of  the  ovum  is  enormously  increased  in 
volume.  At  this  time  the  nucleus  often  appears  as  a  solid  mass  of  chro- 
matin.  Later  the  chromatin  is  diminished  in  volume,  portions  of  its  sub- 
stance being  possibly  extruded  into  the  surrounding  cytoplasm:  the 
nucleus  then  acquires  a  characteristic  vesicular  appearance. 

The  nuclear  membrane  is  sharply  defined  and  is  at  most  times 
prominent,  except,  as  in  other  cells,  during  mitosis,  a  process  which 
marks  the  final  maturation  of  the  germ  cell.  The  nuclear  matrix  or 
nuclear  sap  abounds  in  the  vesicular  type  of  nucleus  and  the  chromatin 
is  scattered  in  small  particles  which  adhere  to  the  inner  surface  of  the 
nuclear  wall  or  to  the  delicate  achromatic  linin  threads. 

Each  ovum  as  a  rule  contains  a  single  nucleus  (germinal  vesicle), 
though  occasionally  two  nuclei  occur.  The  latter  condition  is  presumed 
to  arise  either  by  the  fusion  of  two  ova  within  a  single  follicle  or  from 
incomplete  cell  division  during  development. 

Each  nucleus,  during  its  vesicular  stage,  usually  contains  a  single 
nucleolus  (germinal  spot),  which  forms  a  spherical  mass  of  chromatin, 
situated,  like  the  nucleus  itself,  eccentrically  rather  than  centrally.  The 
staining  properties  of  the  nucleoli  vary  remarkably.  Usually  they  take 
the  basic  (nuclear)  dyes  to  a  greater  or  less  depth;  occasionally  they 
exhibit  an  affinity  for  the  acid  (cytoplasmic)  dyes;  still  other  nuclei  take 
a  metachromatic  or  irregular  tint  with  the  ordinary  nuclear  stains. 
Many  nuclei  even  in  the  absence  of  mitosis  contain  no  nucleolus. 

In  the  development  of  the  ovum  from  the  germinal  epithelium,  whose 
cells  from  their  homology  with  the  spermatogonia  have  been  termed 
oogonia,  there  occur  several  mitoses  which  result  in  so-called  oocytes; 
these  later  develop  into  the  mature  ovum.  At  about  the  time  of  its 
extrusion  from  the  ripe  follicle  a  final  series  of  mitoses  occur,  which  dis- 
tinguish the  maturation  of  the  ovum.  In  this  process  there  is  a  series  of 
two  mitoses  which  result  in  the  appearance  of  the  polar  bodies  and  pro- 
duce a  reduction  in  the  number  of  chromosomes  to  one-half  the  number 
which  is  characteristic  of  the  somatic  cells.  By  the  first  mitosis  the 
cell  produces  what  may  be  termed  a  daughter  ovum,  together  with  the 
first  polar  body,  a  minute  cell  of  insignificant  size.  A  second  mitosis 
ensues  giving  origin  to  the  mature  ovum  or  ootid  and  the  second  polar 


THE  FEMALE  REPRODUCTIVE  ORGANS 


513 


body.  The  egg  now  contains  only  one-half  the  specific  number  of  chromo- 
some.-: the  full  specific  number  is  restored  at  fertilization  by  the  addition 
of  the  male  reduced  complement,  carried  l»y  the  sperm. 

Development  of  the  Ovarian  Follicle. — The   development   of   the 
ovarian  follicle  goes  hand   in  hand   with  that  of  the  ovum  and  can  be 
readily  followed  in  ovaries  from  individuals  of  different  ages,  children 
ft  5fr          JC 


FIG.  452. — FROM  A  SECTION  OF  THE  OVARIAN  CORTEX  OF  A  NEW-BORN  KITTEN. 

K,  Pfliiger's  tubes;  Ke,  germinal  epithelium;  m,  mitosis;  Sir,  ovarian  stroma; 
Ub,  primitive  follicles.     Moderately  magnified.     (After  Kolliker.) 

and  adults,  the  ripe  follicles  and  corpora  lutea  appearing  only  after 
puberty.  The  process  begins  in  the  germinal  epil helium  in  which  certain 
cells  so  increase  in  size  that  they  may  be  readily  distinguished  as  future 
ova.  As  noted  above,  it  is  still  an  open  question  whether  the  primordial 
germ  cells  are  genetic  derivatives  of  the  germinal  epithelium  or  specific 
sex  cells  which  have  wandered  into  and  become  mingled  with  the  cells  of 
the  peritoneal  epithelium.  More  frequently,  however,  the  earliest  step  in 
the  process  consists  in  the  growth  of  solid  cell  columns  from  the  layer 
of  germinal  epithelium  into  the  cortical  stroma  of  the  ovary.  These 
cell  columns  are  kno\vn  as  J'/liiyer's  tubes,  though,  except  occasionally 
at  the  extreme  surface  of  the  organ,  they  lack  a  true  tubular  form  and 
possess  no  vestige  of  a  lumen.  Felix,  however,  concludes  that 
cords  do  not  occur  in  the  human  female. 


514 


THE  REPRODUCTIVE'  SYSTEM 


Certain  cells  in  these  columns,  by  their  increased  size  and  prominent 
nucleus,  become  very  early  distinguishable  as  the  primitive  ova  ;  their 
differentiation  is  rapidly  followed  by  the  constriction  of  the  columns, 
through  the  activity  of  the  surrounding  tissue  of  the  stroma,  in  such 
manner  that  one,  rarely  two  or  more  ova.  and  several  undifferentiated 
epithelioid  cells  are  included  in  each  portion  whose  connection  with  the 


FIG.  4-53. — A  PRIMARY  OVARIAN  FOLLICLE  OF  THE  HUMAN  OVARY. 

From  within  outward  are  seen  the  germinal  spot,  germinal  vesicle,  vitellus,  vitel- 
line  membrane,  zona  pellucida,  granule  cell  layer,  membrana  propria,  and  theca 
folliculi.  The  ovarian  stroma  forms  the  border  of  the  figure.  Hematein  and  eosin. 
Photo.  X  575. 


layer  of  germinal  epithelium  is  thus  severed.  In  this  way  the  print  it  ire 
follicles  ('egg  nests')  are  formed.  In  the  ovary  of  the  new-born  hun- 
dreds of  such  primary  follicles  occur  in  all  portions  of  the  cortex  (Fig. 
450).  They  are  also  found  persistent  in  large  numbers  in  the  ovary  of 
the  adult. 

Many  follicles  never  go  beyond  this  primary  stage  of  development, 
but  after  a  time  undergo  retrograde  metamorphosis  either  by  gradual 
atrophy  or  by  a  process,  known  as  atresia  of  the  follicle,  in  which  the 


THE  FEMALE  REPKODUCTIVE  ORGANS 


515 


chromatolysis  in  the  ovum  and  its  surrounding  follicular  cells  is  followed 
by  growth  and  organization  of  the  theca  folliculi,  the  connective  tissue 
which  is  thus  formed  finally  replacing  the  atretic  follicle. 


FIG.  454. — A  VESICULAR  (GRAAFIAN)  FOLLICLE  OF  THE  HUMAN  OVARY,  SOMEWHAT 
MORE  ADVANCED  THAN  THE  PRECEDING. 

The  accumulation  of  liquor  folliculi  has  separated  the  granular  cells  into  a  discus 
proligerus  and  a  membrana  granulosa.  The  membrana  propria  is  very  sharp,  and 
the  theca  folliculi  is  almost  divisible  into  an  inner  cellular  and  an  outer  fibrous 
layer.  Hematein  and  eosin.  Photo.  X  460. 

After  remaining  stationary  for  a  long  period,  often  for  years,  certain 
of  the  primitive  follicles  enter  upon  a  period  of  rapid  growth.  This 
process  first  affects  the  ovum  and  results  in  the  appearance  of  the  deuto- 
plasm,  xona  pellucida,  and  other  accessory  structures,  as  already  de- 
scribed. Cell  multiplication  now  occurs  in  the  surrounding  epithelial 
cells,  so  that,  iii.-tend  of  the  single  row  of  epithelium  which  surrounds 
the  ovum  of  the  primitive  follicle,  the  ripening  follicle  soon  acquires 


516 


THE  REPRODUCTIVE  SYSTEM 


a  layer  of  follicular  epithelium  several  cells  deep.     This  may  be  desig- 
nated the  mantle-layer. 

The  rapid  multiplication  of  the  epithelial  cells  is  soon  followed  by 
active  secretion,  resulting  in  the  formation  of  a  clear  fluid  by  which 
the  cells  are  more  and  more  separated,  and  the  cytoplasm  of  adjacent 


FIG.  455. — A  NEARLY  RIPE  GRAAFIAN  FOLLICLE  FROM  THE  OVARY  OF  A  DOG. 

a,  fibrous,  and  b,  cellular  layer  of  the  theca  folliculi;  c,  membrana  propria;  d,  mem- 
brana  granulosa,  which,  as  a  result  of  contraction  during  hardening,  has  retracted 
from  the  membrana  propria,  leaving  a  broad  artificial  space;  E,  liquor  folliculi; 
/",  discus  proligerus;  g,  zona  pellucida;  /;,  vitelline  membrane;  i,  vitellus;  k,  the  ger- 
minal spot,  lying  within  the  germinal  vesicle.  Hematein  and  eosin.  Photo.  X  150. 


cells  is  then  readily  seen  to  be  firmly  joined  together  by  numerous  deli- 
cate processes  which  may  be  regarded  as  intercellular  bridges.  Similar 
processes  unite  the  neighboring  cells  to  the  zona  pellucida  which  has 
already  formed  about  the  ovum. 

The  accumulation  of  the  fluid  liquor  folliculi  within  the  follicle  soon 
appears  to  tear  apart  certain  of  the  epithelial  cells,  and  a  fluid-filled  space. 


THE  FEMALE  REPRODUCTIVE  ORGANS  517 

the  ant  rum  folUculi,  is  thus  formed.  Such  a  follicle  is  known  as  a  vesicu- 
lar or  Graafian  follicle.  Follicles  intermediate  between  the  primary  folli- 
cles with  a  single  or  double  layer  of  mantle  cells  and  vesicular  follicles 
may  for  convenience  be  called  intermediate  or  growing  follicles.  The 
epithelial  cells  are  separated  by  the  antrum  into  two  layers:  the  one, 


FIG.  456. — PHOTOMICROGRAPH  OF  A  SECTION  OF  CAT'S  OVARY,  SHOWING  Two  PRI- 
MARY FOLLICLES  AND  ONE  VESICULAR  FOLLICLE. 

adherent  to  the  mcmbrana  propria  of  the  follicle,  is  known  as  the  mem- 
brana  or  strain  m  (jnniulosum;  the  other,  adherent  to  the  zona  pellucida 
of  the  ovum,  is  designated  the  discus  proligerus.  The  two  layers  remain 
in  contact  at  one  point,  and  as  the  liquor  folliculi  increases  in  volume, 
the  attached  discus  proligerus  with  its  contained  ovum  comes  to  occupy 
a  more  and  more  eccentric  position,  and  the  cells  of  the  stratum  granulo- 
sum,  where  the  two  layers  are  in  contact,  appear  to  pile  up  about  the 


518  THE  REPRODUCTIVE  SYSTEM 

ovum  in  the  form  of  a  hillock,  the  so-called  cumulus  oophorus.  The 
latter  term  is  now  generally  used  exclusively  in  a  sense  to  include  and 
displace  the  term  discus  proligerus. 

The  cells  of  the  cumulus,  which  adjoin  the  zona  pellucida,  become 
somewhat  elongated  and  in  this  way  they  form  a  radiate  investment  con- 
sisting of  one  or  two  rows  of  columnar  cells  which  surround  the  zona 
pellucida  of  the  ovum  and  are  known  as  the  corona  radiata.  With  the 
increase  of  the  liquor  folliculi  the  cumulus  with  its  contained  ovum  is 
soon  separated  from  its  attachment  to  the  stratum  granulosum  and  the 
development  of  the  folliculi  is  complete. 

During  this  period  of  rapid  growth  and  development  the  follicle 
has  increased  in  size  from  a  diameter  which  scarcely  exceeded  that  of  its 
ovum  (about  300 /*)  to  such  a  size  that  it  occupies  the  entire  breadth  of 
the  ovarian  cortex.  It  is  now  ready  for  the  final  steps  in  the  maturation 
of  its  ovum  and  for  the  rupture  of  the  follicle  coincident  with  the  ap- 
proach of  the  menstrual  period. 

The  forces  which  lead  to  the  rupture  of  the  follicle  are  not  fully 
determined.  They  are  undoubtedly  varied,  and,  in  addition  to  the 
gradual  attentuation  of  the  layer  of  cortical  stroma  which  covers  the 
free  surface  of  the  follicle  and  is  known  as  the  stigma,  they  include  the 
gradual  accumulation  of  liquor  folliculi  under  increasing  tension,  the 
marked  congestion  of  the  ovary  at  the  approach  of  the  menstrual  period, 
which  is  accompanied  by  the  determination  of  an  undue  proportion  of 
blood  to  the  theca  of  the  ripe  follicle  (Clark),  and  possibly  the  contrac- 
tion of  the  smooth  muscle  contained  in  the  stroma  of  the  deeper  part  of 
the  cortex  and  adjacent  portions  of  the  medulla.  In  any  event,  as  a 
result  of  the  independent  or  combined  action  of  these,  or  other  unknown 
forces,  the  follicle  ruptures  in  the  direction  of  least  resistance,  viz.,  at 
the  attenuated  stigma,  and  the  liquor  folliculi  gushes  forth,  carrying 
with  it  the  detached  ovum  invested  with  its  cumulus.  The  ovum  is 
now  free  to  enter  the  oviduct  and  prepare  itself  for  fertilization  and  the 
development  of  the  future  embryo. 

The  ovum  finds  its  way  from  the  abdominal  cavity  into  the  oviduct  by 
aid  of  currents  established  in  the  direction  of  the  orifice  by  the  cilia  of 
the  cells  covering  the  fimbriae;  perhaps  assisted  by  a  direct  grasping 
activity  on  the  part  of  the  fimbriae.  Since  spermatozoa  are  free  to  wan- 
der out  of  the  oviduct  into  the  abdominal  cavity,  and  since  an  egg  may 
occasionally  fail  to  reach  the  opening  of  the  oviduct,  the  possibilities  are 
offered  for  an  abdominal  pregnancy,  a  result  occasionally  consummated. 
Likewise  an  egg  may  fail  to  become  expelled  from  its  follicle  and  may 


THE  FEMALE  REPEODUCTIVE  ORGANS  519 

then  become  fertilized  within  the  ovary;  or  an  egg  fertilized  in  the  ab- 
dominal cavity  may  perhaps  subsequently  become  implanted  in  an  empty 
follicle.  Development  proceeding  under  such  conditions  results  in  an 
ovarian  pregnancy,  at  least  seven  well  authenticated  cases  being  now  on 
record  (Bryce,  Kerr  and  Teacher,  "An  Early  Ovarian  Pregnancy," 
1908).  Ovarian  pregnancies  cannot  proceed  normally,  and  may  early 
call  for  surgical  intervention.  Occasionally  a  follicle  may  contain  more 
than  one  ovum,  bi-  and  triovular  follicles  being  common.  Such  follicles 
apparently  present  the  possibilities  for  ordinary  twinning  and  multiple 
births.  Arnold  (Anat.  Rec.,  6,  11,  1912)  records  follicles  in  the  ovary 
of  a  negress  also  with  from  four  to  ten  oocytes,  and  one  each  with  eleven 
and  thirteen  oocytes. 

The  following  table  is  offered  for  the  benefit  of  the  student  as  a 
resume  of  the  several  structural  layers  of  the  ripe  Graafian  follicle.    The 
structures  are  enumerated  in  order  from  without  inward: 
f  tunica  externa 

1.  Theca  folliculi  J  tunica  interna 

[membrana  propria. 

2.  Stratum  (seu  membrana)  granulosum. 

3.  Liquor  folliculi — occupying  the  antrum  folliculi. 

4.  Discus  proligerus — cumulus  oophorus. 

5.  Corona  radiata. 

6.  Zona  pellucida  (seu  striata). 

7.  Perivitelline  space  (possibly  an  artifact). 

8.  Vitelline  membrane. 

9.  Vitellus — egg  cytoplasm. 

10.  Nucleus  or  germinal  vesicle. 

11.  Xucleolus  or  germinal  spot. 

The  Corpus  Luteum. — The  rupture  of  the  follicle  is  accompanied 
by  sudden  relief  of  the  intrafollicular  tension  and  consequent  hemorrhage 
from  the  thin-walled  capillaries  of  the  theca  folliculi.  Thus  the  cavity 
of  the  follicle  is  filled  with  blood;  the  ruptured  follicle  is  then  known 
as  a  corpus  hemorrhagicum.  This  is  the  first  stage  in  the  formation  of 
the  corpus  luteum. 

Promptly  succeeding  the  formation  of  the  corpus  hemorrhagicum, 
lutein  cells  appear  at  the  periphery  of  the  body.  They  are  large,  ovoid 
or  polyhedral  cells  having  a  clear  finely  granular  cytoplasm  and  a  peculiar 
yellow  color  due  to  the  presence  of  a  pigment  known  as  lutein.  More- 
over, the  cytoplasm  of  the  lutein  cells  becomes  very  rapidly  infiltrated 
with  droplets  of  fat,  likewise  deeply  colored  by  the  lutein  pigment  which 


520 


THE  KEPKODUCTIVE  SYSTEM 


is  apparently  held  in  solution.  The  origin  of  these  cells  is  still  a  matter 
of  controversy.  By  certain  observers  they  have  been  thought  to  result 
from  the  growth  and  multiplication  of  those  cells  of  the  stratum  granu- 
losum  which  remain  after  the  rupture  of  the  follicle  (Bischoff,  Pfliiger, 
Sobotta)  ;  by  others  they  are  derived  from  the  connective  tissue  cells  in 
the  tunica  interna  of  the  theca  folliculi  (Kolliker,  His,  Palladino). 
Teacher  (1908)  interprets  his  preparations  to  'indicate  quite  clearly  that, 


^»» 


.„    • 


FIG.  457.— SECTION  THROUGH  THE  PERIPHERAL  PORTION  OF  A  CORPUS  LUTEUM, 
SHOWING  LUTEIN  CELLS. 

a,  the  fibrous  coat  of  the  corpus  luteum;  b,  lutein  cells  with  bands  of  newly  formed 
connective  tissue;  c,  central  blood  clot,  partially  organized.  Moderately  magnified. 
(After  Williams.) 


whatever  the  source  of  the  cells  may  be  in  lower  animals,  they  do  not  in 
man  arise  from  the  membrana  granulosa.'  Lutein  cells  may  multiply 
by  mitosis. 

The  lutein  cells  increase  rapidly  both  in  number  and  in  size,  and 
gradually  encroach  upon  the  margin  of  the  blood  clot  whose  progressive 
absorption  precedes  the  advance  of  the  lutein  cells.  But  not  only  does 
the  lutein  mass  grow  centralward,  it  also,  and  especially  in  the  event  of 
fertilization  of  the  discharged  ovum  with  the  consequently  increased 


THE  FEMALE  EEPKODUCTIVE  ORGANS 


521 


vascularity  of  the  reproductive  organs,  grows  at  the  periphery  and  in 
this  way  greatly  increases  the  diameter  of  the  corpus  luteum. 

Minute  vascular  sprouts  of  embryonic  connective  tissue  now  pene- 
trate the  lutein  mass  from  the  adjacent  stroma  of  the  theca  folliculi, 
and  growing  centralward  in  septa-like  processes,  finally  penetrate  as  far 
as  the  central  blood  clot.  Hence  the  corpus  luteum  at  this  stage  presents 
a  more  or  less  radiate  structure.  The  central  ends  of  the  embryonic 
connective  tissue  septa  frequently 
unite  to  inclose  the  remnant  of  the 
central  blood  clot,  or  by  further 
proliferation  they  may  entirely  re- 
place the  clot  by  a  mass  of  newly 
formed  gelatinous  connective  tissue. 

The  absorption  of  the  blood  clot 
usually  proceeds  slowly.  Remnants 
of  the  disintegrating  blood  in  the 
form  of  a  central  stellate  mass, 
which  often  contains  hematoidin 
crystals,  frequently  persist  until  the 
corpus  luteum  has  become  well  or- 
ganized with  connective  tissue. 

The  formation  of  new  connec- 


FIG. 458. — PORTION  OF  CORPUS  LUTE- 
UM OF  PIG. 


tive  tissue  is  followed  by   its   con-  Gr.l.c.,  granulosa  lutein  cells;  th.c., 

traction.      That   this  process  occurs  theca  lutein  cells;  b.v,  blood  vessel 

....                      .  '      ..  In  the  pig  the  corpora  lutea  are  formed 

very  early  in  the  connective  tissue  chiefly  from  granulosa  cells,  in  small 


first  formed  at  the  periphery  of  "the 


part  also  from   theca   cells,    x    1000. 
(After  Corner,  Am.  Jour.  Anat.,  vol. 
body,  may  possibly  be  held  to  ac-     26,  1919). 

count  for  the  fatty  infiltration  and  final  degeneration  of  the  lutein  cells, 
because  of  the  consequent  interference  with  their  vascular  supply. 

By  continued  development  the  entire  mass  of  lutein  cells  is  gradually 
replaced  by  connective  tissue,  which,  by  further  contraction,  finally  pro- 
duces a  dense  white  fibrous  scar,  no  longer  containing  lutein  pigment, 
known  as  a  corpus  albicans.  This  body  persists  for  a  long  period,  but 
undergoes  progressive  contraction  until  only  a  minute  scar  of  almost 
microscopical  size  remains  to  mark  the  site  of  the  ruptured  corpuscle 
and  the  highly  developed  corpus  luteum.  Such  scars  persist  for  years 
in  the  stroma  of  the  ovarian  cortex. 

Finally  it  must  be  stated  that  there  are  no  recognizable  histological 
differences,  other  than  those  of  sixc  and  duration,  between  the  corpora 
lutea  vera  of  pregnancy  and  the  corpora  lutea  spuria  whose  formation 


522 


THE  EEPEODUCTIVE  SYSTEM 


accompanies  the  extrusion  of  the  unfertilized  ovum.  The  true  corpora 
lutea  are  of  relatively  large  size  and  persist  for  many  months,  the 
spurious  are  somewhat  smaller  and  persist  for  little  more  than  one 
month;  yet  both  pass  through  the  same  histological  process  of  develop- 
ment and  degeneration  and  both  leave  their  scars  in  the  substances  of 
the  ovarian  stroma. 

Ovarian  scars  also  arise  through  atresia  of  the  larger  follicles,  the 
degeneration  of  whose  epithelium  is  followed  by  an  ingrowth  of  tissue 
derived  from  the  theca  folliculi,  and  the  gradual  development,  organiza- 


FIG.  459. — A  CORPUS  ALBICANS,  FROM  A  SECTION  OF  THE  HUMAN  OVARY. 
X  75.     (After  Williams.) 

tion,  and  final  contraction  of  the  connective  tissue,  forming,  as  it  were, 
a  minute  but  imperfect  corpus  albicans,  in  the  center  of  which  is  often 
the  shrunken  degenerating  remains  of  the  ovum.  Certain  small  acido- 
philic  homogeneous  bodies,  the  so-called  Call-Exner  bodies,  of  uncertain 
significance  are  also  occasionally  present  in  the  stratum  granulosa  of  the 
ovarian  follicles. 

Blood  Supply. — The  blood-vessels  of  the  ovary  are  derived  from  the 
branches  of  the  ovarian  and  iiterine  arteries.  These  vessels  enter  the 
ovary  through  the  mesovarium  and  divide  into  numerous  branches  which 
pursue  a  peculiar  spiral  or  corkscrew  course  through  the  stroma  of  the 
medulla,  and  finally  enter  the  cortex.  They  possess  thick  muscular 
walls  containing  bundles  of  longitudinal  smooth  muscle  fibers.  In  the 
cortex  they  supply  capillaries  to  the  stroma,  and  in  the  theca  folliculi  of 
the  Graafian  follicles  they  form  rich  plexuses  of  broad  capillaries  and 


THE  FEMALE  REPRODUCTIVE  ORGANS 


523 


thin-walled  venules. 
As  the  follicle  ap- 
proaches maturity 
these  plexuses  be- 
come enormously  de- 
veloped and  appar- 
ently bear  an  impor- 
tant relation  to  the 
rupture  of  the  fol- 
licle and  the  rapid 
development  of  the 
corpus  luteum.  The 
veins,  which  take 
origin  from  the  ven- 
ules  of  these  capil- 
lary plexuses,  con- 
verge toward  the 
medulla,  where  they 
form  a  plexus  of 
large  thin-walled 
vessels,  the  plexus 
venosus  ovarii  or 
pampiniform  plexus, 
which  is  embedded 
in  the  connective 
tissue  of  the  medul- 
la, the  mesovarium, 
and  the  adjacent 
portions  of  the  broad 
ligament. 


FIG.  460. — FROM  A  THICK  SECTION 
OF  THE  OVARY  OF  A  WOMAN. 

The  blood-vessels  have  been  in- 
jected. A,  a,  and  a',  arteries;  b,  cor- 
pus luteum,  partially  organized;  c, 
point  where  rupture  of  the  follicle 
occurred;  d,  tangential  section  of  a 
follicle;  e,  corpora  lutea  which  have 
organized  and  are  already  retrogres- 
sive. (After  Clark.) 


y  ,-.._, 


FIG.  461. — TRAXSECTIONS  OF  THE  HUMAN  OVIDUCT. 

A,  uterine;  B,  isthmic;  and  C,  ampullar  portions.     X  15.     (After  Williams.) 

524 


THE  FEMALE  REPRODUCTIVE  ORGANS 


525 


The  lymphatics  arise  in  the  cortical  stroma  by  anastomosing  canals 
and  capillaries  of  irregular  caliber,  which  are  especially  abundant  in 
the  walls  of  the  Graalian  follicles.  These  vessels  converge  toward  the 
medulla,  where  they  enter  lymphatics  which  are  supplied  with  valves, 
and  find  their  way  to  the  lymph  nodes  of  the  pelvic  aiid  lumbar  regions. 

The  nerves  are  chiefly  derived  from  the  ovarian  sympathetic  plexus. 
They  enter  the  hilum  and  are  distributed  to  the  walls  of  the  blood- 
vessels, and  to  the  stroma  of  the  ovary ;  here  they  form  a  rich  terminal 
plexus  in  the  walls  of  the  follicles.  Whether  or  not  the  naked  fibrils  are 
distributed  to  the  epithelial  cells  within  the  follicle  has  not  been  satis- 
factorily determined.  The  small  ganglia  of  the  medulla  include  also 
pheochrome  cells  (Winiwarter)  ;  and  certain  sensory  fibers  are  said  to 
end  in  lamellar  corpuscles. 

The  Oviduct 

The  oviduct,  uterine  tube,  or  Fallopian  tube  is  a  narrow  duct  about 
4%  inches  long, 
leading  from  the 
ovary  to  the  cavity 
of  the  uterus.  It 
consists  of  a  broad, 
funnel  -  shaped, 
fringed  or  finibri- 
atcd  extremity  (or 
infundibulum),  a 
constricted  neck, 
an  intermediate 
ampulla  of  consid- 
erable diameter, 
and  a  slender  isth- 
mus by  which  the 
oviduct  communi- 
cates with  the  ute- 
rine cavity. 

Throughout  the 
entire  tube  its  wall, 
which  becomes 
gradually  thinner 

from  isthmus  to  iiifiiii<lil>tilimi,  consists  of  ilnvc  coats — mucous,  mus- 
cular and   serous — Inil    the  character  of  its  mucous  membrane  differs 


FIG.  462. — FROM  A  TRANSECTION  OF  THE  AMPULLA  OF  THE 
OVIDUCT,  SHOWING  THK  STRUCTURE  OF  THE  MUCOSA. 
X  280.  (After  Williams.) 


526  THE  BEPRODUCTIVE  SYSTEM 

somewhat  in  its  several  portions.  In  the  isthmus  it  is  relatively  smooth 
and  usually  presents  four  longitudinal  ridges  which  have  few  secondary 
or  accessory  folds ;  in  the  ampulla  the  mucosa  is  greatly  folded,  the  pri- 
mary ruga?  possessing  small  secondary  folds  which  extend  in  all  direc- 
tions, and  by  their  very  complexity  nearly  obliterate  the  otherwise  broad 
lumen.  In  the  fimbriated  portion  the  folds  of  the  mucosa  are  continued 
into  the  fimbrise,  at  the  margin  of  which  the  columnar  ciliated  epithe- 
lium of  the  oviduct  becomes  directly  continuous  with  the  serous  mesothe- 
lium  of  the  peritoneum  investing  the  outer  surface  of  the  tube. 

The  mucosa  is  lined  by  columnar  epithelium,  arranged  either  in  a 
simple  or  pseudo-stratified  manner,  the  greater  portion  of  whose  cells 
are  provided  with  cilia.  The  ciliary  motion  is  directed  toward  the  uterus. 
The  epithelial  layer  covers  all  the  folds  of  the  mucosa  and,  extending 
deeply  into  the  crevices,  forms  invaginations  which,  in  transections  of 
the  tube,  simulate  glandular  structures.  There  are,  however,  no  true 
secreting  glands  in  the  oviduct.  Here  and  there  groups  of  non-ciliated 
cells  with  clear  cytoplasm  occur  among  the  more  numerous  ciliated  cells 
of  the  mucosa. 

The  epithelium  rests  upon  a  thin  homogeneous  basement  membrane 
beneath  which  is  a  tunica  propria  consisting  of  a  cellular  type  of  connec- 
tive tissue.  Many  of  the  connective  tissue  cells  are  of  fusiform  shape, 
and,  unless  specially  stained  or  carefully  examined,  they  closely  resemble 
smooth  muscle  cells.  The  mucosa,  however,  contains  no  muscle  except  at 
the  bases  of  the  largest  folds,  into  which  occasional  fibers  from  the  adja- 
cent muscular  coat  penetrate. 

The  muscular  wall  of  the  oviduct  is  formed  by  two  layers  of 
smooth  muscle — a  broad  inner  circular  layer,  and  an  outer  longitudinal 
coat,  which  is  very  unequally  developed  at  different  portions  of  the  cir- 
cumference, but  is  relatively  thin  in  all  parts,  and  is  entirely  wanting  at 
frequent  intervals.  The  outer  layer  is  usually  broadest  at  the  free  mar- 
gin of  the  oviduct  and  at  its  opposite  side  where  the  tube  is  attached  to 
the  broad  ligament.  The  inner  circular  fibers  are  more  or  less  obliquely 
disposed,  and,  toward  the  mucosa,  the  muscular  bundles  fuse  insensibly 
with  the  cellular  connective  tissue  of  the  mucous  membrane.  In  gen- 
eral the  inner  circular  layer  is  thickest  at  the  isthmus  and  thinnest  at 
the  infundibulum,  while  the  longitudinal  layer  is  thickest  toward  the 
fimbriated  end. 

The  serous  coat  of  the  oviduct  is  continuous  with  the  peritoneum. 
It  consists  of  an  outermost  layer  of  mesothelium  which  rests  upon  a  sub- 
epithelial  layer  of  connective  tissue,  by  which  it  is  firmly  united  to  the 


THE  FEMALE  REPRODUCTIVE  ORGANS 


52? 


muscular  wall.     This  portion  of  the  serous  coat  contains  the  larger 
vessels  and  nerves,  which  are  distributed  to  the  inner  coats. 


FIG.  463. — TRANSECTION  OF  THE  UTERUS  OF  AN  APE. 

a,  mucosa;  6,  circular  muscle;  c,  longitudinal  muscle;   d,  serous  coat;  e,   lateral 
ligament;  /,  Wolffian  tube;  g,  blood-vessels.     X  4.     (After  Sobotta.) 


Blood  Supply. — The  arteries  of  the  oviduct  are  derived  from  the 
uterine  and  ovarian  vessels.  The  larger  divisions  find  their  way  through 
the  connective  tissue  of  the  serosa  whence  they  send  smaller  branches 
inward  to  form  a  plexus  between  the  layers  of  the  muscular  wall  and 
among  the  bundles  of  circular  muscle  fibers.  From  this  plexus  capillaries 


528  THE  REPRODUCTIVE  SYSTEM 

are  distributed  to  the  muscular  coat,  and  to  the  mucous  membrane  in 
which  they  form  a  rich  subepithelial  capillary  plexus.  The  veins  follow 
a  similar  course,  and  like  the  arteries,  form  an  extensive  plexus  in  the 
muscular  coat.  The  abundance  of  vessels  in  the  muscular  wall  of  the 
oviduct  has  led  to  the  description  of  this  coat  as  the  vascular  layer  of 
the  organ. 

The  lymphatics  arise  by  anastomosing  plexuses  in  the  mucosa,  from 
which  vessels  pass  to  the  serous  coat  and  enter  valved  lymphatics  by 
which  the  lymph  is  conveyed  to  the  lymph  nodes  of  the  lumbar  region. 

The  nerves,  which  are  chiefly  sympathetic,  are  distributed  from  a 
plexus  in  the  serous  coat,  to  the  muscular  wall,  and  to  the  mucosa,  in 
which  they  form  a  terminal  subepithelial  plexus. 

The  Uterus 

The  uterus  is  a  hollow  pear-shaped  organ,  divisible  into  a  deepest  or 
fundus  portion,  the  body,  and  the  cervix,  about  3  inches  in  depth,  l1/^ 
in  width  and  1  in  thickness.  The  cervix  opens  into  the  body  through 
the  internal  os,  into  the  vagina  through  the  external  os.  Its  wall  consists 
of  a  mucous  membrane,  a  muscular  coat,  and  an  outermost  serous  coat 
which  is  derived  from  the  peritoneum  and  invests  the  body  of  the  organ. 
The  cervix  uteri  projects  into  the  vaginal  canal  and  the  serous  coat  is 
there  replaced  by  a  reflection  of  the  vaginal  mucosa. 

The  serous  coat,  or  perimetrium,  of  the  uterus  consists  of  meso- 
thelium  which  rests  upon  a  thin  subepithelial  layer  of  connective  tissue. 
It  presents  no  peculiarities. 

The  muscular  coat,  or  myometrium,  of  the  uterus  consists  of 
smooth  muscle  whose  fibers  are  of  large  size  (40  to  60  p.  in  length)  and 
which  are  disposed  in  interlacing  bundles.  In  the  lower  mammals  these 
form  quite  regular  layers — an  outer  longitudinal,  a  thick  inner  layer, 
most  of  whose  fibers  are  circular,  and  an  innermost,  but  less  distinct, 
submucous  portion  containing  oblique  and  longitudinal  fibers.  The  outer 
longitudinal  and  circular  layers  are  separated  by  a  fibromuscular  stratum 
containing  a  rich  plexus  of  large  blood-vessels. 

In  the  human  uterus  the  arrangement  of  muscle  fibers  is  much  less 
regular,  but  follows  a  similar  plan,  though  there  is  no  distinct  sub- 
division into  layers.  Nevertheless,  careful  examination  reveals  three  indis- 
tinct strata  which  are  intimately  blended  with  one  another.  The  outer- 
most of  these  indistinct  layers  consists  of  irregularly  disposed  longitudi- 
nal fibers,  the  stratum  supravasculare.  This  layer  is  in  most  parts  very 


THE  FEMALE  REPRODUCTIVE  ORGANS 


529 


thin,  and  is  best  developed  opposite  the  margin  of  the  lateral  ligament 
and  in  the  cervix  uteri.  Within  this  is  a  broad  layer  of  interlacing 
bundles  of  more  or  less  circular  fibers,  which,  from  the  slight  obliquity 
of  their  course,  frequently  cross  each  other  at  acute  angles.  Inter- 
mingled with  these  circular  bundles  are  many  large  blood-vessels,  from 
which  both  the  mucous  and  muscular  coats  are  supplied.  This  broad 
middle  layer  is  therefore  known  as  the  stratum  vasculare.  The  inner 


FIG.  464. — TRANSECTION  THROUGH  THE  BODY  OF  THE  HUMAN  UTERUS. 

g,  blood-vessels;  I,  lumen;  II,  broad  ligament;  Im,  longitudinal  muscle;  m,  circular 
muscle  (the  fibers  are  mostly  oblique);  s,  serous  coat;  tp,  mucosa.  Hematoxylin 
and  eosin.  X  2.  (After  Sobotta.) 

portion  of  this  second  layer  passes  insensibly  into  a  thin  innermost 
stratum  submucosum,  which  again  contains  many  longitudinal  fibers, 
and  upon  which  the  mucosa  directly  rests. 

The  uterine  mucosa,  or  endometrium,  is  of  considerable  thickness 
(1  to  3  mm.).  It  is  clothed  with  epithelium,  and  its  tunica  propria  con- 
tains numerous  tubular  glands. 

The  epithelium  is  of  the  ciliated  columnar  type,  and  consists  of  a 
single  row  of  cells.  Apparently  not  all  of  its  cells  are  provided  with 
cilia,  areas  of  ciliated  alternating  with  groups  of  non-ciliated  epithelium. 
The  epithelial  layer  is  continuous  with  the  epithelium  of  the  uterine 
glands;  in  the  region  of  the  external  os  uteri  it  is  replaced  by  the  strati- 
fied squamous  epithelium  of  the  vaginal  mucosa.  Ofttimes,  and  espe- 


530 


THE  REPRODUCTIVE  SYSTEM 


cially  in  multipart,  the  stratified  squamous  epithelium  of  the  vagina  is 
continued  for  some  little  distance  within  the  canal  of  the  cervix  uteri; 
it  never  clothes  more  than  the  lower  one-half  to  two-thirds  of  the  cervical 
canal.  The  current  resulting  from  the  vibration  of  the  intra-uterine 
cilia  is  directed  toward  the  vagina. 

The  tunica  propria  of  the  mucosa  consists  of  a  peculiar  embryonal 
type  of  connective  tissue,  similar  to  that  of  the  oviducts,  which  contains 
very  few  collagenous  and  no  elastic  fibers,  but  which  is  richly  supplied, 


FIG.  465. — FROM  A  TRANSECTION  OF  THE  UTERINE  MUCOSA. 
X  16.     (After  Williams.) 


in  fact  is  literally  packed,  with  cellular  elements.  These  cells  are  ovoid 
or  fusiform  in  shape,  and  many  of  them  are  branched ;  their  nuclei,  also, 
are  ovoid  and  somewhat  vesicular.  Many  lymphocytes  are  found  in  the 
tunica  propria,  but  these  mostly  occur  in  the  vicinity  of  the  lymphatics 
and  smaller  blood-vessels  with  which  the  uterine  mucosa  is  abundantly 
supplied.  In  the  mucosa  of  the  cervix  uteri  the  development  of  the  con- 
nective tissue  appears  to  be  more  advanced,  the  cellular  elements  being 
relatively  fewer;  it  also  contains  many  fine  fibers  which  appear  to  form 
a  delicate  network.  At  the  external  os  uteri  the  tunica  propria  is  con- 


THE  FEMALE  REPRODUCTIVE  ORGANS 


531 


tinuous  with  the  similar,  though  still  more  fibrous,  layer  of  the  vaginal 
mucosa. 

The  uterine  glands  are  divisible  into  two  types — those  of  the  body  of 
the  organ,  and  those  of  its  cervix.  The  former  are,  perhaps,  to  be  re- 
garded as  tubular  imaginations  of  the  lining  epithelium,  whose  function 


FIG.  466. — FROM  THE  CERVIX  UTERI  OF  A  GIRL  OF  SIXTEEN  YEARS,  SHOWING  THE 
CERVICAL  GLANDS  IN  SECTION. 

a-a,  lining  epithelium.    Hematein  and  eosin.    Photo.     X  102. 

is  one  of  epithelial  regeneration  rather  than  of  glandular  secretion.    The 
tubules  of  the  cervix  uteri  are  true  mucus:secreting  glands. 

The  uterine  glands  proper,  those  of  the  body  of  the  organ,  are  slightly 
branched  or  forked  tubules  which  traverse  the  entire  breadth  of  the 
mucosa,  presenting  a  characteristic  spiral  or  corkscrew  course;  their 
blind  extremities  are  often  bent  or  turned  to  one  side,  apparently  from 
the  proximity  of  the  adjacent  muscular  coat.  The  glandular  epithelium 


532 


THE  REPKODUCTIVE  SYSTEM 


is  of  the  columnar  type  and,  like  that  of  the  free  surface,  is  frequently 
provided  with  cilia,  especially  near  the  mouth  of  the  gland.  The  epithe- 
lium rests  directly  upon  the  connective  tissue  of  the  tunica  propria. 

The  cervical  glands  (glandule  uterince  cervicales)  resemble  those  of 
the  body  of  the  organ  in  their  tubular  form  and  the  columnar  shape  of 

their  epithelium,  but  here  the  re- 
semblance ceases.  The  cervical 
glands  are  much  branched,  and  their 
tubules  present  frequent  dilatations, 
some  of  which,  apparently  from  oc- 
clusion of  their  outlet,  attain  a 
macroscopic  size,  and  are  then 
known  asNalothian  follicles  (ovula 
Nabothii) ;  they  are  filled  with  a 
tenacious  mucous  secretion.  The 
glandular  epithelium  near  the  crypt- 
like  ducts  is  usually  ciliated,  like 
that  of  the  surface,  but  in  the 
secreting  portions  it  consists  of  tall, 
clear,  columnar  cells  which  are  in 
various  stages  of  secretory  activity, 
their  product  being  a  viscid  glairy 
mucus,  strings  and  granules  of 
which  are  found  within  the  lumen 
of  the  glands,  as  well  as  within  the 
canal  of  the  cervix  uteri. 

The  uterine  cavity  is  a  relative 
term.  In  the  virgin,  the  mucosa  is 
considerably  folded  and  its  surfaces 
are  almost  in  apposition,  being  only 
separated  by  a  very  limited  amount 
of  desquamated  epithelium  and  cel- 
lular debris,  to  which,  in  the  canal 
of  the  cervix  uteri,  the  mucous  secretion  is  added.  During  pregnancy, 
the  development  of  the  fetus  within  the  uterine  cavity  distends  its  walls 
and  so  dilates  the  canal  that  it  at  last  forms  a  sac  of  sufficient  size  to 
contain  the  fetus,  which  floats  within  the  amniotic  fluid  inclosed  by  its 
membranes. 

The  blood-vessels  of  the  uterus  enter  through  the  folds  of  the  lateral 
ligament  and  find  their  way,  through  the  subepithelial  connective  tissue 


FIG.  467. — A  GLAND  OF  THE  HUMAN 
CERVIX  UTERI  IN  LONGITUDINAL 
SECTION. 

X90.     (After  Williams.) 


THE  FEMALE  REPRODUCTIVE  ORGANS  533 

of  the  serous  coat  and  the  muscular  wall,  to  all  portions  of  the  organ. 
In  the  vascular  layer  of  the  muscular  coat  they  form  an  extensive  plexus 
from  which  branches  are  distributed  to  the  musculature  and  to  the  mu- 
cosa,  the  branches  to  the  latter  penetrating  nearly  to  the  surface,  where 
they  form  rich,  subepithelial,  capillary  and  venous  plexuses.  The  uterine 
arteries,  like  those  of  the  ovary,  possess  a  peculiar,  spirally  tortuous 
course.  The  veins  accompany  the  arteries,  but  are  less  tortuous. 

The  lymphatics  of  the  uterus  arise  by  anastomosing  channels  in  the 
mucous  and  muscular  coats.  They  form  a  vascular  plexus  in  the  serous 
coat  and  lead  outward,  through  the  lateral  ligaments  and  pelvic  connec- 
tive tissue,  to  the  lower  lymph  nodes  of  the  lumbar  region. 

The  nerves  of  the  uterus  are  very  numerous.  They  include  both 
spinal  and  sympathetic  fibers.  They  enter  the  serous  coat  from  the 
ganglionic  -  pelvic  plexus,  and  are  distributed  to  the  vascular  layer  of 
the  muscular  coat.  They  there  form  a  rich  plexus,  from  which  sympa- 
thetic motor  fibers  are  distributed  to  the  musculature  and  to  the  walls  of 
the  blood-vessels. 

The  distribution  of  nerves  within  the  mucosa  has  not  yet  been 
thoroughly  worked  out.  According  to  von  Gawronsky  (Arch.  f.  Gynakol., 
1894)  and  Kostlin  (Fortschr.  d.  Med.,  1894)  sensory  nerve  fibrils  pene- 
trate nearly  to  the  surface  and  form  a  scanty  subepithelial  plexus,  whence 
are  derived  fibrils  which  terminate  between  the  epithelial  cells. 

Since  the  uterus  is  subject  to  extensive  structural  variations  dependent 
upon  its  functional  phase  and  condition,  it  becomes  important  to  recog- 
nize the  differential  marks  of  the  menstruating  and  of  the  pregnant 
uterus.  Besides  general  histologic  alterations  in  the  wall,  especially  in 
the  mucous  and  muscular  layers,  additional  structures  involved  in  the 
pregnant  uterus  are  the  decidual  cells  and  chorionic  villi;  these  are 
diagnostic  of  pregnancy.  Only  the  histology  of  these  structures  will  be 
here  described ;  for  a  consideration  of  their  embryologic  significance  and 
relationship  reference  must  be  made  to  a  text-book  of  Embryology. 

The  Menstruating  Uterus 

The  appearance  of  the  phenomena  of  menstruation  is  accompanied  by 
decided  alterations  in  the  structure  of  the  uterine  mucosa.  In  spite  of  the 
difficulty  of  obtaining  sufficiently  fresh  and  well  preserved  material,  certain 
changes  which  characterize  the  menstruating  uterus  are  now  definitely 
known.  These  chiefly  consist  in  increased  vascularity,  hypertrophy  of  the 
elementary  tissues  of  the  mucosa,  epithelial  desquamation,  and  rupture  of 
the  blood-vessels,  with  consequent  hemorrhages.  These  changes  are  fol- 


534 


THE  EEPKODUCTIVE  SYSTEM 


lowed  by  a  process  of  regression  and  later  of  regeneration,  by  which  the 
uterine  raucosa  rapidly  returns  to  its  former  condition. 

The  first  or  hypertrophic  stage  involves  the  epithelium,  whose  cells  are 
elongated,  and  the  tunica  propria,  in  which  many  of  the  connective  tissue 
cells  undergo  multiplication  and  enlargement.  Thus  the  mucous  mem- 
brane becomes  greatly  thickened;  its  glands,  also,  are  increased  in  both 
length  and  breadth,  becoming  at  the  same  time  even  more  tortuous  than 
before.  The  glandular  hypertrophy  involves  both  the  uterine  and  the 
cervical  glands;  the  secretion  of  the  latter  is  much  increased. 


FIG.  468. — FROM  A  SECTION  OF  THE  HUMAN  UTERINE  MUCOSA  AT  THE  FIRST  DAY 
OF  MENSTRUATION. 

e,  epithelium;  d,  disintegrating  layer;  g,  gland;  v,  blood-vessel;  m,  muscular  coat. 
X  44.     (After  Minot.) 


At  the  same  time,  the  blood-vessels  become  widely  dilated,  especially 
those  near  the  surface,  and  broad  thin-walled  sinuses  are  formed  beneath 
the  epithelium.  Finally  these  vessels  rupture  and  hemorrhages  occur  into 
the  substance  of  the  mucosa  as  well  as  into  the  cavity  of  the  organ;  des- 
quamation  and  disintegration  of  the  superficial  portions  of  the  mucosa 
result.  The  menses  which  are  thus  formed  contain  blood,  epithelium,  con- 
nective tissue  cells,  and  many  leukocytes,  which  wander  out  from  the  blood- 
vessels of  the  mucosa  in  large  numbers.  The  greatly  thickened  and  hemor- 
rhagic  mucosa  is  known  as  the  decidua  menstrualis. 

Eegression  and  regeneration  follow  rapidly  upon  one  another,  the 
mucosa  gradually  regaining  its  former  condition.  During  this  process  fat 
droplets  appear  in  many  of  the  connective  tissue  cells.  The  epithelium  ia 
rapidly  regenerated,  the  new  cells  arising  from  the  epithelial  remnants  at 


THE  FEMALE  REPRODUCTIVE  ORGANS 


535 


the  mouths  of  the  uterine  glands.  In  the  course  of  a  few  days  the  mucosa 
regains  its  former  quiescent  condition.  The  complete  cycle  includes  28 
days,  of  which  the  menstrual  process  occupies  about  seven. 


The  Gravid  Uterus 

In  the  event  of  conception  the  uterine  changes  are  more  pronounced 
than  during  menstruation.  These  alterations  include  the  same  processes  of 
hypertrophy  and  thickening  as  occur  in  the  decidua  menstrualis;  they  in- 
volve the  musculature  as  well  as  the  mucosa  but  are  not  followed  by  regres- 
sive changes, — hemorrhage,  desquamation,  etc. — until  parturition  occurs. 

The  muscular  wall  undergoes  an 
enormous  increase  both  in  the  num- 
ber and  size  of  its  fibers.  The  rela- 
tively short  (30  to  60  /m)  smooth 
muscle  fibers  of  the  uterine  wall 
gradually  increase  in  size  to  as  much 
as  eleven  times  their  former  length 
and  two  to  five  times  their  breadth 
(Kolliker).  The  connective  tissue  of 
the  muscular  coat  also  increases  in 
volume  and  becomes  more  distinctly 
fibrous.  After  parturition,  fat  drop- 
lets appear  within  the  muscle  cells, 
and  the  muscular  wall  by  gradual 
atrophy  returns  to  its  former  condi- 
tion. 

In  the  mucosa  the  formation  of 
a  decidual  membrane  goes  forward 
in  a  manner  similar  to  the  develop- 
ment of  the  decidua  menstrualis,  but 
the  process  is  exaggerated.  The  tu- 
nica propria  soon  becomes  divisible 
into  two  distinct,  though  not  sharply 

defined,  layers,  a  deeper  cavernous  portion  which  is  permeated  by  broad 
vascular  channels  together  with  the  atrophied  remains  of  the  uterine 
glands,  and  a  superficial  compact  layer  in  which  the  vascular  channels, 
except  for  the  thin-walled  venous  spaces,  are  smaller  and  the  connective 
tissue  cells  more  closely  packed. 

Many  of  the  connective  tissue  cells  attain  a  large  size  and  their  nuclei 
are  frequently  multiple,  or  they  may  acquire  an  irregular  polymorphonu- 
clear  form.  Giant  cells  are  thus  produced  in  the  compact  layer  of  the 
mucosa  of  the  gravid  uterus;  they  are  highly  characteristic  of  this  tissue 
and  are  known  as  decidual  cdls.  Though  it  is  frequently  asserted  that 


FIG.  469. — A  GROUP  OP  DECIDUAL 
CELLS  FROM  THE  HUMAN  UTERUS 
DURING  THE  EARLY  STAGES  OF  PREG- 
NANCY. 

One  of  the  cells  contains  two  nuclei 
and  a  number  of  fat  vacuoles.  Three 
nuclei  of  the  connective  tissue  stroma 
are  also  shown.  X  750. 


536 


THE  EEPEODUCTIVE  SYSTEM 


similar  cells  occur  in  the  decidua  menstrualis,  this  is  denied  by  Minot 
(1903),  who  states  that  in  a  considerable  number  of  menstrual  decidua 
examined,  no  such  cells  were  ever  found. 

The  superficial  epithelium  is  soon  desquamated  and  the  tunica  propria 
comes  into  contact  with  the  fetal  chorion.  The  glandular  epithelium  is 
also  partially  degenerated,  often  becoming  flattened  and  of  irregular  shape. 
It  is  frequently  desquamated  into  the  glandular  lumen;  this  lumen  is  thus 


FIG.  470. — CHORIONIC  VILLI  FROM  THE  HUMAN  PLACENTA  AT  FULL  TERM. 
Hematein  and  eosin.     Photo.     X  114. 

reduced  to  a  narrow  crevice,  which  is  so  elongated  during  the  dilatation  of 
the  uterine  wall  that  the  axis  of  the  glandular  remnant  becomes  nearly 
parallel  to  the  surface  of  the  decidua. 

The  decidual  membrane  which  is  thus  formed  is  divisible  into  three 
portions,  according  to  its  relation  to  the  tissues  of  the  embryo :  1,  that 
portion  upon  which  the  developing  ovum  directly  rests,  which  is  known 
as  the  decidua  serotina  or  decidua  lasalis  but  later  forms  the  placenta 
uterina  or  maternal  portion  of  the  placenta;  2,  at  the  margins  of  the 


THE  FEMALE  EEPEODUCTIVE  ORGANS  537 

implanted  ovum  the  decidual  tissues  close  up  over  the  ovum  which  is 
thus  surrounded  by  the  so-called  decidua  reflexa  or  decidua  capsularis, 
which,  after  the  early  months  of  pregnancy,  is  gradually  obliterated  by  the 
increasing  growth  of  the  fetus,  and  is  finally  replaced,  its  functions  being 
progressively  usurped  by  the  newly  formed  placental  tissues;  3,  all  the 
remaining  portions  of  the  decidual  mucosa,  those  which  line  the  greater 
part  of  the  uterine  cavity,  collectively  form  the  decidua  vera,  with  whose 
surface,  in  the  later  months  of  pregnancy,  the  fetal  chorion  is  intimate  in 
relation. 

The  mucosa   of  the  cervix  uteri  meanwhile  becomes  greatly  hyper- 


A  B  c 

FIG.  471. — CHORIONIC  VILLUS  AT  VARIOUS  STAGES  OF  DEVELOPMENT. 

A,  chorionic  villus  at  third  week;  B,  at  fourth  month;  C,  at  term.     (After  Wil- 
liams.)    X  225. 

trophied  and  its  glands  much  enlarged.  This  portion  of  the  uterine  mucosa 
does  not,  however,  enter  into  the  formation  of  the  decidua  vera;  the 
changes  occurring  in  its  tissues,  though  similar,  are  much  less  pro- 
nounced. 

The  Chorionic  Villi. — These  innumerable  processes  form  the  greater 
portion  of  the  placental  tissues.  They  vary  in  size  from  the  broad  main 
stems  to  the  very  slender  terminal  branches  of  the  floating  villi.  They 
consist  of  a  core  of  mesoderm  covered  with  a  variable  layer  of  ectoderm. 
In  the  early  condition  of  the  placenta  (fourth  or  fifth  month  of  pregnancy) 
the  villi  are  clothed  with  a  double  epithelial  layer,  of  which  the  superficial 
takes  the  form  of  a  syncytium  (plasmoditrophoblast),  while  the  deeper 
consists  of  a  cellular  layer,  the  cells  of  Langhans  (cytotrophoblast).  At 
later  periods  (seventh  month  to  full  term)  the  syncytium  is  found  to  have 
undergone  a  peculiar  alteration,  having  become  much  thinner,  and  having 
even  completely  disappeared  from  considerable  portions  of  the  villi,  it  being 
replaced  by  canalized  fibrin;  at  other  points  the  syncytial  cytoplasm  is 
much  thickened  and  the  nuclei  appear  to  be  bunched  or  grouped  within 
the  thickened  portions;  these  areas  are  known  as  cell-knots  or  proliferation 
islands.  Here  and  there  the  degenerated  cell-knots  have  been  replaced  by 


538 


THE  EEPRODUCTIVE  SYSTEM 


canalized  fibrin.  Wherever  the  main  stems  are  inserted  into  the  decidua 
the  epithelium  which  formerly  covered  their  tips  appears  to  have  also 
degenerated  into  a  peculiar  hyalin  border  zone.  Towards  the  end  of  preg- 
nancy the  cytotrophoblast  becomes  converted  into  plasmoditrophoblast. 

Within  its  syncytium  the  substance  of  the  villus  consists  of  the  super- 
ficial cells  of  Langhans  with  their  large  ovoid  nuclei,  and  a  core  of  con- 
nective tissue  of  a  delicate  embryonic  type,  in  which  are  the  fetal  blood- 
vessels. Even  the  smallest  villi  contain  capillary  loops  of  broad  caliber, 
which  are  supplied  by  fetal  arteries,  derived  from  the  umbilical  arteries, 
which  distribute  their  branches  throughout  the  chorionic  connective  tissue. 
The  fetal  veins  accompany  the  arteries. 

The   Vagina 

The  vagina  is  a  fibromuscular  sheath  whose  wall  is  divisible  into 
three  coats — mucous,  muscular,  and  fibrous. 

The  mucous  membrane  is  clothed  by  a  layer  of  stratified  squamous 
epithelium,  and  is  thrown  into  numerous  folds  or  rugae.  The  epithelium 


FIG.  472.— VAGINAL  MUCOSA.     X  90. 
ep.,  epithelium;  p.,  papilla;  c.t.,  connective  tissue.     (After  Williams.) 

rests  upon  a  fibrous  basement  membrane.  The  tunica  propria  is 
formed  by  a  close-meshed  areolar  tissue  which,  in  its  deeper  and  looser 
portion,  is  permeated  by  vascular  channels  of  considerable  size.  This 
deep  vascular  layer  is  frequently  described  as  a  submucosa;  it  rests 
directly  upon  the  muscular  wall.  The  surface  of  the  mucosa  presents 
numerous  conical  papillae  which  project  well  into  the  epithelial  layer. 
The  musculature  of  the  vagina  contains  smooth  or  involuntary 
fibers,  and  is  divisible  into  an  inner  circular  and  an  outer  longitudinal 
layer.  The  muscle  fibers  are  long  and  slender.  Considerable  connective 


THE  FEMALE  REPRODUCTIVE  ORGANS         *  539 

tissue  is  distributed  among  the  muscle  bundles.  The  latter  are  arranged 
in  more  or  less  parallel  layers  which  are  united  by  the  delicate  bands  of 
conned ive  tissue. 

The  outer  fibrous  coat  consists  of  dense  areolar  tissue  which  is 
well  supplied  with  elastic  fibers.  It  loosely  unites  the  vaginal  wall  to 
the  surrounding  tissues.  In  this  coat  is  a  plexus  of  blood-vessels  and 
lymphatics,  from  which  branches  pass  to  the  muscular  coat,  and  to  the 
mucosa,  in  which  they  form  an  abundant  plexus.  An  extensive  nerve 
plexus,  including  spinal  and  sympathetic  fibers,  among  which  are  many 
small  ganglia,  is  also  found  in  the  fibrous  coat;  it  distributes  motor 
branches  to  the  muscular  wall  and  to  the  blood-vessels,  and  sensory 
fibers  to  the  mucosa,  in  which  they  end  in  relation  with  the  cells  of  the 
lining  epithelium. 

The  vaginal  mucosa  is  reflected  upon  the  outer  wall  of  the  cervix 
uteri,  and  at  or  near  the  external  os  it  is  continuous  with  the  mucosa  of 
the  uterine  cavity.  Though  occasional  glands  have  been  found  in  the 
vaginal  mucous  membrane,  lined  either  by  mucus-secreting  or  by  ciliated 
cells,  these  glands  would  seem  to  be  properly  considered  as  anomalies, 
since  they  are  usually  absent,  the  mucoid  secretions  of  the  vaginal  canal 
being  chiefly  provided  by  the  abundant  supply  of  mucus  from  the  cervical 
glands  of  the  uterus.  The  vaginal  mucosa  is  continuous  below  with  that 
of  the  vestibule. 

The  Vestigial  Structures 

The  vestigial  structures  associated  with  the  female  reproductive  system 
include  the  vesicular  appendage  (hydatid  of  Morgagni),  the  epoophoron, 
and  the  paroophoron.  The  same  general  statements  made  concerning  'the 
male  vestigial  structures  hold  likewise  for  those  of  the  female. 

The  VESICULAR  APPENDAGE  is  attached  to  the  fimbriated  end  of  the  ovi- 
duct, its  stalk  being  continuous  with  the  collecting  duct  of  the  epoophoron. 
It  is  a  globular  pedunculated  structure  of  small  size  (three  to  six  milli- 
meters diameter) ;  it  is  lined  with  cuboidal  epithelium,  and  may  contain 
fluid.  It  represents  the  atrophic  end  of  the  degenerated  'Wolffian  duct. 
There  are  besides  a  variable  number  of  smaller  accessory  vesicular  appen- 
dages attached  to  the  broad  ligament. 

The  EPOOPHORON  (parovarium;  organ  of  Kosenmiiller)  lies  between  the 
layers  of  the  broad  ligament  in  the  triangular  area  between  the  ovary  and 
the  ampulla  of  the  oviduct.  It  consists  of  a  variable  number  of  tubules 
(eighteen  to  twenty),  the  homologues  of  the  ductuli  efferentes  of  the  male. 
These  tubules  may  be  blind  at  only  one  or  at  both  ends ;  they  may  be  lined 
with  ciliated  columnar  epithelium,  or  their  lumina  may  become  obliterated. 


540 


THE  KEPKODUCTIVE  SYSTEM 


Those  blind  only  at  one  end  connect  with  a  longitudinal  duct,  a  variable 
remnant  of  the  Wolffian  duct. 

The  PAROOPHORON — homologue  of  the  male  paradidymis — is  a  more 
mesial  collection  of  similar  tubules  of  like  structure  and  genetic  signifi- 
cance. It  is  said  to  be  present  only  in  infants.  The  further  extension 
mesially  of  the  longitudinal  duct,  either  in  continuation  with  the  collecting 
duct  of  the  epoophoron  or  paroophoron,  or  as  an  isolated  blind  duct,  usually 
in  the  wall  of  the  uterus  and  vagina,  is  known  as  the  canal  of  Gartner.  It 
is  the  vestige  of  the  lower  portion  of  the  fetal  Wolffian  duct. 

THE  EXTERNAL  GENITALS 


The  vestibule  is  supplied  with  a  mucosa  which  offers  a  gradual  tran- 
sition from  the  vagina,  on  the  one  hand,  to  the  skin  on  the  other.     Its 

stratified  squamous  epithe- 
lium becomes  in  this  way 
gradually  more  and  more 
like  that  of  the  skin,  eleidiu 
granules  first,  and  keratin 
later  appearing  on  the  outer 
surface  of  the  labia  minora. 
The  epithelium  of  the  labia 
majora  is  identical  with 
that  of  the  skin. 

The  labia  minora  or 
nymphae  form  the  lateral 
walls  of  the  vestibule  and 
consist  of  a  fold  of  the  mu- 
cosa which  is  provided  with 
exceptionally  tall  papilla?. 
Small  sebaceous  glands 
open  directly  upon  the  sur- 
face of  the  stratified  squam- 


FIG.  473. — TRANSECTION  OF  A  LABIUM  MINUS  OF 
AN  INFANT. 


ous  epithelium.  There  are 
no  hair  follicles  in  relation 
with  these  glands,  and  the 
labia  minora  contain  no 
adipose  tissue.  They  are 

richly  supplied  with  blood-vessels,  and  with  sensory  nerve  endings. 
The  labia  majora    are  formed  by  similar  folds  whose  inner  surface 

resembles  the  adjacent  portion  of  the  labia  minora,  but  whose  outer 


a,  labium  minus;  6,  border  of  the  labium 
rnajus;  c,  adipose  tissue  of  the  latter.  Hematein 
and  eosin.  Photo.  X  12. 


THE  FEMALE  REPRODUCTIVE  ORGANS  541 

surface  is  cutaneous  and  is  supplied  with  sebaceous  and  sudoriparous 
glands  and  with  numerous  hair  follicles.  The  subepithelial  areolar 
tissue  is  very  dense  and  its  deeper  portion  contains  much  fat. 

The  clitoris  consists  of  a  mass  of  erectile  tissue,  homologous  with 
the  corpora  cavernosa  and  glans  penis  of  the  male;  it  is  covered  by  a 
fold  of  the  mucosa.  It  is  well  supplied  with  nerves,  which  terminate 
in  tactile  corpuscles,  end  bulbs,  and  genital  corpuscles.  In  this  vicinity 
also,  as  well  as  in  the  region  of  the  labia,  Pacinian  corpuscles  are  occa- 
sionally found. 

The  hymen  is  formed  by  a  reduplication  of  the  vestibular  mucosa. 
Its  inner  surface  is  similar  to  that  of  the  labia  miuora  and  vagina;  its 
outer  is  like  that  of  the  cutaneous  surface,  except  that  it  contains  no 
hair  follicles. 

The  glandulae  vestibulares  minores  are  a  group  of  small  mucus- 
secreting  glands,  similar  in  structure  to  the  urethral  glands  of  Littre  in 
the  male,  which  occur  in  the  vestibular  mucosa  in  the  vicinity  of  the 
meatus  urethrse. 

.The  glandulae  vestibulares  majores  (glands  of  Bartholin)  form 
a  paired  tubulo-alveolar  mucus-secreting  gland  which  opens  by  a  narrow 
duct  into  the  groove  between  the  hymen  and  labium  minus.  The  tubular 
alveoli  are  lined  by  columnar  mucus-secreting  cells ;  the  ducts  are  clothed 
with  columnar  epithelium,  which,  as  they  approach  their  termination, 
becomes  double-rowed,  and  finally  changes  to  a  stratified  squamous  epi- 
thelium similar  to  that  of  the  surface  upon  which  they  open.  These 
ducts  frequently  present  saccular  dilatations. 

THE  MAMMARY  GLANDS 

From  a  strictly  histogenic  standpoint  the  mammary  glands  should  be 
considered  as  appendages  of  the  skin,  and  as  such  should  more  properly 
have  been  considered  in  the  chapter  devoted  to  that  subject.  Yet  these 
glands  are  so  closely  related  to  the  reproductive  functions,  attaining 
their  full  development  only  in  the  lactating  female,  that  it  seems  equally 
proper  to  consider  them  at  this  time  as  accessory  reproductive  organs. 

The  mammary  glands  may  be  regarded  as  modified  sweat  glands. 
Though  producing  a  fatty  secretion  they  show  no  resemblance  to  seba- 
ceous glands.  The  mammas  undergo  the  same  slight  but  progressive  de- 
velopment in  both  sexes  until  the  time  of  puberty  when  they  suffer 
regressive  changes  in  the  male,  persisting  thereafter  only  in  rudimentary 
condition.  In  the  female  they  continue  to  grow,  but  become  functionally 


542 


THE  REPRODUCTIVE  SYSTEM 


active  only  in  the  event  of  pregnancy.  Upon  the  hemispherical  corpus 
mamma  can  be  distinguished  the  central  raised  >n/>/>le  or  mammilla,  and 
the  surrounding  roughened  and  pigmented  circular  area,  the  areola. 

Each  mammary  gland   consists  of  fifteen   to  twenty  lobes,  each  of 
which  is  of  itself  a  branched  saccular  gland  whose  lactiferous  <hi<-l  opens 


FIG.  474. — FROM  THE  ACTIVELY  SECRETING  MAMMARY  GLAND  OF  A  WOMAN. 

Several  lobules  are  included,     a,  interlobular  duct;  b,  interlobular  connective 
tissue.     Hematein  and  eosin.     Photo.     X  52. 

on  the  surface  of  the  nipple  near  its  apex.  The  main  lactiferous  or  lobar 
ducts  subdivide  in  an  arborescent  manner  into  many  interlobular  ducts, 
about  which  are  clustered  the  groups  of  secreting  alveoli,  each  group 
forming  one  of  the  many  lobules  included  in  a  lobe  of  the  gland.  The 
structure  of  the  lobule,  as  well  as  the  general  appearance  of  microscopi- 
cal sections  of  the  gland,  varies  according  to  the  stage  of  development 
and  the  condition  of  activity  of  the  organ. 


THE  FEMALE  REPRODUCTIVE  ORGANS 


543 


The  Active  Gland.— During  lactation  the  glandular  alveoli  are  so 
numerous  as  to  form  by  far  the  most  prominent  portion  of  the  gland. 
Each  lobule  consists  of  a  cluster  of  saccular  alveoli  which  open  by  short 
alveolar  ducts  into  the  interlobular  ducts  of  the  connective  tissue  which 
invests  the  lobules  of  the  gland.  The  alveoli  are  closely  packed  within 
the  lobule. 

The  actively  secreting  alveoli  are  lined  by  cuboidal  or  low  columnar 
cells  which  vary  much  in  height  even  within  the  same  alveolus,  and  are 
often  considerably  flattened.  Fat  drop- 
lets accumulate  within  the  distal  portion 
of  their  cytoplasm.  The  droplets  in- 
crease, in  size  as  well  as  in  number, 
until  they  finally  occupy  the  greater 
part  of  the  distal  end  of  the  cell  and 
are  separated  from  each  other  by  only 
a  narrow  interval  of  albuminous  cyto- 
plasm. Finally  the  fat  droplets  are 
discharged  into  the  broad  lumen  of  the 
alveolus,  where  they  apparently  still  re- 
tain a  thin  albuminous  envelope  which 
prevents  their  cohesion  and  consequent 
fusion,  and  thus  permits  their  suspen- 
sion in  the  albuminous,  fluid  portion  of 
the  milk.  The  milk  may  include  also 
cytoplasmic  and  nuclear  debris. 

The  spherical  nuclei  of  the  secret- 
ing cells  during  this  process  are  crowd- 
ed to  the  base  of  the  cell,  and  after  the  discharge  of  the  secretion  the 
shrunken  but  nucleated  cell  remnants  remain  in  situ;  after  a  period 
of  rest  the  cells  apparently  resume  their  secretory  function.  It  appears 
probable  that  each  cell  in  its  life  history  may  repeatedly  pass  through 
the  cycle  of  secretory  changes,  though  the  exact  number  of  such  cycles 
which  an  individual  cell  may  present  obviously  does  not  admit  of  dem- 
onstration. 

As  a  rule,  the  active  epithelium  consists  of  a  single  row  of  cells, 
though  here  and  there  they  appear  as  if  piled  upon  one  another  to  form 
a  double  layer.  During  pregnancy  many  of  these  cells  may  be  seen  in 
mitosis.  The  actively  secreting  cells  contain  basal  (ergastoplasmic)  fila- 
ments. According  to  Hoven  (Anat.  Anz.,  39,  1911)  these  filaments 
break  up  into  granules  from  which  minute  fat  spherules  develop.  The 


FIG.  475. — MODEL  OF  A  RECON- 
STRUCTION OF  AN  INTRALOB- 
ULAR  DUCT  AND  ITS  ACINI 
FROM  THE  ACTIVE  MAMMARY 
GLAND  OF  A  WOMAN. 

X  200.     (After  Maziarski.) 


544 


THE  REPRODUCTIVE  SYSTEM 


epithelium  rests  upon  a  reticular  or  homogeneous  hasement  mem- 
brane, within  which  are  occasional  basket  cells.  These  have  been  in- 
terpreted as  smooth  muscle  cells,  similar  to  those  of  the  secretory  por- 
tions of  the  sweat  glands.  The  alveoli  of  the  active  gland  are  so  closely 
packed  that  a  connective  tissue  tunica  propria  is  no  more  than  scarcely 
demonstrable.  The  thin  tunica  propria  is,  however,  richly  supplied 
with  blood  capillaries,  lymphatic  vessels,  and  nerve  fibers. 

The  ducts  of  the  mammary  gland  are  lined  by  either  a  single  or 
double  row  of  low  columnar  cells.  They  possess  a  relatively  broad  lumen. 
Their  membrana  propria  is  supported  by  a  thin  connective  tissue  wall, 


FIG.  476. — ACTIVE  MAMMARY  GLAND  OF  RAmtrr  (22  DAYS  AKTEII  FECUNDATION.) 
The  alveoli  are  filled  with  milk  containing  fat  droplets.   X41G.     (After  L.  Schil.) 


containing  both  circular  and  longitudinal  elastic  fibers  but  no  muscle. 
The  elastic  fibers  of  the  smaller  ducts  are  poorly  developed,  but  in  suit- 
able specimens  the  longitudinal  fibers  are  readily  seen  even  in  very 
small  branches.  Beyond  the  lactiferous  sinus  the  duct  epithelium 
changes  to  a  stratified  squamous  variety  which  is  continuous  with  that 
of  the  .cutaneous  surface  of  the  nipple. 

The  glandular  lobules  are  firmly  united  by  strong  septa  derived  from 
the  dense  areolar  tissue  in  which  they  are  embedded.  In  the  deeper 
parts  of  the  gland  occasional  lobules  of  fat  are  found  in  this  tissue. 
Within  the  nipple  and  beneath  the  adjacent  portions  of  the  areola,  smooth 


THE  FEMALE  REPRODUCTIVE  ORGANS 


545 


muscle  fibers  are  also  found.  These  are  arranged  in  circular  bundles 
at  the  base  of  the  nipple,  with  longitudinal  fibers  within  its  substance 
which,  at  the  base  of  the  mammilla,  di- 
verge  in  radiating  bundles  into  the  sub- 
cutaneous tissue  of  the  areolar  zone.  Con- 
traction of  these  fibers  elevates  and  hard- 
ens the  nipple,  thus  simulating  the  action 
of  the  erectile  tissues. 

According  to  Liperovsky  (Anat.  Anz., 
45,  20,  1914)  elastic  fibers  are  more  abun- 
dant than  was  formerly  recognized  in  the 
walls  of  the  alveoli  and  in  the  interalveo- 
lar  connective  tissue,  frequently  in  inti- 
mate association  with  smooth  muscle  cells. 
Such  'elastico-muscular  apparatus'  is  well 
developed  in  the  peripheral  portion  of  the 
glands,  in  the  subpapillary  layer  of  the 
skin,  and  especially  in  the  vicinity  of  the 
nipple.  The  elastic  fibers,  which  are  super- 
ficially distributed,  appear  embedded  at 
their  deeper  ends  in  the  muscle  fibers. 
This  peculiar  arrangement  of  elastic  fibers 
in  relation  to  smooth  muscle  probably  aids 
in  the  expulsion  of  the  secretion. 

Embedded  in  the  subcutaneous  tissue 
of  the  areola  are  also  a  number  of  small 
accessory  lactiferous  glands  known  as  the 
Glands  of  Montgomery  (Areolar  Glands  of 
Duval).  The  nipple  and  areola  contain 
also  abundant  sebaceous  glands;  and  sweat 
glands  are  present  in  the  periphery  of  the 
areola. 

The  Resting  Gland.— With  the  cessa- 
tion of  lactation  the  glandular  alveoli  un- 
dergo a  rapid  atrophy,  and  are  replaced 
by  connective  tissue  derived  from  the  inter- 
lob  ular  stroma.  The  ducts  contract  and 
the  epithelium  piles  up  to  form  a  two- 
rowed,  or  even  thicker,  layer.  The  alveoli  are  reduced  to  mere  buds 
from  the  terminal  ducts,  and  their  lumen  is  almost  obliterated;  their 


FIG.  477. — FROM  A  SECTION  OP 
THE  HUMAN  MAMMARY 
GLAND  IN  THE  RESTING 
CONDITION. 

a,  remnants  of  the  glandular 
alveoli;  b,  duct;  c,  connective 
tissue;  d,  adipose  tissue.  Hem- 
atein  and  eosin.  Photo.  X  10. 


546  THE  REPRODUCTIVE  SYSTEM 

epithelium  is  similarly  massed  into  a  double  layer  of  small  cells.  The 
lobules  are  reduced  in  size  and  consist  only  of  a  few  shrunken  alveoli 
clustered  about  the  termination  of  an  interlobular  duct.  The  lumen  of 
the  alveoli,  if  any,  contains  no  secretion,  and  that  of  the  ducts,  except 
for  a  little  granular  albuminous  material  and  an  occasional  leukocyte, 
is  empty. 

The  connective  tissue  stroma  is  much  increased  in  volume,  and  in 
places  shows  a  marked  infiltration  with  fat.  The  alveolar  tissue  of  the 
mammary  gland  at  all  times  contains  wandering  leukoc}ies,  and  many 
granule  cells,  both  acidophil  and  basophil  in  character. 

With  the  appearance  of  pregnancy  the  gland  promptly  reenters  a 
state  of  activity;  its  alveoli  multiply;  its  connective  tissue  becomes  rela- 
tively diminished  in  volume;  its  lobules  are  reformed  and  their  alveoli 
finally  begin  secretion,  a  process  which  is  heralded  by  the  formation  of 
a  granulo-fatty  colostrum,  a  rather  serous  fluid  in  which  are  suspended 
large  numbers  of  colostrum  corpuscles,  large  spheroidal  cells,  resembling 
leukocytes  in  their  general  form  and  in  the  character  of  their  nuclei,  but 
which  possess  a  broad  rim  of  cytoplasm  often  containing  numbers  of  fat 
globules  of  varying  size.  Their  cytoplasm  has  also  been  shown  to  contain 
neutrophil  granules  of  Ehrlich  similar  to  those  of  the  polymorphonuclear 
leukocytes  (Michaelis,  Arch.  mikr.  Anat.,  1898). 

Colostrum  discharge  precedes  and  follows  the  period  of  lactation  for 
a  few  days ;  it  appears  also  in  both  sexes  for  several  days  after  birth  when 
it  is  commonly  known  as  'witch's  milk/ 

The  origin  of  the  colostrum  corpuscles  is  still  somewhat  in  doubt, 
though  modern  technic  has  gradually  discredited  the  theory  of  their 
origin  from  desquamated  remnants  of  the  alveolar  epithelium,  and  shows 
them  to  be  more  probably  enlarged  leukocytes  which  have  wandered 
through  the  alveolar  wall  and  have  thus  found  their  way  into  the 
lumen,  where  they  take  on  a  phagocytic  activity  and  continue  their 
growth.  The  following  facts  may  be  mentioned  in  support  of  this  theory : 
a,  leukocytes  can  be  readily  found  between  the  cells  of  the  alveolar 
epithelium  as  well  as  in  the  lumina  of  the  saccules;  ~b,  the  colostrum 
corpuscles  examined  in  a  fresh  condition  on  a  warmed  slide  have  been 
repeatedly  shown  to  possess  the  property  of  ameboid  motion;  c,  the 
colostrum  corpuscles,  when  stained,  present  the  same  granular  and  non- 
granular  varieties  as  do  the  leukocytes  of  the  blood;  d,  finally,  the 
colostrum  corpuscles  have  been  shown  to  undergo  mitotic  cell  division 
(Bizzozero  and  Ottolenghi),  a  phenomenon  which  AVC  should  hardly  ex- 
pect to  find  in  degenerated  and  desquamated  epithelial  cell  remnants. 


THE  FEMALE  REPRODUCTIVE  ORGANS  547 

The  blood-vessels  of  the  mammary  gland  are  specially  ahundant. 
They  form  rich  capillary  plexuses  about  the  walls  of  the  active  alveoli. 
Many  of  the  venules  coming  from  these  plexuses  converge  toward  the 
areola,  where  they  form  an  incomplete  venous  circle  (circulus  venosus  of 
Holler)  from  which  the  efferent  veins  take  their  origin. 

The  lymphatics  of  the  mammary  gland  are  also  numerous.  They 
take  origin  from  broad  channels  among  the  alveoli  and  enter  a  rich  plexus 
about  the  interlobular  ducts.  From  here  several  vessels  pass  to  the  lymph 
nodes  of  the  axilla. 

The  nerves  of  the  mammary  gland  include  both  spinal  (sensory)  and 
sympathetic  fibers.  The  latter  are  distributed  to  the  vascular  walls,  to 
the  smooth  muscle  of  the  areola  and  nipple  and  to  the  alveolar  epithe- 
lium. The  sensory  fibers  supply  the  connective  tissue  of  the  nipple  and 
areola  where  they  occasionally  terminate  in  tactile  and  Pacinian  cor- 
puscles. 

Among  the  secreting  alveoli  the  nerve  fibers  form  an  epilemmal 
plexus  beneath  the  membrana  propria,  from  which  fibrils  penetrate  be- 
tween the  epithelial  cells,  upon  which  they  end  in  minute  granular 
varicosities  (Arnstein,  Anat.  Anz.,  1895). 

Milk.— Milk,  secreted  by  the  active  mammary  gland,  consists  of  an 
emulsion,  in  which  fat  droplets,  varying  in  size  from  two  to  twenty 
microns  or  more,  are  suspended  in  a  watery  albuminous  fluid.  Water 
constitutes  about  eighty -six  per  cent,  of  the  secretion;  the  protein  con- 
stituent (three  per  cent.),  which  is  largely  nuclein,  is  derived  in  part 
from  degenerating  nuclei.  Milk  contains  also  a  small  amount  of  sugar 
(five  per  cent.)  and  a  trace  of  salt.  Each  fat  droplet  is  presumably 
invested  with  a  thin  coat  of  casein,  derived  from  the  cytoplasm  of  the 
secreting  epithelium.  Occasionally  leukocytes  occur  in  the  milk,  but 
never  in  large  numbers,  and  like  the  similar  colostrum  corpuscles,  they 
are  mostly  confined  to  the  earlier  periods  of  lactation. 


CHAPTER    XVI 

THE  DUCTLESS   GLANDS— ENDOCKIN  GLANDS 
(Organs  of  Internal  Secretion] 

Under  this  heading  it  will  be  convenient  to  consider  the  suprarenal, 
thyroid,,  parathyroid,  thymus,  carotid,  and  coccygeal  glands,  the  hypoph- 
ysis cerebri,  the  epiphysis  cerebri  and  the  paraganglia.  This  group 
of  organs  properly  includes  also  the  pancreatic  islets,  the  interstitial 
cells  of  the  testis  and  the  ovary,  and  the  corpora  lutea  already  described. 


I.     THE    SUPRARENAL   GLANDS 

THE  SUPRARENAL  GLANDS  (bodies  or  capsules;  also  called  adrenals] 
are  two  flattened  irregular  glandular  masses  situated  close  to  the  cranial 
extremity  of  each  kidney,  but  without  organic  or  genetic  relationship 
with  the  renal  system.  On  section  the  adrenal  is  seen  to  be  readily 
divisible  into  a  bright  yellow  or  brownish-yellow  cortex  and  a  more 
vascular,  and  hence  darker  and  somewhat  reddish,  medulla,  whose  central 
portion  transmits  several  large  veins  which  make  their  exit  from  an 
indentation  in  the  anterior  surface  of  the  organ,  known  as  the  hiluin. 

Development  and  Function. — The  suprarenal  gland  is  a  composite 
structure  formed  by  the  intimate  association  of  two  embryologieally  dis- 
tinct anlages:  one,  the  cortical  component,  of  mesodennal,  the  other  or 
medullary  component,  of  ectodermal  origin.  The  cortical  component  arises 
as  a  series  of  buds  from  the  celomic  epithelium  covering  the  medial  upper 
surface  of  the  cephalic  third  of  the  Wolffian  body;  the  medulla  develops 
from  cells  which  have  migrated  from  the  abdominal  sympathetic  plexus 
(celiac  plexus),  and  which  elaborate  peculiar  granules  having  an  affinity 
for  chromium,  hence  called  chromaffin  (or  plieochrome]  cells.  The  onto- 
genetic  process  recapitulates  almost  precisely  the  phylogenetic  history  of 
the  suprarenals :  In  fishes  the  homologues  of  the  two  mammalian  com- 
ponents remain  separate,  and  the  cortical  representative  includes  a  series 
of  bodies,  the  interrenal  ~bodies  or  organs;  the  medullary  representative, 

548 


THE  SUPRARENAL  GLANDS  549 

also  comprising  a  series  of  structures,  is  known  throughout,  due  to  its 
close  topographical  relationship  to  the  kidney,  as  the  adrenal.  The  cortex 
of  the  mammalian  suprarenal  gland  thus  represents  the  product  of  fusion 
of  the  ichthyoid  interrenals.  In  the  groups  between  fishes  and  mammals, 
the  association  of  interrenals  (cortical  component)  and  adrenals  (medul- 
lary component)  becomes  progressively  more  intimate. 

The  suprarenal  is  absolutely  essential  to  life;  removal  promptly  results 
in  death.  -According  to  Crile  (1914)  the  brain  is  intimately  dependent 
upon  the  suprarenals;  when  both  glands  are  excised  in  the  rabbit  death 
follows  in  eighteen  hours,  the  brain  cells  meanwhile  exhibiting  loss  of 
chromophilic  substance.  The  two  portions  are  believed  to  have,  in  part  at 
least,  a  different  function,  both  inhering  however  in  an  internal  secretion. 
The  cortex  is  generally  believed  to  elaborate  an  antitoxic  secretion  for 
neutralization  of  harmful  products  of  destructive  metabolism.  The  func- 
tion of  the  medulla  is  dependent  upon  the  adrenalin  (adrenin;  epinephrin) 
of  the  pheochrome  granules,  probably  having  to  do  with  maintaining  the 
proper  tonus  of  the  muscle  of  the  heart  and  blood-vessels,  thus  underlying 
blood  pressure.  Minute  amounts  of  epinephrin  in  the  blood  effect  a  sensi- 
tization  of  the  vasoconstrictor  nerve  endings  so  that  the  efferent  impulses 
discharged  cause  the  muscular  coats  of  arterioles  to  contract  vigorously, 
the  result  being  an  increase  in  blood  pressure.  The  most  conspicuous 
diseases  of  the  suprarenals  involve  hypersecretion,  perhaps  inducing  to 
arteriosclerosis;  and  hyposecretion,  frequently  the  result  of  tuberculous 
lesions,  producing  a  clinical  complex  known  as  Addison's  disease.  (Refer- 
ence should  be  made  to  Vincent's  "Internal  Secretions  and  the  Ductless 
Glands,"  Longmans,  1912.) 

The  organ  is  enclosed  by  a  connective  tissue  capsule  of  considerable 
thickness.  From  the  inner  surface  of  the  capsule  delicate  fibrous  trabecu- 
Ise  pass  inward  and  subdivide  the  epithelial  parenchyma  of  the  organ 
into  cell  groups  and  columns,  which  vary  in  their  appearance  according  to 
the  distribution  of  the  connective  tissue  trabeculae.  The  suprarenal  paren- 
chyma is  exceptionally  prone  to  post  mortem  changes.  In  the  medulla 
the  connective  tissue  presents  an  irregular  areolar  arrangement;  the 
more  regular,  though  varying  form  of  the  areolae  in  the  cortex,  subdi- 
vides this  portion  of  the  organ  into  three  more  or  less  distinct  layers, 
which  were  first  described  by  Arnold  (Arch.  f.  path.  Anat.,  1866)  as  the 
zona  glomerulosa,  zona  fasciculata,  and  zotia  reticularis. 

In  the  zona  glomerulosa  the  connective  tissue  trabeculae  subdivide 
the  epithelium  into  spheroidal  groups  of  cells,  many  of  which  are  con- 
tinuous with  the  cell  columns  of  the  adjacent  zona  fasciculata.  The 
glomerulate  layer  is  relatively  thin  and  lies  close  beneath  the  capsule. 


550 


THE  DUCTLESS  GLANDS— ENDOCKIN  GLANDS 


The  stroma  of  the  zona  fasciculata  is  continued  inward  from  the 
glomerulosa,  but  is  so  drawn  out  as  to  form  elongated  areolae,  inclosing 


FIG.  478. — FROM  A  SECTION  THROUGH  THE  HUMAN  ADRENAL. 

a,  central  vein;  b,  capsule;  c,  zona  glomerulosa;  d,  zona  fasciculata;  e,  zona  reticu- 
laris;  /,  medulla;  g,  peri-adrenal  adipose  and  areolar  tissue.  Hematein  and  eosin. 
Photo.  X  45. 

cell  columns  of  considerable  length,  which  are  disposed  in  a  radial  man- 
ner. This  is  the  broadest  of  the  three  cortical  zones  and  is  interposed 
between  the  glomerulosa  and  reticularis. 


THE    SUPRARENAL    GLANDS 


551 


At  the  inner  border  of  the  zona  fasciculata  the  connective  tissue 
bundles  pass  insensibly  from  the  regular  columnar  arrangement  of  this 
layer  into  a  reticular  maze.  The  resulting  cell  groups  are  of  very  irregu- 
lar form  and  compose  the  innermost  cortical  layer,  the  zone  reticularis. 
This  layer  is  the 
thinnest  and  least 
distinct  of  the 
three  zones  of  the 
cortex.  It  can 
often  be  more  read- 
ily distinguished  by 
the  highly  pig- 
mented  condition 
of  its  cells,  than  by 
the  mere  form  of 
its  cell  columns. 
In  man  it  passes 
almost  insensibly 
into  the  medulla : 
in  many  animals — 
e.g.,  the  dog,  cat, 
and  pig — there  is.  a 
sharp  demarcation 
between  the  zona 
reticularis  and  the 
medulla,  produced 
by  a  thin  mem- 
branous layer  of 
connective  tissue 
which  apparently 
results  from  the 


FIG.  479. — PHOTOMICROGRAPH  OF  SUPRARENAL  GLAND  OF 
DOG.     Magnification   X  30. 

A,  loose  areolar  connective  tissue  of  outer  portion  of 
capsule  containing  two  large  (G)  and  several  small  gan- 


glia; c,  capsule  proper;  g,  zona  glomerulosa;  F,  zona  fascic- 
ulata; R,  zona  reticularis  of  cortex;  M,  medulla,  showing 
the  large  central  vein  (V). 


fusion   of  the  cen- 
tral   ends    of    the 
fibrous  bands  in  the 
cortical  stroma.     Such  a  membranous  septum  is  usually  wanting  in  the 
human  adrenal. 

The  connective  tissue  stroma  of  the  adrenal  consists  of  a  delicate 

vascular  network,  which  in  the  cortex  contains  very  few  if  any  elastic 

fibers.     Flint  (1900)  has  shown  that  this  connective  tissue  is,  in  large 

part,  at  least,  a  reticular  tissue.     The  capsule  consists  of  dense  bundles 

35 


552  THE  DUCTLESS  GLANDS— ENDOC^TN  GLANDS 

of  white  fibrous  tissue  among  which  are  many  elastic  fibers.    The  stroma 
of  the  medulla  is  also  richly  supplied  with  elastic  tissue. 

The  epithelium  of  the  zona  glomerulosais  arranged  in  spheroidal 
groups  or  in  hooked  or  slightly  coiled  columns  which  are  continuous 
with  the  straight  columns  of  the  fascicular  zone.  The  cells  of  the  zona 
glomerulosa  are  closely  packed  within  the  connective  tissue  meshes  and 


FIG.  480. — MORE  HIGHLY  MAGNIFIED  REGION  OF  THE  PRECEDING  SECTION,  TO 
SHOW  THE  CAPSULE  (C),  ZONA  GLOMERULOSA  (G),  AND  A  PORTION  OF  THE  ZONA 
FASCICULATA  (F). 

the  cell  outlines  are  very  indistinct.  Wherever  their  outlines  can  be 
readily  distinguished  the  cells  are  seen  to  be  of  columnar  shape  and  are 
arranged  in  slender  columns  whose  cells  are  often  grouped  about  an 
indistinct  central  lumen.  The  cytoplasm  of  the  cells  of  this  zone  is 
finely  granular  and  stains  readily  with  acid  dyes.  Occasional  minute  fat 
droplets  appear  in  the  innermost  cells  of  the  group,  but  these  are  never 
so  abundant  as  in  the  more  internal  portions  of  the  cortex.  The  nuclei 
in  this  zone  are  spheroidal  in  shape  and  rich  in  chromatin;  they  present 
frequent  mitoses  (Canalis,  1877),  but  these  are  more  abundant  in  early 
-life  than  in  the  adult. 

The  cells  of  the  zona  fasciculata  are  highly  characteristic.    They 


THE  SUPEARENAL  GLANDS  553 

are  arranged  in  long  straight  columns  which  extend  from  the  zona 
glomerulosa  inward  to  the  zona  reticularis.  The  cells  are  columnar  or 
polyhedral  in  shape ;  many  of  them  contain  minute  fatty  droplets  in  great 
abundance.  This  fat  is  readily  blackened  by  osmic  acid.  Arnold  (1902), 
by  extraction  with  ether,  obtained  crystals  of  palmatin  and  stearin  from 
the  suprarenal  gland.  Plecnik  (1902),  however,  considers  that  the 
adrenal  fat  differs  in  its  ultimate  chemical  properties  from  the  other  fat 
of  the  body.  Each  columnar  group  consists  of  cells  which  are,  as  a  rule, 
in  approximately  the  same  stage  of  fatty  metamorphosis,  and  the  cell 
columns  of  this  zone  may  be  divided  into  those  which  are  distinctly 
acidophil  and  those  which  are  distinctly  fatty,  though  between  these 
extremes  there  are  many  intermediate  stages. 

The  acidophil  cells  are  ovoid  or  polyhedral  elements  which  possess 
one  or  two  highly  chromatic  spheroidal  nuclei  and  a  finely  granular 
cytoplasm.  On  careful  examination  with  high  magnification,  extremely 
minute  fat  droplets  may  often  be  demonstrated  even  in  the  most  char- 
acteristic of  these  cells;  with  lower  magnification  these  are  frequently 
invisible. 

The  fatty  cells  possess  a  spheroidal  nucleus  which  is  usually  vesicular 
in  character;  occasionally  it  is  highly  chromatic.  Frequently  the  ap- 
parent chromatolysis  seems  to  progress  in  exact  ratio  to  the  accumulation 
of  fat;  those  cells  in  which  the  fatty  metamorphosis  is  more  advanced 
present  the  more  typically  vesicular  nucleus.  With  the  progress  of  the 
fatty  metamorphosis  the  cell  outlines  are  again  lost  and  the  granular 
acidophil  cytoplasm  gradually  replaced.  The  presence  of  fat  in  the  broad 
zona  fasciculata  is  partially  responsible  for  the  bright  yellow  color  of 
the  cortex  of  the  organ. 

The  cells  of  the  zona  reticularis  are  similar  to  those  of  the  zona 
fasciculata,  though  the  fatty  metamorphosis  is  le*ss  pronounced.  In  one 
particular,  however,  the  cells  of  this  layer  are  remarkable.  They  con- 
tain an  abundance  of  a  peculiar  brownish-yellow  pigment  which  occurs 
both  in  the  form  of  coarse  granules  and  as  a  diffuse  coloration  of  the 
cytoplasm.  The  spherical  nuclei,  highly  chromatic  or  only  slightly 
vesicular  in  character,  are  not  invaded  by  the  pigmentation.  The  vol- 
ume of  pigment  varies  greatly  in  different  individuals;  it  is  usually 
absent  in  young  persons,  but  is,  as  a  rule,  present  after  the  twentieth 
year  of  life  (Maass,  1889).  In  the  suprarenal  of  the  mouse  many  of 
these  cells  can  be  seen  in  process  of  amitotic  division. 

The  epithelial  cells  of  the  medulla  are  ovoid  elements  with  one 
or  two  spherical  nuclei,  which  in  many  cases  possess  a  vesicular  char- 


554  THE  DUCTLESS  GLANDS— ENDOCKIN  GLANDS 

acter;  in  other  cells  they  consist  of  a  dense,  almost  solid,  mass  of  chro- 
matin.  The  shape  of  the  cell  groups  in  the  medulla  varies  greatly; 
usually  they  form  small  spheroidal  masses  or  short  columns.  The  cells 
are  frequently  arranged  in  a  more  or  less  tubular  form  but  without 
a  distinct  lumen.  Frequently  they  surround  a  minute  capillary  vessel. 
The  medullary  cells  presumably  pour  their  secretion  into  the  blood- 
vessels, Avhose  broad  sinusoidal  capillaries  permeate  the  delicate  connec- 
tive tissue  bands  which  inclose  the  cell  groups.  Felicine  (Arch.  f.  mikr. 
Anat.,  1904)  claims  to  have  demonstrated  the  presence  of  minute  intra- 
and  intercellular  secretory  canaliculi  which  open  directly  or  indirectly 
through  broader  lacunae,  into  the  blood-vessels. 

The  cell  groups  of  the  medulla,  like  those  of  the  cortex,  are  divisible 
into  the  acidophil  and  the  fatty  types;  the  former  are  the  more  abun- 
dant, but  the  fatty  metamorphosis  is  scarcely  ever  so  advanced  as  in  the 
cortex.  There  is,  however,  great  variation  in  the  size  of  the  medullary 
cells.  The  larger  ovoid  elements  form  the  typical  groups;  between 
these  groups  are  narrow  cell  columns  consisting  of  much  smaller  and 
less  highly  acidophil  cells,  which  are  arranged  in  slender  columns  and 
scattered  irregular  masses. 

The  striking  feature  of  the  medullary  cells  is  their  granular  content. 
These  chromaffin  granules  have  a  special  affinity  for  chromic  acid  and 
its  salts,  and  stain  a  light  brown  or  yellow.  "Their  staining  capacity  in 
chromium  solutions  is  due  to  the  presence  of  adrenalin  (Kingsbury, 
Anat.  Bee.,  5,  1,  1911).  The  granules  are  very  readily  soluble  in  acids. 

In  the  vicinity  of  the  central  veins,  small  nerve  trunks  are  found, 
and  occasional  minute  ganglia  or  isolated  nerve  cells  occur  along  their 
course.  These  are  not  to  be  confused  with  the  large  ovoid  epithelial  cells 
of  the  medulla. 

Blood  Supply. — The  arteries  which  supply  the  suprarenal  glands 
form  a  plexus  of  vessels  in  the  capsule  of  the  organ  and  in  the  neighbor- 
ing connective  tissue.  Some  of  the  smaller  branches  of  this  plexus,  the 
capsular  arteries,  supply  the  capsule  itself,  others  enter  the  organ  and 
are  distributed  to  the  cortex  and  to  the  medulla.  The  blood  supplied 
to  the  capsular  arteries,  after  traversing  the  capillaries,  enters  small 
venules  which  are  tributary  to  the  lumbar  and  phrenic  veins.  The  course 
of  the  cortical  and  medullary  vessels  has  been  exhaustively  studied  by 
Flint  (Proc.  Bost.  Soc.  of  Nat.  Hist.,  1900). 

The  cortical  arteries  enter  the  zona  glomerulosa  where  they  abruptly 
break  up  to  form  a  capillary  plexus  which  occupies  the  connective  tissue 
between  the  cell  columns.  Capillary  vessels  are  continued  from  this 


THE  SUPRARENAL  GLANDS  555 

plexus  through  tho  intercellular  reticulum  of  the  zona  fasciculata,  where 
they  arc  in  intimate  relation  with  the  epithelial  cells,  and  reach  the  zona 
reticularis.  Here  the  capillaries  are  collected  into  thin-walled  venules 
or  sinusoids.  These  vessels,  after  sonic  anastomoses,  form  venous  steins 
\\hich  arc  continued,  without  further  anastomosis,  throughwfrhe  medulla 
to  the  central  \cins.  The  venules  of  the  cortex  possess  no  walls  other 
than  their  endothelium. 

The  medullary  arteries  are  also  derived  from  the  capsular  plexus. 
They  penetrate  the  cortex,  and  at  the  border  of  the  medulla  abruptly 


FIG.  481. — RECONSTRUCTION  OP  A  DOG'S  ADRENAL. 
a,  arteries;  v,  vein.     X  25.     (After  Flint.) 

terminate  in  a  plexus  of  capillary  vessels  which  lie  in  the  connective 
tissue  stroma  and  come  into  intimate  relation  with  the  medullary  cells. 
These  vessels  possess  extremely  thin  walls,  their  endothelium  often  being 
in  direct  contact  with  the  adjacent  epithelium,  whose  cells  frequently  im- 
pinge upon  the  lumen  of  the  capillary  vessel  (see  Fig.  481).  The  capil- 
lary plexus  pervades  the  entire  medulla,  its  vessels  being  here  and  there 
collected  into  small  veuules  which  unite  to  form  the  central  veins. 
These  form  two,  or  sometimes  four,  main  stems  (Flint)  which  make 
their  exit  at  the  hilum  and  enter  the  lumbar  or  renal  vein,  or,  on  the 
right  side,  enter  the  inferior  vena  cava. 

All  of  the  efferent  veins  of  the  adrenal  are  characterized  by  a  peculiar 
distribution  of  their  smooth  muscle  fibers,  which  occur  in  considerable 
abundance,  but  are  nearly  all  disposed  in  the  axis  of  the  vessel;  tho 


556 


THE  DUCTLESS  GLANDS— ENDOCBIN  GLANDS 


form  rich  plex- 


circular  muscle  fibers  are  confined  to  a  very  thin  coat  beneath  the  endo- 
thelium,  or  are  often  entirely  absent.  Frequently,  and  especially  in  the 
central  veins  of  the  adrenal,  the  coarse  bundles  of  longitudinal  muscle 
fibers  project  into  the  lumen  of  the  vessel  in  a  somewhat  rugose  manner. 
Whenever  two  veins  unite  to  form  a  larger  vessel,  and  at  the  junction  of 
a  central  vein  with  any  of  its  branches,  these  protuberant  muscular 
bundles  are  especially  prominent.  Moreover,  Ferguson  (Amer.  Jour. 
Anat.,  5,  1,  1905)  describes  anomalous  vessels  of  a  venous  nature  which 

arise  in  the  medulla,  penetrate  the 
cortex,  and  enter  the  venous  plexus 
of  the  capsule;  and  in  these  in- 

'•^r-  .  ^^  /*^€f*2r  stances  the  same  peculiar  distribu- 

w  '^^  tion  of  the  muscle  has  been  observed 

'   *n  ^ne  ve*ns  °^  the  caPsular  plexus. 
Lymphatics.—  The      lymphatics 
°^  the  suprarenal  gland,  according 
to  Stilling  (I88 
uses  *n  the  zona 

the  medulla;  elsewhere  they  are  less 
abundant.  They  follow  the  course 
of  the  blood-vessels  and  are  espe- 
cially well  developed  in  the  vicinity 
of  the  central  veins. 

Nerves.—  The  adrenal  is  well 
supplied  with  small  sympathetic 
nerve  trunks  from  the  solar  plexus. 
They  form  a  plexus  in  the  capsule 
from  which  branches  are  distributed 
to  the  cortex  and  to  the  medulla. 
In  the  cortex  they  invest  the  blood- 
vessels with  a  delicate  plexus,  but  have  not  been  found  within  the  epithe- 
lial cell  columns.  In  the  medulla  they  are  also  distributed  to  the  blood- 
vessels and  are  supplied  with  occasional  small  ganglia.  Passing  from 
the  plexus  of  sympathetic  nerve  fibers  which  invests  the  groups  of  medul- 
lary epithelium,  Dogiel  (1894)  demonstrated  delicate  fibrils,  supplied 
with  minute  varicosities,  which  penetrate  between  the  epithelial  cells  and 
terminate  in  a  manner  very  similar  to  that  which  is  characteristic  of  the 
epithelial  parenchyma  of  other  secreting  glands. 

Accessory  Suprarenals.—  These  include   bodies  of  three  types  of 
structure:  (1)  bodies  consisting  exclusively  of  cortical  substance;  (2) 


FIG.  482. — SECTION'  OF  PART  OF  AN  AC- 
CESSORY SUPRARENAL  (CHROMO- 
PHIL  BODY),  NEW-BORN  CHILD. 

chr,   a  chromophil    cell.      (Schafer, 
"  Quain's  Anatomy.") 


THE  THYROID  GLAND  557 

bodies  composed  exclusively  of  medullary  substance  and  indistinguish- 
able from  paraganglia;  and  (3)  the  true  accessory  (supernumerary) 
suprarenals  consisting  of  both  cortex  and  medulla.  These  bodies  are 
widely  distributed  in  the  vicinity  of  the  suprarenal,  sometimes  embedded 
within  its  substance,  sometimes  in  the  kidney  or  even  in  the  liver. 
They  vary  in  size  from  microscopic  bodies  to  such  with  a  diameter  of  a 
centimeter  or  more.  They  are  frequently  found  also  in  connection  with 
the  genital  system,  a  rather  large  representative  being  almost  invariably 
present  in  the  space  between  the  testis  and  the  epididymis,  and  in  the 
broad  ligament  of  the  female  close  to  the  ovary,  where  it  is  known  as 
Marcliand's  gland  or  Marchand's  adrenal. 


II.     THE    THYROID    GLAND 

The  THYROID  consists  of  a  mass  of  glandular  tubules  or  follicles, 
supported  by  a  connective  tissue  stroma  and  supplied  with  a  thin  but 
dense  fibrous  capsule  which  closely  invests  the  surface  of  each  of  its 
lobes. 

The  Connective  Tissue  Framework.--The  capsule  of  the  thyroid 
consists  of  dense  fibro-elastic  tissue,  from  which  trabeculae,  containing 
the  larger  blood-vessels,  pass  inward  and  produce  an  indistinct  lobular 
subdivision.  A  network  of  delicate  fibers,  among  which  are  very  few 
if  any  elastic  fibers,  passes  from  the  trabeculaB  and  invests  the  glandular 
follicles,  forming  a  delicate  basement  membrane  for  their  epithelium. 
Flint  (1903)  has  shown  that  much  of  this  interfollicular  connective  tis- 
sue is  of  the  reticular  variety.  In  it  are  contained  the  smaller  blood- 
vessels and  lymphatics.  It  also  contains  a  few  lymphocytes,,  which  are 
scattered  about  in  a  diffuse  manner. 

The  FOLLICLES  of  the  thyroid  are  ovoid  saccules  or  short  branched  tu- 
bules with  frequent  diverticula  (Streiff,  Arch.  mikr.  Anat.,  1897).  They 
vary  greatly  in  diameter  and  in  the  caliber  of  their  lumen.  Many  of 
them  present  scarcely  any  lumen;  others,  by  their  extreme  size  (100  to 
200  >"),  simulate  small  cysts.  All  follicles  which  possess  any  consider- 
able lumen  contain  a  peculiar  acidophil  substance,  known  as  colloid, 
which  is  apparently  formed  by  the  secretory  activity  of  the  glandular 
epithelium  lining  the  follicles. 

Colloid  is  a  homogeneous  or  very  finely  granular  substance  which 
stains  readily  with  eosin,  taking  a  very  bright  tint  closely  resembling 
that  acquired  by  the  hemoglobin  of  the  red  blood  cells.  Frequently, 


558 


THE  DUCTLESS  GLANDS— ENDOCKIN  GLANDS 


and  especially  in  specimens  which  have  been  fixed  and  hardened  in  alco- 
hol, it  presents  a  vacuolated  appearance.  As  a  rule  the  lumen  of  the 
follicle  is  not  completely  filled  with  the  colloid  mass,  which  is  then 
adherent  to  the  surface  of  the  lining  epithelium  by  delicate  thread-like 


FIG.  483. — FROM  A  SECTION  OF  THE  HUMAN  THYROID  GLAND. 

a,  thyroid  follicles  in  transaction;    b,  tangential  section  of  the  follicular  wall. 
Hematein  and  eosin.     Photo.     X  110. 

processes;  the  colloid  thus  acquires  a  deceptive  appearance  of  extreme 
contraction,  as  if  its  surface,  except  for  occasional  delicate  strands,  had 
been  drawn  away  from  the  epithelium. 

Occasionally  a  single  large  vacuole,  often  containing  basophil  gran- 
ules or  crystalloid  particles,  occupies  the  center  of  the  colloid  mass  in 
the  larger  follicles;  at  other  times  the  colloid  material  appears  to  be 


THE   THYEOID  GLAND  559 

broken  into  minute  spherules.  In  general,  the  ratio  of  colloid  content 
within  the  follicle,  roughly  stated,  is  in  proportion  to  the  age  of  the  in- 
dividual. The  follicles  at  the  periphery  of  the  lobes  of  the  gland  are 
less  fully  distended  than,  those  in  the  interior. 

Embedded  in  the  colloid  mass  within  the  follicle,  even  in  the  appar- 
ently normal  thyroid,  red  blood  corpuscles  and  desquamated  follicular 
epithelium  are  frequently  found,  but  never  in  large  quantity.  Leuko- 
cytes are  of  less  frequent  occurrence  and  are  more  rarely  found  in  the 
human  thyroid  than  in  that  of  the  lower  mammals. 

The  FOLLICULAR  EPITHELIUM  is  typically  cuboidal  in  shape;  in 
young  individuals  it  is  somewhat  taller  than  broad.  In  those  follicles 
which  are  distended  with  colloid  secretion  the  epithelium  is  relatively 
short ;  in  those  which  are  empty  it  is  taller.  Each  cell  contains  a  single 
spheroidal  nucleus  which  lies  in  the  center  of  the  cell,  or  somewhat 
toward  its  basal  extremity.  This  orderly  disposition  causes  the  nuclei, 
when  seen  in  sections  of  the  follicle,  to  appear  as  a  continuous  row  in 
the  wall  of  the  alveolus,  a  disposition  which  is  noticeable  for  its  ex- 
ceptional regularity. 

The  cytoplasm  of  the  epithelium  is  finely  granular  and  decidedly 
acidophilic.  It  usually  contains  some  coarse  granules  and  very  small 
fatty  droplets,  which  generally  occupy  the  extremities  of  the  cells.  Mi- 
nute spheroidal  granules  which  give  the  color  reactions  of  colloid  are 
also  found  in  the  cytoplasm  of  the  epithelial  cells.  Hiirthle  (Arch.  f.  d. 
ges.  Physiol.,  1894),  by  staining  with  the  Biondi-Ehrlich  mixture,  suc- 
ceeded in  differentiating  two  types  of  cell,  one  lightly  staining,  the 
'chief  cells,'  the  other  a  darker  colloid-containing  type  which  he  designated 
as  'colloid  cells/  These  variations  probably  only  represent  different 
stages  of  secretion  in  the  same  epithelial  cell  type.  Minute  intercellular 
canaliculi  occur  at  the  angles  between  adjacent  cells. 

In  the  thyroid  of  the  opossum  Bensley  (Anat.  Rec.,  8,  9,  1914)  also 
describes  two  types  of  cells,  namely,  the  usual  epithelial  cells  and  ovoid 
cells.  The  latter  hold  a  parietal  position  in  the  follicle;  they  are  filled 
with  fine  eosinophilic  granules  which  give  to  these  cells  a  character  strik- 
ingly similar  to  that  of  the  acidophil  cells  of  the  anterior  lobe  of  the  hypo- 
physis cerebri.  He  describes  also  large  needle-shaped  crystalloid  bodies  in 
the  epithelial  cells  similar  to  those  in  the  interstitial  and  Sertoli  cells  of 
the  testis. 

The  epithelium  rests  upon  a  very  delicate  reticular  basement  mem- 
brane and  is  in  close  relation  with  the  capillaries  and  lymphatic  vessels 


560 


THE  DUCTLESS  GLANDS— ENDOCRIN  GLANDS 


of  the  interfollicular  stroma.  Colloid  material,  similar  to  that  within  the 
follicles,  has  been  repeatedly  found  within  the  lymphatic  vessels  (Baber, 
Langendorf,  Hiirthle)  and  may  be  readily  demonstrated  in  most  sections 

,  of   the  thyroid.     Un- 

doubtedly this  does 
not,  however,  repre- 
sent the  entire  'inter- 
nal secretion'  of  the 
gland. 

Blood  Supply.  — 
The   arteries   form    a 
rich    plexus    in    and 
about  the  capsule  of 
the    thyroid,    from 
y  which     numerous 
branches  penetrate  the 
organ,    lying    in    the 
connective  tissue  trab- 
eculse  between  the  lo- 
bules;   they    are    dis- 
tributed  to  all  parts 
of   the   gland.      They 
supply  a  rich  capillary 
FIG.  484.— DIAGRAM  OF  PHARYNX  OP  HUMAN  EMBRYO,      plexus  in  the  walls  of 
SHOWING  THE  ORIGINS  OF  THE  ANLAGES  OF  THE     the     follicles.       The 
THYMUS,  THYROID  AND  PARATHYROIDS  (EPITHELIAL 
BODIES). 

Thy1,  earliest  position  of  thyroid  anlage;  Thy2,  sec- 
ondary position  of  thyroid  anlage;  Tgd,  thyroglossal 
duct;  Fc,  foramen  cecum;  LThy,  lateral  thyroid  an- 
lages;  Ptky,  parathyroid  bodies;  pb,  postbranchial 
body;  T,  tonsil;  /,  II,  III,  IV,  V,  pharyngeal  pouches; 
a,  6,  first  and  second  branchial  grooves  ('gill  clefts'); 
1,  2,  3,  first,  second  and  third  aortic  arches  in  the 
cores  of  the  branchial  arches.  The  complete  wall  of 
the  pharynx  is  only  shown  at  the  right,  above.  (Adapt- 
ed from  Kohn.) 


veins  retrace  the 
course  of  the  arteries. 
The  walls  of  the 
smaller  venules  consist 
only  of  endothelium, 
with  a  very  thin  coat 
of  fibro-elastic  connec- 
tive tissue. 

Lymphatics. — The 


thyroid  is  very  abun- 
dantly supplied  with  lymphatic  vessels.  These  form  a  plexus  of 
very  broad  lacunar  capillaries  in  the  interfollicular  connective  tissue, 
where  they  stand  in  intimate  relation  with  the  follicular  epithelium. 
From  this  plexus  vessels  pass  to  the  interlobular  connective  tissue,  in 
which  they  form  a  second  plexus,  whence  lymphatic  vessels  pass  out  of 


THE  THYEOID  GLAND  561 

the  thyroid  in  company  with  the  blood-vessels  and  enter  the  deep  cer- 
vical lymph  nodes. 

Nerves. — The  nerves  of  the  thyroid  are  derived  from  the  sympa- 
thetic system  and  are  mostly  non-medullated.  They  accompany  the  ar- 
teries and  form  a  delicate  terminal  plexus  in  the  walls  of  the  follicles. 
The  finer  fibrils  of  this  plexus  end  in  contact  with  the  epithelium. 
Berkeley  (1895)  describes  also  occasional  fibrils  which  apparently  pene- 
trated between  the  epithelial  cells. 

Development. — The  thyroid  develops  from  three  anlages,  a  median  and 
a  pair  of  lateral  outgrowths  from  the  primitive  pharynx.  The  median 
anlage  sprouts  from  the  floor  of  the  pharynx  at  the  level  of  the  first 
pharyngeal  pouches.  Its  site  of  origin  is  marked  in  the  adult  by  the 
foramen  cecum  of  the  tongue.  It  forms  the  isthmus  and  pyramidal  lobe 
(process)  of  the  definitive  thyroid.  The  lateral  anlages  grow  down  from 
the  ventral  border  of  the  fourth  pharyngeal  pouches;  they  form  the  lateral 
lobes  of  the  gland.  The  pyramidal  lobe  represents  the  remnant  of  the 
embryonic  thyroglossal  duct;  it  varies  greatly  in  length  in  different  indi- 
viduals; it  may  even  retain  a  partial  lumen  which  may  be  filled  with  col- 
loid, but  it  does  not  open  upon  the  surface.  The  primary  anlages  consist 
of  solid  cords  of  cells;  the  cords  subsequently  acquire  a  lumen,  and  become 
broken  up  into  lobules  and  follicles  through  the  invasion  of  connective 
tissue.  According  to  Grosser  the  definitive  thyroid  arises  exclusively  from 
the  median  anlage. 

Function. — Bemoval  of  the  thyroid  is  followed  by  serious  symptoms 
and  frequently  fatal  results,  particularly  in  the  case  of  the  carnivora.  Its 
internal  secretion  is  apparently  necessary  for  normal  metabolism  and  devel- 
opment. It  governs  the  conditions  favoring  tissue  oxidation  (Crile).  The 
essential  secretion  is  probably  something  apart  from  the  colloid  and  iodin 
content  of  the  gland.  According  to  Crile  the  active  constituent,  thyroiodin, 
is  iodin  in  a  special  proteid  combination.  The  belief  that  the  thyroid  has 
also  an  antitoxic  role  is  based  chiefly  on  the  observation  that  thyroidec- 
tomized  animals  are  extremely  liable  to  certain  infections.  Gudernatsch's 
experiments  with  frog  tadpoles  show  that  a  thyroid  diet  accelerates  differ- 
entiation but  inhibits  growth:  the  tadpoles  metamorphosed  prematurely 
into  diminutive  frogs — a  result  the  opposite  of  that  obtained  when  thymus 
is  fed.  An  enlarged  thyroid  is  commonly  known  as  a  'goitre.'  Enlargement 
may  be  due  to  increase  in  the  amount  of  the  connective  tissue  or  of  the 
colloid  parenchyma ;  one  results  in  atrophy  of  the  parenchyma  and  a  condi- 
tion of  byposecretion,  associated  with  myxedema  and  in  extreme  cases  with 
cretinism — an  apparently  hereditary  defect;  and  the  other  in  hypersecre- 
tion,  associated  with  exophthalmic  goitre  (Grave's  disease).  In  man  and 
animals  the  thyroid  shows  a  seasonal  enlargement  related  to  the  sexual  cycle. 


562 


THE  DUCTLESS  GLANDS— ENDOCBIN  GLANDS 


ACCESSORY  OR  ABERRANT  THYROIDS 

These  bodies,  first  described  by  Zuckerkandl  (1879),  are  widely  dis- 
tributed through  the  connective  tissue  of  the  cervical  region.  They 
are  most  frequently  found  in  the  course  of  the  embryonic  thyroglossal 


FIG.  485. — FROM  THE  BORDER  OF  A  MASS  OK  ABERRANT  THYROID  TISSUE  OF  MAN, 
OCCURRING  IN  THE  REGION  OF  THE  PARATHYROID  GLANDS. 

Hematein  and  eosin.     Photo.     X  204. 


duct  and  in  the  immediate  vicinity  of  the  lateral  lobes  of  the  thyroid. 
They  present  the  appearance  of  embryonal  remnants  of  thyroid  tissue, 
but  are  found  in  nearly  all  individuals. 

The   colloid   follicles   of  the   aberrant   thyroids   are    usually   small, 
though,  in  the  larger  specimens  of  these  bodies,  they  may  attain  as  great 


THE  PAEATHYROID  GLANDS  563 

a  size  as  those  of  the  thyroid  itself.  The  cell  columns  without  colloid 
are  more  numerous  than  in  the  thyroid  gland,  giving  to  the  aberrant 
bodies  a  decidedly  cellular  appearance.  Each  aberrant  mass  is  usually 
inclosed  by  a  very  thin  connective  tissue  capsule  which  sends  delicate 
processes  between  the  cell  groups.  The  epithelial  cells  retain  all  the 
characteristics  of  those  of  the  thyroid  gland,  and  can  be  readily  distin- 
guished from  the  epithelium  of  the  parathyroid  glands  with  which  the 
accessory  thyroid  bodies  have  been  frequently  confused.  They  are  also 
much  less  vascular  than  the  parathyroids. 


III.    THE  PARATHYROID   GLANDS 

The  PARATHYROIDS,  or  epithelial  bodies,  are  small  glandular  bodies 
of  irregular  distribution,  usually  found  in  relation  with  the  posterior 
margin  of  the  lateral  lobes  of  the  thyroid  gland.  They  arise  as  buds  from 
the  dorsal  pockets  of  the  third  and  fourth  pharyngeal  pouches.  Typi- 
cally four  parathyroids  are  present,  the  superior  pair  situated  near  the 
lateral,  the  inferior  near  the  median  margin  of  the  lateral  lobes  of  the 
thyroid.  The  inferior  pair  in  the  adult  develops  from  the  anterior  pair 
of  anlages,  and  frequently  becomes  embedded  in  the  thyroid  tissue.  They 
may  occur  also  in  relation  with  the  tracheal  or  laryngeal  wall  and  may 
be  found  as  high  as  the  hyoid  bone  or  as  low  as  the  border  of  the  thymus. 
They  also  vary  greatly  in  size  and  shape,  but  usually  are  of  ovoid  form 
and  about  three  to  five  millimeters  in  diameter. 

Each  parathyroid  is  invested  by  a  thin  capsule  of  dense  connective 
tissue  and  consists  of  a  mass  of  epithelial  cells  supported  by  a  delicate 
fibrous  reticulum.  The  epithelial  cells  are  of  two  chief  types,  desig- 
nated by  Welsh  (Jour.  Anat.  and  Physiol.,  1898)  as  the  'principal*  and 
the  'oxyphil'  or  acidophil  cells-. 

The  principal  cells  are  the  more  abundant.  They  are  ovoid  or 
spheroidal  elements,  with  a  clear  vesicular  cytoplasm,  a  distinct  cell 
membrane,  and  a  large  spherical  nucleus,  whose  chromatin  is  irregularly 
distributed  and  often  gives  the  nucleus  a  somewhat  vesicular  character. 

The  acidophil  cells  are  of  similar  shape  but  are  provided  with  a 
small  spherical  nucleus,  which  is  very  rich  in  chromatin,  and  a  granular 
acidophilic  cytoplasm.  The  acidophil  are  less  numerous  than  the 
principal  cells. 

The  distribution  of  the  epithelial  cells  is  subject  to  considerable  vari- 
ation. Most  frequently  they  form  an  almost  solid  epithelial  mass,  in 


564. 


THE  DUCTLESS  GLANDS— ENDOCRIN  GLANDS 


which  capillary  vessels  are  here  and  there  found,  the  larger  blood-vessels 
occupying  the  coarser  bands  of  the  fibrous  stroma.  In  such  glands  the 
two  cell  varieties  are  either  intermingled  irregularly,  or  the  acidophil 
cells  may  occur  in  scattered  groups  which  are  interspersed  among  the 
more  numerous  principal  cells. 

In  certain  instances  the  epithelial  cells  are  arranged  in  small  alveo- 


FIG.  486. — HUMAN  PARATHYROID  TISSUE,  MODERATELY  MAGNIFIED. 

Several  blood-vessels  are  included.    Capillary  vessels  can  scarcely  be  recognized 
with  this  magnification.     Hematein  and  eosin.     Photo.     X  300. 

lar  groups  which  are  surrounded  by  a  network  of  capillary  vessels.  This 
arrangement  appears  to  be  more  frequent  in  young  individuals.  The 
cell  groups  in  this  type  of  gland  frequently  form  branching  columns. 

Occasionally,  epithelial  cells  surround  a  central  lumen,  in  which  are 
small  masses  of  an  acidophil  substance  which  resembles  colloid  in  its 
reactions.  This  colloidal  material  is  less  abundant  in  the  human  para- 


THE  THYMUS  565 

thyroid  than  in  that  of  the  lower  mammals.  Likewise  the  cystic  ducts, 
lined  by  columnar  or  ciliated  columnar  epithelium,  which  have  been  de- 
scribed by  Kohn  (1897),  though  of  frequent  occurrence  in  the  lower 
mammals  are  rarely,  if  ever,  found  in  the  human  parathyroid. 

The  parathyroids  and  the  thyroid  are  frequently  in  anatomical  con- 
tinuity; this  area  is  characterized  by  transitional  histologic  conditions. 
Moreover,  af^er  thyroidectomy  the  parathyroids  may  alter  their  structure 
so  as  to  resemble  very  closely  thyroid  tissue.  The  parathyroids  are  gen- 
erally regarded  as  having  a  function  absolutely  essential  to  life.  How- 
ever, the  experimental  evidence  touching  this  point  is  conflicting.  But 
in  certain  forms,  e.g.,  cat  and  dog,  extirpation  produces  tetany  which 
results  in  death.  Vincent  interprets  the  experimental  data  as  indi- 
cating that  the  thyroid  and  the  parathyroids  constitute  parts  of  the 
same  apparatus,  to  which  the  pars  intermedia  of  the  hypophysis  cerebri 
may  have  to  be  added-  as  a  third  constituent. 

The  connective  tissue  of  the  gland  is  of  variable  quantity.  It  forms 
a  thin  but  dense  capsule;  occasionally  trabeculas  extend  inward  and 
partially  outline  indistinct  lobules.  In  many  instances  a  hilum  trans- 
mits the  larger  blood-vessels  by  means  of  vascular  trabecula?  which 
radiate  to  all  portions  of  the  organ.  A  delicate  fibrous  or  reticular 
stroma  invests  the  individual  cells,  or  the  cell  groups,  when  these  are 
present.  Occasionally  the  cells  are  so  closely  packed  that  the  stroma  is 
scarcely  demonstrable. 

The  blood  supply  of  the  parathyroid  is  exceedingly  rich.  Ar- 
teries enter  from  the  capsule,  or  at  the  hilum,  and  rapidly  break  up 
into  a  plexus  of  broad  capillary  or  sinusoidal  vessels  which  follow  the 
fibrous  bands  of  the  stroma  and  are  in  intimate  relation  with  the  epi- 
thelium. They  are  collected  into  thin-walled  venules  which  retrace 
the  course  of  the  arteries. 


IV.     THE    THYMUS 

The  THYMUS  was  formerly  regarded  as  an  organ  of  fetal  and  in- 
fantile life,  and  was  believed  to  attain  its  maximum  development  during 
the  second  year  of  childhood.  After  this  time  it  was  thought  to  be- 
come gradually  replaced  l>y  nilipose  tissue,  its  retrograde  metamorphosis 
reaching  completion  at  about  the  age  of  puberty.  However,  Waldeyer 
(1890)  showed  that  the  thymus  may  persist  even  in  advanced  age  as 
a  body  of  considerable  size,  and  apparently  functional.  The  more  recent 


566  THE  DUCTLESS  GLANDS— ENDOCKIN  GLANDS 

studies  of  Hammar  (1906)  and  others  indicate  that  the  thymus  nor- 
mally continues  its  development  until  about  the  time  of  puberty. 
Subsequently  it  loses  slowly  in  weight,  but  a  true  atrophy  of  the 
parenchyma  with  cessation  of  function,  does  apparently  not  occur  until 
about  the  age  of  fifty. 

It  is  still  uncertain  whether  the  thymus  should  be  classified  with 


FIG.  487. — A  SECTION  THROUGH  SEVERAL  LOBULES  OF  THE  THYMTJS  OF  AN  INFANT. 

a,  loose  fibrous  septum  between  the  lobules;  b,  cortex,  and  c,  medulla  of  the  lobule; 
d,  blood-vessels  in  the  connective  tissue.    Hematein  and  eosin.    Photo.     X  60. 

lymphoid  organs  or  with  endocrin  glands.  Eecent  investigations  in- 
creasingly indicate  that  it  is  essentially  of  lymphoid  character  but  func- 
tions, in  part  at  least,  as  an  organ  of  internal  secretion,  related  to 
normal  growth  and  sexual  development. 

At  its  maximum  the  thymus  forms  a  large  lymphoid  mass,  embedded 
in  areolar  connective  tissue,  the  trabeculae  of  which  divide  the  organ 
into  several  lobes  and  innumerable  minute  lobules.  Each  lobule  is 
surrounded  by  a  thin  fibrous  capsule,  by  which  it  is  loosely  united  to  its 
neighbors. 

The  lobule  consists  of  a  mass  of  lymphoid  tissue,  which  is  dense  at 
the  periphery  but  looser  in  the  central  portion.  It  is  thus  divisible 
into  a  dense  cortex  and  a  loose  medulla,  both  composed  essentially  of 
lymphoid  tissue,  but  between  which,  because  of  the  difference  in  density, 
there  is  a  sharp  line  of  demarcation.  Frequently,  at  some  point  on 


THE  THYMUS 


567 


its  circumference,  the  medulla  reaches  the  surface  of  the  lobule,  and 
at  such  locations  a  narrow  column  of  medullary  lymphoid  tissue  connects 
it  with  the  adjoining  lobule. 

A  close-meshed  reticulum,  within  the  narrow  meshes  of  which  are 
closely  packed  lymphoid  cells,  composes  the  lymphoid  tissue  of  the  lobule. 
That  of  the  cortex  and  the  medulla  is  alike,  except  for  the  fact  that 
the  meshes  of  the  reticulum  in  the  cortex  are  much  more  crowded 
with  'lymphocytes'  than  are  those  of  the  medulla.  The  medulla  of 
each  lobule  is  also  charac- 

^_   .       , -     /-^V.^ 

terized  by  the  presence  of 
several  groups  of  concen- 
trically arranged  epitheli- 
oid  cells,  the  tJiymic  cor- 
puscles (concentric  corpus- 
cles of  Hassall). 

Each  thymic  corpuscle 
consists  of  a  large  central 
cell  or  group  of  cells,  which 
is  surrounded  by  two  to  five 
layers  of  concentrically  ar- 
ranged flat  epithelioid  cells. 

These  groups  or  cell  nests  FJG  48g  _A  THYMIC  CoRPUSCLE  FROM  THE 
are  strongly  acidophil  in  THYMUS  OF  AN  INFANT. 

their    staining   reactions,  Hematein  and  eosin.     X  665. 

and  therefore  stand  out  in 

marked  contrast  to  the  basophilic  nuclei  of  the  surrounding  lymphoid 
tissue.  A  substance  simulating  the  colloid  of  the  thyroid  may  be  present 
among  the  cells.  Since  no  similar  structure  occurs  elsewhere  in  the  body, 
the  concentric  corpuscles  are  absolutely  characteristic  of  the  thymus 
lobule. 

The  nature  of  the  thymic  corpuscles  is  not  satisfactorily  understood. 
According  to  one  hypothesis  they  represent  blood-vessels  whose  lumen 
has  been  obliterated  by  proliferation  of  its  endothelial  cells.  Another 
theory  regards  them  as  remains  of  the  epithelial  columns  from  which 
the  organ  arose  in  the  embryo.  They  are  also  interpreted  as  masses 
of  hypertrophied  cells  of  the  reticulum. 

The   tij/H'x  of  lymphoid  corpuxrlc  which  are  found  in  the  thymus 

;uv   similar    to    those   of    Hie    lymph    nodes,   though    polymorphonuclcnr 

leukocytes  are  rather  more  frequent  here,  and  giant  cells,  mononuclear 

or  multinuclear  in  form,  may  be  readily  found  in  the  medulla  of  this 

36 


568  THE  DUCTLESS  GLANDS— ENDOCRIN  GLANDS 

organ.  Pappenheimer  regards  the  specific  cells  of  the  thymus  as  epi- 
thelial in  character,  simulating,  but  not  identical  with,  lymphocytes. 

Blood  Supply. — The  larger  arteries  of  the  thymus  are  distributed 
within  the  interlobular  connective  tissue.  They  supply  branches  to  the 
lobule  which  penetrate  to  the  medulla,  where  they  form  a  plexus  of 
sinusoidal  capillaries  with  elongated  meshes,  and  also  distribute  radi- 
ating capillaries  to  the  cortical  portion  of  the  lobule.  These  sinusoidal 
vessels  are  highly  characteristic  of  the  medulla  of  the  thymus  lobule. 
They  unite  to  form  venous  radicals  of  considerable  caliber,  which  leave 
the  lobule  to  join  the  interlobular  veins  in  the  loose  connective  tissue 
between  the  lobules. 

Lymph  vessels  are  of  frequent  occurrence  in  the  iuterlobular  con- 
nective tissue,  and  their  branches  occasionally  penetrate  to  the  medulla 
of  the  lobule,  but  there  is  nothing  corresponding  to  the  lymph  sinuses 
of  lymph  nodes.  Small  non-medullated  nerve  trunks  are  also  found 
in  the  interlobular  connective  tissue,  but  seem  to  be  chiefly  distributed 
to  the  walls  of  the  larger  blood-vessels. 

Development  and  Function  of  the  Thymus. — The  thymus  arises  as 

a  pair  of  tubular  outgrowths  from  the  ventral  aspect  of  the  third  pharyn- 
geal  pouch,  which  subsequently  become  solid  and  fuse  to  form  a  median, 
flat,  bi-lobed  organ  lying  in  the  root  of  the  neck  and  the  upper  portion  of 
the  thorax.  According  to  certain  investigators  (Stohr,  et  al.)  the  lymphoid 
cells  of  the  definitive  organ  are  derived  from  the  entodermal  cells  of  the 
initial  anlages.  The  recent  work  of  Maximow  (Arch.  mikr.  Anat,  74,  3, 
1909),  however,  seems  to  demonstrate  that  these  cells  are  true  lymphocytes 
and  that  they  have  their  origin  in  the  surrounding  mesenchyme,  from  the 
cells  of  which  they  differentiate,  and  from  which  location  they  migrate  into 
the  thymus  anlages — a  conclusion  confirmed  by  the  still  more  recent  work 
of  Badertscher  (Amer.  Jour.  Anat.,  17,  4,  1915).  The  original  lymphocytes 
are  said  to  be  of  the  large  variety ;  these  give  rise  through  proliferation  with- 
in the  thymus  to  the  smaller  types.  Among  the  invading  leukocytes  are  also 
a  small  number  of  polymorphs.  The  original  epithelial  anlages  continue  to 
grow  for  a  time,  and  gradually  become  differentiated  into  the  definitive 
reticulum  of  the  thymus.  Hassall's  corpuscles  are  believed  to  represent  non- 
reticular  remnants  of  the  original  entodermal  anlages.  According  to  Ham- 
mar,  and  Bell,  these  concentric  corpuscles  are  derived  from  hypertrophic 
reticular  cells.  They  first  appear  early  in  fetal  life,  and  continue  to  form 
and  increase  in  size  during  infancy.  They  are  interpreted  by  some  as  thy- 
mic  elements  of  internal  secretion.  The  thymus  is  commonly  regarded  as  a 
hemopoietic  organ,  but  its  activity  is  limited  to  the  formation  of  lympho- 
cytes and  possibly  a  small  number  of  granulocytes,  Beard  (1900)  views  it 


THE  CAROTID  GLAND 


569 


as  the  original  source  of  leukocytes.  The  proliferative  foci  are  the  cortical 
portions  of  the  lobules;  the  medulla  does  not  correspond  to  the  germ  cen- 
ters of  lymph  nodules,  but  is  probably  an  area  of  leukocyte  dissolution. 
The  thymus  does  not  seem  to  be  an  organ  essential  to  life.  Extirpation  in 
dogs  and  guinea  pigs  is  not  followed  by  death.  However,  the  experimental 
evidence  indicates  a  reciprocal  functional  relationship  between  the  thymus 
and  certain  of  the  organs  of  internal  secretion,  especially  the  sex-glands. 
This  suggests  a  secretory  role;  a  conclusion  supported  by  the  results  of 
the  recent  experiments  of  Gudernatsch  (Amer.  Jour.  Anat.,  15,  4,  1914) 
in  which  thymus  fed  to  frog  tadpoles,  accelerated  growth,  but  suppressed 
differentiation. 

V.     THE   CAROTID   GLAND 


This  body  was  first  carefully  described  by  Luschka  (1862)  and, 
from  its  intimate  relation  to  the  blood-vessels  and  nerves,  is  also  known 
as  the  glomus  carolicum  or  ganglion  intercaroticum.  It  is  about  the 
size  of  a  rice  grain.  It 
consists  of  scattered 
masses  of  epithelioid  cells, 
usually  grouped  in  small 
spheroidal  clumps  or  'cell 
balls/  embedded  in  the 
connective  tissue  at  ilic  »\'  • 

point  of  bifurcation  of  the  ''•'">'  ^'M 

common  carotid  artery. 
Kohn  (Arch.  f.  Mik. 

Anat.,     1900)      has     de-  "^ 

scribed  four  types  of  the  chrg  **"*•••+>•" 

gland  according  to  the 
density  of  its  parenchyma 
— the  type  found  in  man 
consists  of  scattered  cell 
groups;  in  the  rabbit  they 

are  even  more  diffuse.  The  carotid  gland  of  a  cat  consists  of  a  single  cell 
mass,  while  that  of  the  ape  is  intermediate  between  that  of  the  cat 
and  man. 

The  glandular  elements  are  derived  from  embryonal  sympathetic 
ganglion  cells  (Kohn).  They  are  ovoid  cells  with  finely  granular 
cytoplasm  and  a  spheroidal,  somewhat  vesicular  nucleus.  Many  of  them 
contain  chromaffin  granules.  Because  of  its  genetic  relationship  and 


FIG.  489. — CAROTID  GLAND  OF  AN  APE. 

Chrg,  a  'chromaffin  cell';  s,  connective  tissue 
septum.  Portions  of  two  adjacent  lobules  are  in- 
cluded in  the  figure.  X  200.  (After  Kohn.) 


570  THE  DUCTLESS  GLANDS— ENDOCRIN  GLANDS 

histologic  similarity  to  a  sympathetic  ganglion,  Kohn  proposes  the 
name,  paraganglion  caroticum.  Its  function  is  obviously  similar  to 
that  of  the  other  organs  of  the  chromaffin  system,  and  probably  chiefly 
dependent  upon  the  presence  of  adrenalin. 

The  carotid  gland  is  richly  supplied  with  capillary  blood-vessels  and 
small  non-medullated  nerve  trunks.  The  capillaries  are  in  intimate 
relation  with  the  glandular  epithelium. 


VI.     THE    COCCYGEAL    GLAND 

This  small  body— 2.5   mm.  in  diameter    (Eberth) — was  discovered 
by  Luschka  in  I860.     Its  structure  closely  resembles  that  of  the  carotid 
______ gland.   It  usually  con- 

sists of  several  minute 
f^-s'"'-  groups  of  epithelioid 
cells  which  are  in  re- 
lation with  the  ter- 
minal branches  of  the 
middle  sacral  artery. 
It  is  richly  supplied 
with  broad  capillaries 
or  sinusoids  and  hence 
is  also  known  as  the 
glomus  coccygeum. 

The    parenchymal 

FIG.  490. — FROM  A  SECTION  OF  THE  COCCYGEAL  GLAND    cells  of  the  organ  are 

OF  MAN.  ovoid  elements  which 

Highly  magnified.    (After  Sertoli. .;  are    closely    packed 

about  the  walls  of  the 

blood-vessels  in  groups  or  short  columns  inclosed  by  delicate  sheaths 
of  connective  tissue.  The  origin  and  function  of  these  cells  are  un- 
known. Xo  chromaffin  cells  have  yet  been  certainly  demonstrated.  The 
organ  is  embedded  in  the  dense  connective  tissue  at  the  tip  of  the 
coccyx.  Its  general  structure  only  suggests  an  internal  secretory  function. 
According  to  Stoerck  (Arch.  mikr.  Anat,  Bd.  69,  1906),  the  cells 
of  the  coccygeal  body  do  not  give  the  pheochrome  reaction  at  any  period 
of  life.  They  are  believed  to  bear  no  genetic  relation  to  the  sympa- 
thetic nervous  system.  Schumacher  regards  the  epithelioid  cells  as 
a  transformation  of  the  smooth  muscle  cells  of  the  arterial  vessels; 


PARAGANGLIA 


571 


others  interpret  them  as  modified  endothelial  cells  of  the  blood-vessels. 
Vincent  siiggcsis  that  this  body  may  function  as  a  'safety-valve'  in  the 
course  of  the  peripheral  circulation ;  he  regards  the  balance  of  evidence 
as  against  any  function  involving  an  internal  secretion. 


Te 


VII.    PARAGANGLIA 

The  so-called  chromaffin  system  includes  besides  the  medulla  of 
the  suprarenal  and  the  carotid  gland,  other  larger  and  smaller  groups 
of  chromaffin  cells  ('pheochrome  organs')  derived  from  embryonal  sym- 
pathetic cells  and  scattered  along 
the  entire  sympathetic  nervous 
system,  the  PARAGANGLIA.  They 
are  therefore  present  in  many 
organs  which  receive  a  consider- 
able sympathetic  innervation,  e.g., 
kidney,  liver,  uterus,  testis,  etc. 
Chromaffin  tissue  composed  of 
widely  scattered  cells  is  present 
also  in  the  sympathetic  trunks, 
particularly  the  various  plexuses, 
among  the  definitive  neurons  of 
this  system. 

The  largest  paraganglia  (or- 
gans of  Zuckerkandl)  occur  in 
close  relation  to  the  inferior  mes- 
enteric  artery,  one  on  either  side. 
Other  smaller  groups  are  found 
in  relation  to  the  abdominal 
aorta.  Busachi  has  recently 


FIG.  491. — MEDIAN  SECTION  THROUGH  THE 
ANLAGES  OF  THE  HYPOPHYSIS  CEREBRI 
OF  A  10  MM.  CAT  EMBRYO.  (Bonnet.) 

Di,  diencephalon;  Te,  telencephalon ; 
Jl/,  mouth;  R,  Rathke's  pouch  (pituitary 
anlage);  /,  infundibulum.  X  50. 


(1912)  described  chromaffin  tis- 
sue in  the  human  heart;  and  Thulin  (Anat.  Anz.,  46,  22,  1914)  reports 
a  paraganglion  in  the  striped  muscle  of  the  upper  portion  of  the  esoph- 
agus of  man.  In  typical  paraganglia  the  .polygonal  cells  are  arranged 
in  irregular  cords  which  form  a  fine-meshed  network,  the  areolae  of 
which  are  occupied  by  sinusoidal  blood-vessels,  upon  which  the  cells  rest 
directly  without  the  intervention  of  a  basement  membrane.  The  spher- 
ical nucleus  is  poor  in  chromatin ;  the  roticular  cytoplasm  contains  the 
phcochrome  granules.  The  internal  secretion  <>!'  the  paraganglia  de- 


572  THE  DUCTLESS  GLANDS— ENDOCRIN  GLANDS 

pends  upon  the  adrenalin  content  of  the  granules.  Adrenalin  produces 
a  contraction  of  involuntary  muscle.  Its  function  appears  to  be  to 
maintain  the  proper  tonus  of  the  blood-vessels. 


VIII.    HYPOPHYSIS  CEREBRI 

(Pituitary  Body) 

The  HYPOPHYSIS  is  a  gland  of  the  internally  secreting  (endocrin) 
or  ductless  type.  The  secretion  passes  directly  from  the  specific  cells 
into  capillaries.  This  gland  is  a  composite  structure,  arising  from  the 
association  of  two  originally  distinct  anlages;  one  taking  origin  as  a 
median  dorsal  diverticulum  (Rathke's  pouch)  from  the  primitive  mouth, 
the  other  as  a  medial  ventral  evagination  from  the  second  cerebral 
vesicle  (third  ventricle)  or  diencephalon.  Both  components  are  thus 
ectodermal.  The  cerebral  flask-shaped  element  invaginates  the  buccal 
element  and  modifies  the  original"  bulbar  shape  of  the  latter  into 
that  of  a  cup.  The  buccal  connection  disappears,  while  the  cerebral 
connection  persists  as  the  infundibular  stalk  of  the  definitive  struc- 
ture. 

The  hypophysis  is  present  as  an  essentially  similar  organ  in  all 
craniates.  In  man  it  measures  about  12  mm.  in  the  transverse,  about 
7  mm.  in  the  sagittal,  and  about  5  mm.  in  the  vertical  diameter.  It 
has  an  inverted  mushroom  shape,  the  stalk  or  infundibulum,  a  hollow 
funnel-shaped  structure  lined  with  ependyma,  attaching  it  to  the  brain, 
while  its  head  is  lodged  in  the  sella  turcica  of  the  skull.  The  hypo- 
physis was  known  to  the  early  anatomists  as  the  pituitary  gland  (Vesal, 
1553),  and  was  supposed  to  function  as  an  excretory  organ  in  the  elimi- 
nation of  mucus  (pituita)  from  the  brain  by  way  of  the  nose.  The 
term  pituitary  gland  is  now  generally  applied  only  to  the  larger  anterior 
component  or  epithelial  lobe;  the  posterior  component  or  neural  lobe 
is  designated  the  infundibular  process;  the  term  hypophysis  is  applied 
to  the  associated  elements.  But  hypophysis  and  pituitary  body  are  still 
often  used  synonymously.  The  neural  and  glandular  tissues  are  said 
to  be  connected  with  each  other  by  means  of  nerve  fibers,  probably  sym- 
pathetic, connective  tissue,  and  blood-vessels.  Certain  investigators  have 
described  accessory  pituitary  bodies.  Thus  Haberfeld  (1909)  finds  in 
man  at  all  ages  a  'pharyngeal  pituitary,'  a  solid  cord  of  neutrophilic 
cells  about  5  mm.  in  length  immediately  behind  the  vomer.  This  is 
frequently  the  initial  seat  of  tumors. 


HYPOPHYSIS  CEREBRI  573 

Function. — Very  little  is  definitely  known  concerning  the  function  of 
the  hypophysis,  notwithstanding  extensive  investigation.  Much  of  the 
recorded  clinical  and  experimental  data  is  contradictory.  However,  the 
presence  of  the  gland  would  seem  to  be  essential  to  health,  perhaps  indis- 
pensable to  the  maintenance  of  life.  It  appears  also  that  its  two  funda- 
mental components  (anterior  and  posterior  lobes)  subserve  different  func- 
tions, and  that  pathological  alterations  in  the  gland  induce  marked 
changes  in  some  or  all  of  the  other  ductless  glands,  which  glands  appear 
to  sustain  reciprocal  functional  relationships  to  each  other.  Absence  of 
the  hypophysis  (apituitarism)  in  mammals  is  associated  with  grave  nutri- 
tive disturbances  usually  leading  to  death.  Disordered  function  (dyspitui- 
tarism)  is  accompanied  by  inordinate  enlargement  of  the  extremities 
(acromegaly)  and  gigantism,  mental  derangements,  disturbances  in  the 
sexual  organs  and  improper  metabolism  of  sugar.  Reduced  secretion 
('hypopituitarism')  of  the  posterior  lobe  leads  to  an  acquired  high  toler- 
ance for  sugars  with  the  resultant  accumulation  of  fat  (Gushing;  "The 
Pituitary  Body  and  Its  Disorders,"  1910).  Increased  secretion  may  be 
responsible  for  some  types  of  emaciation  and  for  certain  mental  distur- 
bances. Deficient  secretion  of  the  anterior  lobe  appears  to  inhibit  com- 
plete development  of  the  skeleton,  resulting  in  dwarfism  and  infantilism; 
conditions  of  superabundant  secretory  activity  (hyperpituitarism)  are  ac- 
companied by  acromegaly  and  gigantism  (Gushing).  Injection  of  extract 
of  the  posterior  lobe  (pituitrin)  into  the  blood-vessels  produces  a  rise  of 
blood  pressure  accompanied  by  diuresis,  believed  to  be  due  to  a  stimulation 
of  the  smooth  musculature  of  the  blood-vessels.  In  its  effect  upon  smooth 
muscle,  particularly  of  the  uterus,  which  it  stimulates  to  sharp  and  pro- 
longed contraction,  it  resembles  very  closely  the  secretion  of  the  suprarenal 
gland.  Pituitrin  is  now  extensively  used  in  practical  medicine  and  espe- 
cially in  obstetrics. 

The  anterior  lobe  is  believed  by  some  to  be  physiologically  inactive, 
except  in  cases  of  defective  secretion  of  the  gland,  while  others  hold  that 
the  removal  of  the  posterior  lobe  gives  rise  to  no  symptoms,  but  that  ex- 
cision of  the  anterior  lobe  produces  all  the  ill  effects  of  total  pituitary 
extirpation.  The  contradictory  results  of  experimental  work  may  be  due 
to  failure  or  inability  to  completely  separate  the  several  portions;  more- 
over, certain  elements  of  the  supposed  symptom  complex  accompanying 
hypophysectomy  may  be  due  to  mechanical  injury  to  associated  parts  of 
the  brain. 

Histologic  Structure.— The  hypophysis  is  usually  described  as 
consisting'  of  three  portions:  (1)  the  anterior  lobe  or  glandular  portion; 
(2)  the  intermediate  portion  or  boundary  zone;  and  (3)  the  posterior 
lobe,  or  nervous  portion.  The  recent  more  critical  investigation  of 


574 


THE  DUCTLESS  GLANDS— ENDOCRIN  GLANDS 


Tilney  (Internationale  Monatschrift  f.  Anat.  u.  Phys.,  Bd.  30,  1911), 
including  careful  reconstructions  of  a  number  of  mammalian  hypophyses, 
shows  that  this  description  is  incomplete.  The  form,  extent,  relation 
and  genetic  significance  of  the  pars  intermedia  had  apparently  hitherto 
not  been  fully  appreciated,  though  Herring  (1908)  had  already  called 
attention  to  the  fact  that  it  comprised  two  histologically  different  areas. 
Tilney  divides  the  hypophysis  into:  (I)  pars  neuralis  (pars  nervosa) ; 


13  15 

FIG.  492. — SAGITTAL  VIEW  OF  A  WAX  RECONSTRUCTION  OF  THE  HYPOPHYSIS  CERE- 
BRI  OF  THE  ADULT  CAT. 

1,  third  ventricle;  9a  and  6,  eminentia  saccularis;  6,  area  premammillaris;  5,  cor- 
pora mammillaria;  12,  pars  tuberalis;  8,  recessus  infundibuli;  10,  infundibulum ;  13, 
pars  infundibularis;  16,  recessus  process!  infundibuli;  11,  processus  infundibuli; 
15,  lumen  residuale;  14,  pars  distalis;  17.  recessus  tuberis;  3,  optic  chiasm.  (Tilney, 
Internat.  Monatschr.,  Bd.  30,  1913.) 


and  (II)  pars  buccalis.  The  pars  neuralis  consists  of  three  distinct 
elements:  (a)  the  eminentia  saccularis  of  the  tuber  cinereum;  (b)  the 
infundibulum;  and  (c)  the  infundibular  process.  The  pars  buccalis 
consists  of  two  elements:  (a)  the  pars  juxta-neuralis  in  close  relation 
with  and  investing  the  neural  portion;  and  (b)  the  pars  distalis.  A 
cleft,  the  residual  lumen,  remnant  of  the  original  cavity  in  the  buccal 
diverticulum,  appears  between  the  two.  Further  analysis  of  the  juxta- 
neural  portion  of  the  gland  reveals  two  histologically  different  parts: 
(1)  the  pars  infundibularis  completely  investing  the  infundibulum 


HYPOPHYSIS  CEREBRI  575 

and  the  infundibular  process;  and   (2)   the  pars  tuberalis,  which  sur- 
rounds the  eminentia  saccularis. 

The  following  outline  presents  this  analysis  in  resume: 

HYPOPHYSIS   CEREBRI 

I.  Pars  Xeuralis:    (Posterior  lobe). 

(1)  Eminentia  Saecularis. 

(2)  Infundibulum. 

(3)  Processus  infundibuli. 
II.  Pars  Buccalis  sen  Glandularis: 

(1)  Pars  juxtaneuralis.     (Intermediate  portion.) 

(a)  Pars  tuberalis. 

(b)  Pars  infundibularis. 

(2)  Pars  distalis.     (Anterior  lobe!) 

"The  pars  infundibularis  makes  its  appearance  almost  immediately 
after  the  anlage  of  the  buccal  portion  of  the  hypophysis  is  formed.  The 
pars  tuberalis  arises  as  a  relatively  late  structure.  It  has  its  origin  in  two 
secondary  diverticula  or  sprouts  from  the  body  of  the  pituitary  sac  (buccal 
evagination).  These  sprouts,  the  lateral  processes,  ultimately  fuse  with 
each  other  across  the  median  line,  displace  the  body  of  the  pituitary  sac 
ventrad  and  thus  secondarily  assume  their  juxtaneural  position.  The 
juxtaueural  portion  of  the  hypophysis  is  intimately  connected  with  the 
nSural  portion  by  means  of  nerve  fibers,  blood-vessels  and  connective 
tissue  processes.  Attempted  separation  consequently  necessarily  includes 
laceration  of  neural  elements"  (Tilney).  Accordingly  complete  removal  of 
the  pars  buccalis  would  seem  to  be  impossible  without  the  attendant  re- 
moval of  portions  of  the  pars  neuralis.  This  must  be  taken  into  account  in 
interpreting  symptoms  following  removal  of  the  anterior  lobe  of  the  hypo- 
physis. 

I.  PARS  NEURALIS  :  INFUNDIBDLUM. — This  consists  of  fusiform  and 
multipolar  neuroglia  cells  and  fibers.     A  substance  resembling  colloid  is 
also  occasionally  present.     Small  nerve  cells  have  been  reported,  but 
their  presence  seems  doubtful.     The  glia  cells  generally  have  a  single 
nucleus,  but  two  or  more  may  appear.    The  protoplasm  is  finely  granu- 
lar, and  occasionally  contains  pigment  granules,  which  seem  to  be  more 
abundant   in    aged   specimens.      Delicate  and  coarse  glia  fibers  extend 
through  the  protoplasmic  portions  of  the  cells,  frequently  terminating 
the  cell  processes  (Fig.  4%). 

II.  PARS  BUCCALIS  SKIT  GLANDULARIS:   (1)  Pars  juxianeuralis. — • 


576 


THE  DUCTLESS  GLANDS— ENDOCBIN  GLANDS 


FIG.   493.— PARS  TUBERALIS,    HYPO- 
PHYSIS OF  CAT    (Tilney.) 


(a)  Pars  tuberalis. — The  cells  of  this  portion  are  arranged  in  large 
tubular  acini;  the  lumina  may  contain  colloidal  material.  The  cells 
are  of  the  cuboidal  type,  sometimes  ciliated,  frequently  two  layers  deep. 

The  cytoplasm  of  the  cells  is  sparse, 
homogeneous  and  deeply  basophilic. 
The  nuclei  are  large  and  vesicular. 
Blood-vessels  (sinusoidal  capillaries) 
are  numerous,  and  are  said  occa- 
sionally to  contain  colloid. 

(b)  Pars  infundibularis. — Here 
the  cells  are  arranged  in  a  dense 
stratum  several  layers  deep.  Occa- 
sional acini  (cysts)  occur,  but  they 
are  smaller  than  in  the  pars  tuber- 
alis  and  are  lined  with  only  a  sin- 
gle layer  of  low  cuboidal  cells. 
These  cells  contain  large  vesicular 
centric  nuclei  surrounded  by  a  con- 
siderable layer  of  faintly  basophilic 
granular  cytoplasm.  Blood-vessels  are  very  meager  and  thin-walled. 

(2)  Pars  distalis. — This  portion  is  surrounded  by  a  robust  fibrous 
capsule  continuous  posteriorly  with  a  thinner  investment  for  the  neural 
lobe.  Delicate  trabeculae  traverse 
the  parenchyma  and  support  the 
very  abundant  plexus  of  arterio- 
venous  sinusoidal  blood  spaces.  The 
peripheral  cells  of  the  pars  distalis 
constitute  a  narrow  zone  of  almost 
exclusively  basophilic  cells.  The 
cells  of  the  main  central  portion  are 
arranged  in  dense  convoluted  anas- 
tomosing cords.  The  cords  com- 
prise axial  and  parietal  cells.  The 
parietal  cells  are  the  larger,  of 
polygonal  shape,  and  with  a  gran- 
ular cytoplasm  deeply  acidophilic. 


FIG.  494.— PARS  INFUXDIBULARIS,  HY- 
POPHYSIS OF  CAT.  (Tilney.) 


These  are  the  'eosinophilic'  or  acid- 
ophilic ('chromophiP)  cells.  The  axial  cells  are  smaller;  their  cyto- 
plasm contains  'neutrophilic'  granules.  Those  are  the  'chief/  or  'chrom- 
ophobe'  cells.  The  so-called  'chromophils'  and  'chromophobes'  of  the 


HYPOPHYSIS  CEREBRI 


577 


earlier  terminology  (Flcsch/  1880),  which  was  based  simply  upon  a 
difference  in  the  degree  of  tingibility,  probably  represent  merely  different 
functional  phases  of  the  same  cell  type.  The  classification  of  the  cells  as 
acidophils  and  basophils,  a  distinction  based  upon  a  more  precise  micro- 
chemical  difference,  accords  with  a  topographical  segregation  and  more 
probably  designates  an  actual  functional  division.  True  chromophobes, 
cells  which  stain  only  faintly  and  with  difficulty  in  either  acid  or  basic 
dyes — and  probably  functional  phases  of  acidophil  and  basophil  cells — 
appear  first  only  in  the  higher  sau- 
ropsids  (Tilney).  The  nuclei  of 
the  several  cell  types  are  large  and 
deeply  staining.  The  cells  in  great 
part  rest  directly  upon  the  endothe- 
lial  walls  of  the  capillaries.  The 
blood-vessels  are  said  to  contain 
colloid. 

Comparative  histologic  studies 
indicate  that  the  pituitary  gland 
has  a  twofold  activity,  one  part  de- 
pendent upon  the  basophils,  the 
other  upon  the  acidophils.  The 
residual  lumen  is  lined  only  with 
basophils,  and  occasionally  contains 
colloid.  Comparative  morphology 

indicates  that  the  neural  portion  may  represent  an  original  special  sense 
organ.  It  has  been  suggested  by  Tilney  (Mem.  Wistar  Inst.,  Biol.  and 
Anat.,  No.  2,  1911)  that  the  basophils  contribute  their  secretion  by  way 
of  the  residual  lumen  and  the  infundibular  process  to  the  cerebrospinal 
fluid,  and  the  acidophils  directly  through  the  blood  spaces. 

According  to  Dandy  and  Goetsch  (Amer.  Jour.  Anat.,  11,  2,  1911), 
the  pars  distalis  receives  from  eighteen  to  twenty  small  arteries  which 
converge  to  it  from  the  circle  of  Willis.  Within  the  lobe  no  true  arteries 
or  veins  occur.  The  blood  channels  are  sinusoidal  in  nature;  they  drain 
into  a  venous  circle  overlying  the  circle  of  Willis. 

The  above  description  of  the  hypophysis  is  based  largely  upon  dog 
and  cat  material.  Our  knowledge  of  the  human  hypophysis  is  less 
complete;  but  as  far  as  is  known,  the  structural  elements  are  essentially 
closely  similar. 

The  nerve  supply  to  the  hypophysis  in  the  dog  is,  according  to  Dandy 
(Amer.  Jour.  Aunt.,  l."i,  :!,  1913),  derived  from  the  carotid  plexus  of  the 


FIG.  495. — PARS  DISTALIS,  HYPOPHY- 
SIS OF  CAT.  (Tilney.) 


578 


THE  DUCTLESS  GLANDS— ENDOCRIN  GLANDS 


sympathetic  system,  which  connects  with  the  oculomotor  and  optic  nerves. 
The  innervation  of  the  anterior  lobe  is  described  as  abundant,  that  of  the 


FIG.  496.— SECTION  OP  HYPOPHYSIS  CEREBRI  OF  DOG,  SHOWING  PORTIONS  OF  PARS 
DISTALIS  (D)  OP  ANTERIOR  OR  BUCCAL  LOBE,  RESIDUAL  LUMEN  (R),  PARS  Tu- 
BERALIS  (PARS  INTERMEDIA)  (T),  PARS  NEURALIS  (/V),  AND  C,  CAPSULE. 

Note  the  abundant  large  blood  sinuses  in  the  glandular  or  buccal  portion,  and 
the  tubules  in  the  pars  tuberalis  (referring  to  the  portion  next  the  tuber  cinereum). 
The  pars  neuralis  is  largely  of  neurogliar  composition. 

posterior  lobe  as  very  scanty.     The  fibers  are  thought  to  be  secretory  in 
character. 

Dandy  (ibid.)  described  also  a  small  spherical  body  which  he  names 
parahypophysis  in  connection  with  the  under  central  surface  of  the  hypo- 


EPIPHYSIS  CEREBRI 


579 


phvsis,  resting  in  a  depression  in  the  floor  of  the  sella  turcica.  This  was 
found  in  over  eighty  per  cent,  of  dogs  examined.  It  is  interpreted  as  a 
remnant  of  the  embryonic  Ratlikc's  pouch.  It  is  said  to  vary  greatly  in 
size  and  histological  character,  occasionally  extending  to  the  'pars  inter- 
media,' and  to  have  an  individual  blood  supply  and  possibly  also  a  nerve 
supply.  A  parahypophysis  has  not  yet  been  reported  for  man. 


Fit;.  497. — FIELD  FROM  THE  CENTER  OF  A  NORMAL  CAMM:     Trppv)  PARS 
ANTERIOR  ( DISTALIS > . 

Note  the  excess  of  eosinophils  ILing  the  si.aist  s.  No  has.jphils  in  the  field, 
as  they  are  more  in  evidence  in  the  glandular  periphery.  The  central  elements  in 
the  cell  columns  arc  ncutrophilic.  (Cushing.) 

In  the  hypophysis  of  the  ox,  Wulzen  (Anat.  Eec.,  8,  8,  1914)  has 
ileM-rihed  a  cone-shaped  structure  in  connection  with  the  'pars  intermedia' 
rest-mliling  in  cellular  constitution  the  pars  glandularis  but  differing  in 
having  finer  connective  tissue  septa  and  smaller  acini. 


IX.     EPIPHYSIS   CEREBRI 

(Pineal  body) 

The  EPIPHYSTS  (pineal  body,  pineal  gland  or  conarium}  may  be 
provisionally  regarded  as  an  endocrin  gland.  Its  glandular  function 
may  be  of  importance  only  during  late  fetal  and  infantile  (or  pre- 
puberal)  life,  when  it  may  control  normal  growth.  The  mammalian 


580        THE  DUCTLESS  GLANDS— EXDOCEIX  GLANDS 

epiphysis  has  been  known  to  anatomists  as  a  probable  gland  since  the 
time  of  Galenus  (200).  It  has  excited  interest  and  been  the  subject 
of. much  speculation  for  centuries.  Descartes  (1649)  regarded  it  as 
the  seat  of  the  'soul.'  Notwithstanding  much  study,  it  is  still  but  im- 
perfectly understood,  and  even  its  histological  makeup  is  to  some  extent 
in  dispute. 

Development.— The  epiphysis  cerebri  arises  as  an  ependymal  diver- 
ticulum  from  the  roof  of  the  diencephalon.  The  apical  cells  proliferate 
and  undergo  differentiation  into  neuroglia  and  interneuroglia  cells.  The 
latter  may  perhaps  assume  secretory  activities,  but  no  convincing  cyto- 
logical  evidence  appears  indicative  of  such  function  apart  from  numerous 
melanic  granules, — which,  however,  are  present  in  all  of  the  cells  in  early 
stages  of  development — and  certain  lipoid  granules  and  spherules.  In  the 
sheep  numerous  cysts,  lined  by  tall  columnar  (ependymal)  cells  appear  at 
•half  term  (21  cm.  stage).  The  cysts  contain  a  coagulum.  The  cysts  pro- 
gressively disappear,  apparently  through  pressure  from  proliferating  cells 
without,  only  a  few  persisting  to  birth  and  occasionally  "after.  In  the  sheep 
the  cysts  arise  through  accumulations  of  fluid,  compelling  a  cellular 
arrangement  simulating  acini,  not  as  tubular  outgrowths  from  the  original 
lumen,  as  is  apparently  the  case  in  birds.  Both  melanic.  granules  and 
alveoli  (cysts)  are  more  probably  to  be  interpreted  as  of  ancestral  signifi- 
cance. As  far  as  is  known  an  epiphysis  is  present  in  all  vertebrates,  with 
the  exception  of  Myxinoides  and  Crocodilia.  No  trace  of  an  epiphysis  is 
said  to  appear  even  in  embryos  of  Crocodilia.  The  pineal  eye  of  certain 
reptiles  is  commonly  regarded  as  the  homologue  of  the  pineal  body  of 
mammals.  However,  in  the  lower  groups  of  animals  the  true  homologue  is 
generally  a  double  structure,  the  pineal  eye  developing  terminally  on  a 
secondary  anterior  evagination  from  the  base  of  the  primary  one.  This 
secondary  process  is  not  developed  in  mammals.  In  Hatteria  (a  Xew 
Zealand  'lizard')  the  pineal  eye  comes  to  the  surface  in  the  middle  of  the 
head,  and  consists  of  an  optic  cup  with  a  lens  covered  by  transparent  epi- 
dermal scales,  forming  a  cornea.  It  is  believed  to  function  only  as  a  light 
or  warmth  perceptive  organ.  An  additional  structure,  the  parapliysis, 
found  in  certain  lower  forms  and  in  the  marsupialia,  anterior  to  the  pineal 
body,  and  arising  similarly  as  an  ependymal  evagination,  is  commonly 
regarded  as  a  choroid  plexus,  evaginated  instead  of  being  invaginated,  as 
is  usually  the  case  in  mammals.  In  sheep  the  pineal  undergoes  its  greatest 
development  during  the  first  year  of  life,  approximately  fivefold. 

The  pineal  body  is  attached  to  the  posterior  portion  of  the  roof 
of  the  third  ventricle  by  means  of  the  pineal  stalk.  This  contains  the 
pineal  recess,  a  cavity  continuous  with  the  ventricle.  The  anterior  wall 


EPIPHYSIS  CEREBEI 


581 


FIG.  498. — SEMIDIAGRAMMATIO  REPRESENTATION  OP  A 
MEDIAN  LONGITUDINAL  SECTION  THROUGH  THE  EPI- 
PHYSIS OF  A  17  CM.  SHEEP  FETUS. 


of  the  stalk  is  limited  basally  by  the  liabenular  commissure,  the  posterior 
wall  by  the  posterior  commissure.  The  pineal  proper  thus  lies  under- 
neath the  posterior  end  of  the  corpus  callosum  and  rests  on  the  anterior 
pair  of  the  corpora  quadrigemiua.  It  is  a  solid  cone-shaped  structure 
enveloped  by  a  cap- 
sule of  pia  mater,  and 
more  or  less  distinctly 
lobed  (Fig.  498).  It 
measures  in  man  7 
mm.  in  length  by  5 
mm.  in  transverse 
diameter.  The  mam- 
malian pineal  is  per- 
haps rather  a  meta- 
morphosed than  a  ru- 
dimentary organ.  Its 
size  bears  no  relation 
to  the  size  of  the 
brain  or  the  size  of 
the  body;  it  is  no 
larger  in  large  than 

in  small  dogs,  for  example,  and  no  larger  in  horse  than  in  dog;  that 
of  sheep  is  about  the  size  of  that  of  man. 

Function. — Injection  of  pineal  extract  of  sheep  into  the  blood  of  cer- 
tain mammals  produces  only  very  slight  effects.  These,  however,  are  fairly 
uniform,  but  very  transient.  The  most  conspicuous  effect  is  a  slight  fall 
of  blood  pressure.  There  is  also  a  slight  improvement  in  the  beat  of  the 
isolated  cat's  heart,  a  transient  diuretic  effect  (in  rabbit)  and  a  slight  ir- 
regular respiratory  effect  (in  dog,  cat  and  sheep — Jordan  and  Eyster,  Amer. 
Jour.  Physiol.,  1911).  These  results  are,  to  some  extent,  the  reverse  of 
those  obtained  with  extracts  of  the  hypophysis,  and  suggest  a  compensatory 
or  antagonistic  regulatory  functional  relationship.  Extirpation  experi- 
ments have  not  yet  yielded  perfectly  satisfactory  results.  The  evidence, 
however,  indicates  a  functional  role  which  is  negligible  or  nil.  Clinical 
evidence  combined  with  autopsy  findings  indicate  symptom  complexes  asso- 
ciated with  pineal  tumors  or  other  structural  alterations  in  general  like, 
but  of  reverse  relationship,  to  those  present  in  case  of  hypophyseal  altera- 
tion; i.e.,  the  symptoms  of  hypopinealism  are  in  general  those  associated 
with  hyperpituitarism,  and  those  of  hyperpinealism  like  those  accompany- 
ing hypopituitarism.  The  symptoms  associated  with  morbid  conditions  of 
the  pineal  may  possibly  be  the  inherent  result  of  pressure  (or  undue  relaxa- 


582 


THE  DUCTLESS  GLANDS— ENDOCEIN  GLANDS 


tion)  upon  the  hypophysis  transmitted  through  the  third  ventricle  with 
which  both  pineal  and  hypophysis  are  connected.  Certain  symptoms  may 
also  be  due  to  a  blocking  of  the  aqueduct,  and  to  pressure  upon  the  corpora 
quadrigemina.  A  conservative  estimate  of  all  the  evidence  indicates  very 
meager,  if  any  functional  activity,  probably  never  essential  to  life.  The 
practical  absence  of  the  pineal  body  in  the  opossum  adds  further  support 
to  this  conclusion;  as  also  its  occasional  disappearance,  except  for  a  mere 
shell,  in  apparently  normal  cats.  Biedl  (1910),  however,  arrives  at  the 
conclusion  that  the  pineal  body  is  an  organ  of  internal  secretion  with 
metabolic  significance  limited  to  the  young.  Its  general  histological  struc- 
ture, and  profuse  vascularity,  certainly  suggest  a  glandular  function.  On 
the  basis  of  feeding  experiments  with  bullocks'  pineals  on  certain  labora- 
tory animals  and  mentally  defective  children,  Dana  and  Berkeley  (Med. 
Bee.,  May,  1913)  venture  to  suggest  a  relationship  of  pineal  function  in 
the  young  to  bodily  nutrition,  including  the  development  of  the  genital 
organs,  the  deposit  of  subcutaneous  fat,  general  growth  and  mental  prog- 
ress. The  pineal  is  a  common  seat  of  cysts  and  tumors,  frequently  glio- 
mata. 


, 


Histologic  Structure. — The  epiphysis  cerebri  is  divided  imper- 
fectly into  lobes  by  trabeculse  of  fibro- 

9  M  *+  ' ^  elastic  connective  tissue  provided  by  the 

pia  mater  capsule.  These  support  the 
larger  blood-vessels.  The  finer  trabeculse 
shade  into  the  fundamental  reticular  tis- 
sue which  supports  the  parenchyma  and 
the  capillaries.  The  larger  vessels  are 
surrounded  by  considerable  spaces,  per- 
haps lymphatics.  The  parenchyma  is 
aggregated  into  uncertain  follicular 
masses  and  consists  of  two  distinct  types 
of  cells:  neuroglia  and  interneuroglia 
(secretory  cells?).  The  abundant  neu- 
roglia fibers  appear  to  blend  intimately 
with  the  connective  tissue  framework  of 
the  structure.  The  interneuroglia  cells 
are  oval  and  polygonal,  with  a  vesicular 
nucleus,  and  apparently  lacking  a  cell 
membrane.  The  neuroglia  cells  are 
fusiform  or  stellate,  with  denser,  more 
deeply  staining  nuclei,  and  glia  fibers  in  the  cytoplasm.  Transition 


I 

FIG.  499. — CELLS  FROM  THE  PI- 
NEAL BODY  OF  A  11  CM.  SHEEP 

FETUS. 

a,  two  neuroglia  and  one  inter- 
r2uroglia  cell;  b,  various  forms  and 
sizes  of  intracellular  melanic  gran- 
ules. X  1500. 


EPIPHYSIS  CEREBRI 


583 


forms  are  abundant.  In  young  sheep  both  types  of  cells  are  charac- 
terized by  pigment  granules;  in  aged  specimens  the  pigment  is  for 
the  most  part  present  in  the  shape  of  extracellular  clumps.  Also  in 
these  stages  the  connective  tissue  is  relatively  much  more  abundant, 


t,        * 

FIG.  500. — PHOTOMICROGRAPH  OF  A  PERIPHERAL  PORTION  OF  THE  PINEAL  BOOT 
OF  A  21  CM.  SHKKP  FETUS,  SHOWING  SEVERAL  CYSTS  AND  VASCULAR  TRABECUL.E, 
AND  AN  ENORMOUS  NUMBER  OF  INTRACELLULAR  MELANIC  GRANULES.  X  250. 

and  the  interneuroglia  cells  rare.  The  intcrneuroglia  cells  are  prob- 
ably less  highly  differentiated  neuroglia  cells,  both  types  originally 
arising  from  ependyma.  The  interneuroglia  cells  also  contain  granules 
and  vacuoles  of  a  lipoid  nature,  perhaps  degenerative  in  significance; 
no  pheochrome  granules  are  demonstrable.  Involution  begins  about 
the  age  of  7  years  in  man  and  <>n«ls  about  the  age  of  puberty,  though 
regressive  histo logical  changes  proceed  throughout  life.  Adult  corpora 
pinealia  present  very  variable  historic  pictures. 


584 


THE  DUCTLESS  GLANDS— ENDOCRIN  GLANDS 


FIG.  501. — PHOTOMICROGRAPH  OF  PERIPHERAL  REGION  OF  PINEAL  BODY  OF  A 
YEARLING  SHEEP,  TO  SHOW  THE  CHARACTER  OF  THE  PARENCHYMA,  THE  NEUROGLIA 
CELLS  AND  FIBERS,  AND  THE  INTERNEUROGLIA  CELLS. 

In  older  specimens  large  lamellated  masses  of  brain  sand  (acervulus 
cerebri)  appear,  consisting  chiefly  of  calcium  carbonate  and  magnesium 
phosphate.  These  specimens  are  also  characterized  by  large  edematous 


FIG.  502. — Two  NEUROGLIA  AND  THREE  INTERNEUROGLIA  CELLS  FROM  THE  PINEAL 
BODY  OF  A  LAMB.     X  1500. 


EPIPIIYSIS  CEEEBRI 


585 


areas.  The  intern euroglia  cells  have  heen  variously  designated  as 
•pineal  cells/  'epithelial  cells/  'lymphoid  cells'  and  'secretory  cells/  Cer- 
tain workers  claim  to  have  distinguished,  in  certain  mammals,  two  types 
of  cells,  basophils  and  acidophils.  Occasionally  smooth  and  striped 
muscle  fibers  have  also  been  described  in  a  few  forms  (e.g.,  ox).  No 
nerve  cells  are  demonstrable.  Sympathetic  nerves  accompany  the  blood- 
vessels; and  a  few  of  the  medullated  type  are  found  near  the  attached 


FIG.  503. — CELLS  FROM  PINEAL  OF    YEARLING    SHEEP. 

A,  neuroglia  cell  and  fibers;  B,  interneuroglia  cell  with  melanic  pigment  granules. 
X  1500. 


port  inn,  probably  taking  origin  from  the  habenular  and  posterior  com- 
missures. The  blood  supply  is  very  profuse.  It  takes  origin  from 
the  pial  \essels  which  are  in  union  with  the  blood-vessels  of  the  tehi 
choroidea  anteriorly.  The  vessels  follow  the  ramifications  of  the  pial 
septa.  In  the  sheep  the  capillaries  frequently  terminate  in  the  form 
of  tangled  loops  or  'glomeruli'  within  spaces  surrounded  by  more  com-« 
pact  parenchyma  ('follicles').  Cross  sections  of  the  coarser  trabecuku 
show  a  pair  of  vascular  comites. 

The  dependence  of  normal  liver  function  upon  the  integrity  of  the 
ductless  glands   is  indicated  by  derangements   following  their  removal 
(\Yhipple  and  Christian,  Jour.  Exp.  Med.,  29,  3,  1914).     Many  other 
37 


586 


THE  DUCTLESS  GLANDS— ENDOCRIN  GLANDS 


organs  (e.g.,  brain,  and  digestive  system)  no  doubt  hold  a  similar  de- 
pendence upon  the  secretions  (hormones)  of  the  ductless  glands.  More- 
over, the  ductless  glands  themselves  seem  to  sustain  interdependent 
relationships  among  themselves  and  with  the  genital  glands. 


FIG.  504.— SECTION  OF  PINEAL  BODY  OF  AN  OLD  SHEEP,  SHOWING  'BRAIN  SAND' 
(ACERVULUS)  IN  THE  PARENCHYMA. 


(For  recent  reviews  of  literature  on  the  epiphysis  cerebri  see  Kidd, 
"The  Pineal  Body :  a  Review,"  Re.  Neur.  Psyc.,  Jan.  and  Feb.,  1913 ;  and 
Jordan,  ''Results  of  Recent  Studies  of  the  Mammalian  Epiphysis  Cerebri," 
Trans.  Amer.  Micr.  Soc.,  31,  4,  1912.) 


CHAPTER  XVII 
THE  NERVOUS  SYSTEM 


THE  DEVELOPMENT  OF  THE  NERVOUS  SYSTEM 

The  first  external  evidence  of  the  beginning  of  the  nervous  system  is 
the  appearance  of  a  median  longitudinal  furrow  in  the  dorsal  (neural) 
ectoderm  of  the  very  young  embryo 
(about  the  fifteenth  day  in  man). 
This  is  known  as  the  neural  or 
medullary  groove.  Still  earlier 
stages,  as  revealed  in  sections,  in- 
clude first  an  increase  in  height  of 
the  ectodermal  cells  to  form  an  axial 
plate  of  cuboidal  cells,  the  neural 
plate;  and  secondly  the  conversion  of 
this  simple  layered  plate  into  a  struc- 
ture of  several  strata  of  cuboidal 
cells,  which  structure  meanwhile 
forms  the  floor  and  lateral  walls  of 
the  developing  neural  groove.  The 
neural  plate  apparently  grows  more 
rapidly  laterally  causing  thus  a  pro- 
gressive elevation  of  its  borders,  the 
neural  folds,  and  producing  in  con- 
sequence a  gradually  deepening  neu- 
ral groove  (Fig.  506).  According  to 
Glaser  (Anat.  Rec.,  8,  12,  1914),  the 
inequality  in  growth  between  neural 
plate  and  the  adjacent  ectoderm 
which  causes  folding  is  due  to  great- 
er water  absorption  on  the  part  of 
the  plate.  By  continuation  of  this 
process  of  unequal  growth  medially 
and  laterally,  the  folds  finally  meet 

in  the  dorsal  mid-line  and  fuse  to  form  the  neural  tube.  On  both  sides  of 
the  lino  of  fusion  a  group  of  ectodermal  cells  appears,  the  neural  or  gan- 
ylionic  crest,  from  which  arise  the  neurons  of  the  dorsal  and  sympathetic 

687 


FIG.  505.— HUMAN  EMBRYO  2  MILLI- 
METERS LONG.  (Graf  Spee.)    X  30. 

Am,  amnion;  C,  chorion;  C.V.,  chori- 
onic  villi;  Bs,  body  stalk  (embryo- 
phore) ;  Mg,  medullary  groove;  We,  neu- 
renteric  canal;  Ps,  primitive  streak; 
Ys,  yolk-sac.  (From  Williams.) 


588 


THE  NERVOUS  SYSTEM 


ganglia,  and  the  neurolemma  (sheath)  cells  of  both  the  afferent  and  efferent 
fibers  of  the  dorsal  and  ventral  roots  respectively.  The  neural  tube  (canal) 
is  originally  of  approximately  uniform  caliber  throughout;  but  shortly  the 


Am. 


Eel 


FIG.   506. — TRANSECTION   THROUGH   THE   GUAF   SPEE   EMBRYO  SHOWN   IN   THE 
PRECEDING  FIGURE. 

Am,  amnion;  ect,  ectoderm;  mes,  mesoderm;  ent,  entoderm;  M,  medullary  groove. 
(From  Williams.) 


cephalic  end,  by  a  series  of  processes  involving  dilatations,  constrictions, 
foldings  and  fusions,  develops  into  the  brain ;  while  the  caudal  portion  gives 
rise  to  the  spinal  cord. 


Ectoderm 

Ganglionic  ridge 


..  Myotome 


FIG.  507. — THREE  SUCCESSIVE  STAGES  IN  THE  PROCESS  OF  CLOSURE  OF  THE  MED- 
ULLARY (NEURAL)  GROOVE  TO  FORM  THE  MEDULLARY  (NEURAL)  CANAL  AND 
NEURAL  (GANGLIONIC)  CRESTS. 

(From  Barker,  after  M.  von  Lenhossek.) 


THE  DEVELOPMENT  OF  THE  NERVOUS  SYSTEM 


589 


These  gross  developmental  changes — more  appropriately  considered  in 
detail  in  works  of  Embryology — involve  histogenetic  processes  in  the  walls 
of  the  canal.  The  earlier  of  these  processes  are  essentially  alike  in  both 
cerebral  and  spinal  portions  of  the  canal.  Originally  the  ectodermal  layer, 
which  subsequently  forms  the  wall  of  the  tube, 
consists  of  a  single  layer  of  cuboidal  cells  similarly 
undifferentiated.  Shortly  spherical  and  oval  ger- 
minal cells  appear  among  the  primitive  ependymal 
cells.  These  indifferent  cells  migrate  peripherally 
so  that  two  layers  can  now  be  distinguished  in  the 
wall;  an  inner  nuclear  and  an  outer  non-nuclear  or 
marginal  layer.  Cell  boundaries  have  meanwhile 
become  obliterated  and  the  entire  wall  is  now  essen- 
tially a  dense  syncytium.  Still  later  the  syncytium 
assumes  a  looser  texture,  forming  the  myelospon- 
gium,  and  the  indifferent  germinal  cells  give  rise 
to  two  types  of  cells :  the  neuroblasts,  from  which 
differentiate  the  neurons;  and  the  spongioblasts, 
from  which  the  neuroglia  cells  and  fibers  develop. 
Shortly  after  the  time  when  neuroblasts  and 
spongioblasts  first  become  distinguishable  the  wall 
of  the  neural  tube  can  be  conveniently  divided  into 
three  zones:  (1)  the  ependymal  layer,  forming  in- 
ternally also  a  limiting  membrane;  (2)  the  inter- 
mediate, middle,  nuclear  or  mantle  layer,  containing  neuroblasts,  spongio- 
blasts and  indifferent  cells;  and  (3)  the  outer  non-nuclear  or  marginal 
layer,  bounded  externally  by  an  outer  limiting  membrane.  A  glia  frame1- 

work  pervades  the  entire  width  of 
the  wall. 

Neuroglia  cells  differentiate 
from  spongioblasts  by  a  process 
involving  chiefly  the  formation  of 
glia  fibers  in  their  exoplasm. 
These  fibers  apparently  arise  from 
spongioplasmic  fibrils  of  the  pro- 
toplasm. Many  glia  fibers  subse- 
quently become  disposed  extracel- 
lularly.  The  primitive  ependymal 
cells  become  greatly  modified  into 
stout,  slightly  branching  fibers  ex- 
tending through  the  width  of  the  walls  of  the  neural  tube.  The  main  body, 
of  columnar  shape*  with  its  nucleus  and  a  distal  tuft  of  cilia,  retains  its  cen- 
tral position  and  forms  an  ependymal  lining  for  the  spinal  canal  and  the 
ventricles  of  the  brain.  The  several  neuroglia  constituents  (astrocytes  and 


FIG.  503. — CELL  LIN- 
ING THE  NEURAL 
CANAL  OF  THE  NEW- 
LY-HATCHED RAIN- 
BOW TROUT,  SHOW- 
ING MITOCHONDRIA 
IN  AN  EMBRYONIC 
NERVE  CELL. 

Moves'  technic.     X 
2000. 


FIG.  509. — SECTION  THROUGH  MEDULLARY 
PLATE  OF  A  RABBIT  EMBRYO. 

The  cells  include   a   large  round  ger- 
minal cell.     (After  His.) 


590 


THE  NERVOUS  SYSTEM 


glia  fibers)   form  a  loose-meshed  syncytium,  the  myelospongium,  for  the 
support  of  the  developing  neuroblasts.    Peripherally  it  is  of  denser  texture 
and  relatively  free  of  nuclei,  and  is  designated  the  marginal  velum.    Coin- 
cident   with   this    process    of   neuroglia 
histogenesis,    the    neuroblasts     enlarge, 
proliferate  extensively  and  differentiate 
into  neurons,  their  processes — axon  and 
dendrons — arising  as   sprouts   from  the 
originally  spherical  neuroblasts. 

The  motor  neurons  remain  located 
in  the  ventral  horn  of  the  spinal  cord 
(Fig.  515),  their  axons  (efferent  fibers) 
passing  out  through  the  ventral  root  to 
unite  with  the  fibers  of  the  dorsal  root 


FIG.  510. — SECTION  THROUGH  MEDULLARY 
PLATE  OF  CLOSING  NEURAL  GROOVE  OF 
RABBIT  EMBRYO. 

Two  germinal  cells  are  visible.     (After 
His.) 


FIG.  511. — SECTION  THROUGH 
WALL  OF  LATER  NEURAL 
TUBE  OF  RABBIT  EM- 
BRYO, SHOWING  A  STAGE 
IN  THE  DIFFERENTIATION 
OF  THE  EPENDYMA  CELLS 
AND  THE  FORMATION  OF  A 
MYELOSPONGIUM. 

(After  His.) 


to  form  a  spinal  nerve.  The  sensory  neurons  arise  external  to  the  cord 
from  neuroblasts  of  the  linear  neural  crests,  and  migrate  some  distance 
ventrolaterally,  where  they  aggregate  into  metameric  oval  masses  which 
differentiate  into  the  spinal  ganglia.  The  differentiation  process  includes 
both  capsule  and  neuron  formation.  The  sensory  neuron  located  in  the 
dorsal  (spinal)  ganglia  is  also  originally  spherical  or  oval;  subsequently  it 
becomes  bi-polar;  and  finally,  by  a  process  involving  the  retraction  of  the 
cell  body  (cyton)  from  its  two  processes  and  the  fusion  of  these  processes 
proximally,  if;  becomes  a  unipolar  cell.  The  definitive  axon  thus  divides  in 
the  manner  of  a  T  or  Y.  Its  central  process,  or  axon  proper,  passes  into 
the  dorsolateral  portion  of  the  cord  as  an  afferent  fiber  and  here  makes 


THE  DEVELOPMENT  OF  THE  NERVOUS  SYSTEM 


591 


contact  through  a  telodendrion  either  directly  or  indirectly  (through  asso- 
ciation neurons)  with  the  dendrons  of  motor  neurons.  Its  peripheral 
process  is  to  be  regarded  as  the  dendron,  modified  structurally  so  as  to  be 
essentially  identical  with  the  axon. 

The  sympathetic  may  be  regarded  as  a  cenogenetic  addition  to  the 
cerebrospinal  nervous  system.     Ontogenetically  it  appears  in  man  at  tho 


FIG.  512. — SECTION  OF  WALL  OP  FORE- 
BRAIN  OF  FOUR-DAY  CHICK  EMBRYO. 

A,  apolar  neuroblast;  B,  bipolar  neuro- 
blast;  a,  the  beginning  of  the  sprouting  of 
the  axon;  c,  axons,  showing  the  terminally 
expanding  growth  area  ('cone  of  growth'). 
Cajal's  silver  technic.  (Heidenhain,  after 
Cajal.) 


FIG.  513. — DIAGRAM  OF 
A  TRANSECTION  OF 
THE  SPINAL  CORD  OF 
AN  EARLY  EMBRYO, 
SHOWING  THE  MIGRA- 
TION OF  NEUROBLASTS 
TOWARD  THE  MARGI- 
NAL VEIL,  AND  THE 
VENTRAL  NERVE 
ROOT. 

o,  neural  canal;  b,  ven- 
tral root.      (After  His.) 


beginning  of  the  fifth  week  (7  mm.  embryo).  Phylogenetically,  it  first 
appears  in  cyclostomes.  Kuntz  (Jour.  Comp.  Neur.  and  Psyc.,  29,  3,  1910) 
traces  the  neurons  of  the  sympathetic  trunks  and  the  prevertebral  plexuses 
to  neuroblasts  in  both  the  neural  crest  and  the  medullary  wall,  from  whence 
they  migrate  by  both  the  dorsal  and  ventral  nerve  roots.  The  neurolemma 
cells,  as  also  the  capsular  elements  of  the  sympathetic  neurons,  arise  from 
'indifferent'  cells  which  migrate  from  these  same  locations  and  proliferate 
and  differentiate  along  their  course.  The  cardiac  plexus  and  the  sympa- 
thetic plexuses  in  the  walls  of  the  visceral  organs  (terminal  plexuses ;  'vagal 
sympathetic'  plexuses — Kuntz)  have  their  origin,  according  to  Kuntz,  in 
nervous  elements  which  migrate  from  the  hind-brain  and  the  vagus  gan- 


592 


THE  NEEVOUS  SYSTEM 


glia  along  the  fibers  of  the  vagus  nerves.  Kuntz  believes  that  'indirect 
embryological  and  anatomical  evidence  warrants  the  conclusion  that  the 
sympathetic  excitatory  neurons  arise  from  cells  which  migrate  from  the 
neural  tube  along  fibers  of  the  motor  nerve  roots,  while  the  sympathetic 
sensory  neurons,  wherever  such  neurons  exist,  arise  from  cells  which 

migrate  from  the  cerebrospinal 
ganglia.'  However,  according 
to  Carpenter  (1914)  the  autono- 
mic  neurons  show  no  distinct 
differences  from  the  standpoint 
of  their  chromophilic  content. 
Since  such  differences  are  con- 
spicuous between  the  sensory 
and  motor  neurons  of  the  cere- 
brospinal system  (Malone),  this 
observation  arouses  skepticism 
regarding  the  presence  of  sen- 
sory sympathetic  ganglion  cells. 
The  primary  cerebral  divi- 
sions (Fig.  516)  and  their  ma- 
jor adult  derivatives  are  enu- 
merated in  the  appended  out- 
line. The  microscopic  anat- 
omy of  their  definitive  condi- 
tion lies  outside  the  scope  of 
this  book.  These  matters  are 
more  appropriately  treated  in 
special  text-books  of  Neurology 
(e.g.,  Quain's  "Anatomy,"  Vol. 
Til,  1908;  and  Villiger's  "Brain 
and  Spinal  Cord,"  translation 


FIG.  514. — TRANSECTION  OF  THE  SPINAL 
CORD  OP  A  HUMAN  EMBRYO  OF  FOUR 
WEEKS. 


The  central  canal  is  immediately  sur- 
rounded by  ependyma  cells.  The  peripheral 
nerve  cells  are  shown  on  the  left  of  the  figure. 
The  ventral  nerve  roots  are  already  pushing 
outward  from  the  primitive  cord,  d,  dorsal; 


v,  ventral  nerve  roots.     (After  His.)  by  Tiersol,  1912)  and  constitute 

the  work  of  a  separate  course. 

Likewise  the  developmental  history  is  more  advantageously  considered  in  a 
special  course  in  Embryology. 

This  work  will  include  only  the  histology  of  sections  of  the  spinal 
cord ;  and  that  of  the  cerebellar  and  cerebral  cortex. 


FIG.  515. — TRANSECTION  OF  THE  SPINAL  CORD  OF  AN  EMBRYO  CHICK. 

c.  rod.  ant.,  axons  to  the  ventral  roots;  c.  rod.  post.,  axons  to  the  dorsal  roots; 
col,  collateral  from  an  axon  back  to  the  gray  matter;  gg,  dorsal  root  ganglion;  roc. 
ant.,  ventral  root;  roc.  post.,  dorsal  root.  (After  van  Gehuchten.) 


Head/a 


Neuropore 


Anterior  cerebral 

I  vesicle,  or  pros- 

encephalon 


Pharynx  - 


Vitellin    iein~ 


Middle     cerebral 

vesicle,  or  mes- 
encephalon 

Posterior  cerebral 

vesicle,  or  rhomb- 
encephalon 


FIG.  516. — RECONSTRUCTION  OF  THE  ANTERIOR  PORTION  OF  THE  BODY  OF  A  YOUN 
CHICK  EMHKYO,  SKKN    HIOM   THE    DORSAL  SURFACE.      (After  Kollmann.) 


DERIVATIVES  OF  THE  NEURAL  TUBE 


A.  MYELON 

(spinal  cord) 


I.  RHOMBENCEPHALON 

(rhomboid  brain) 


II.  MESENCEPHALON 

(mid  brain) 


1.  Sacral 

region 

2.  Lumbar 

region 

3.  Thoracic 

(dorsal) 
region 

4.  Cervical 

region 


(a)  MYELENCEPHALON  /   5.  Medulla 

(after  brain)  \  Oblongata 


(b)  METENCEPHALON 
(hind  brain) 


(c)  MESENCEPHALON 

(mid  brain) 


III.  PROSENCEPHALON 
(fore  brain) 


(d)  DIENCEPHALON 

(interbrain  or 
'tween  brain) 


(e)  TELENCEPHALON 
(end  brain) 


594 


f  G.  Pons  Varolii 
\  7.  Cerebellum 


.  Kegion  of 
the  crura? 
cerebri 

(brain  stem) ; 
corpora 
quadrigemina 

Region  of 
the  optic 
thalami 
(basal  nuclei) 

10.  Optic  tract 

(primitive  opti< 
evaginations) 

11.  Posterior 

lobe  of 

hypophysis 

cerebri 

12.  Pineal  body 

13.  Cerebral 

cortex 
(pallium) 

14.  Corpora 

striata 

15.  Olfactory  lobes 


596  THE  NEEVOUS  SYSTEM 

THE  SPINAL  CORD 

STRUCTURE 

The  spinal  cord  (Fig.  517)  consists  of  a  considerable  mass  of  central 
gray  matter  which  is  surrounded  by  a  layer  of  medullated  nerve  fibers, 
the  white  matter. 

The  gray  matter  comprises  two  lateral  portions  united  by  a  central 
commissure  (gray  commissure)  in  transverse  section  resembling  the 
letter  H.  Each  lateral  portion  includes  a  ventral  and  a  dorsal  horn 
with  an  intervening  deeper  portion,  the  central  mass  or  'intermediate 
zone'  of  Golgi.  Each  horn  or  cornu  ends  in  a  head  or  caput  united 
with  the  intermediate  portion  or  basis  cornu  by  a  neck  or  cervix  cornu. 

The  ventral  is  somewhat  broader  than  the  dorsal  horn.  Its  cells 
supply  axons,  which,  after  uniting  into  bundles,  pass  ventralward 
through  the  white  matter  to  form  the  ventral  (anterior)  nerve  roots. 

The  spinal  cord  may  be  considered  as  consisting  of  ontogenetic 
segments  whose  number  corresponds  to  the  number  of  the  spinal  nerves. 
Hence  each  segment  contains  the  ventral  horn  cells  whose  axons  form 
the  ventral  root  of  the  corresponding  spinal  nerve. 

In  an  entirely  similar  manner  the  dorsal  horns  of  the  gray  matter 
receive  a  large  portion  of  the  incoming  fibers  of  the  dorsal  roots,  which 
in  large  part  form  end  brushes  around  the  cells  of  the  dorsal  horns 
and  the  intermediate  zone  (Fig.  518). 

The  dorsal  roots  enter  through  a  distinct  longitudinal  groove,  the 
dorsolateral  sulcus.  At  the  exit  of  the  ventral  roots  there  is,  how- 
ever, only  a  broad,  shallow  indentation,  these  roots  making  their  exit 
in  isolated  bundles  distributed  through  a  vertical  plane  of  considerable 
width.  The  dorsal  root  fibers  of  each  segment,  on  the  other  hand,  enter 
in  a  single  compact  mass. 

The  gray  matter  consists  of  a  dense  tangle  of  nerve  cells  and  non- 
medullated  fibers,  both  axons  and  dendrons,  together  with  neuroglia 
and  blood-vessels.  The  fibers  of  a  given  area  are  derived  not  only 
from  nerve  cells  in  their  immediate  vicinity,  but  also  include  many 
processes  which  come  from  very  distant  regions.  The  gray  reticulum 
is  thus  supplied  from  fibers  of  the  ventral  and  dorsal  nerve  roots,  to- 
gether with  innumerable  collaterals,  not  only  from  the  root  fibers,  but 
more  especially  from  those  fibers  which  collectively  form  the  many 
large  tracts  passing  up  and  down  the  spinal  cord  and  placing  each  seg- 


597 


598  THE  NERVOUS  SYSTEM 

ment  in  communication  with  many  other  levels  of  both  the  spinal  cord 
and  brain. 

The  center  of  the  gray  commissure  contains  the  central  canal  which 
lies  in  the  axis  of  the  spinal  cord  and  is  continuous  above  with  the  ven- 
tricles of  the  brain.  It  represents  the  remains  of  the  fetal  neural  canal ; 
and  in  the  young  subject  is  still  patent,  filled  with  cerebrospinal  fluid, 
and  lined  by  columnar  cells  which  are  frequently  ciliated.  In  older 
subjects  the  cells  of  the  lining  epithelium  have  usually  lost  their  cilia, 
and  the  lumen  of  the  canal  is  more  or  less  filled  by  cell  proliferation 
which  involves  not  only  the  lining  epithelium  but  also  the  surrounding 
glia  cells.  The  central  canal  is  immediately  surrounded  by  a  peculiar 
gelatinous  tissue  in  which  are  many  glia  cells.  This  mass  is  called  the 
substantia  gelatinosa  centralis.  A  similar  area  of  gelatinous  tissue  occurs 
near  the  extremity  of  the  dorsal  horns,  and  is  called  the  substantia 
gelatinosa  Rolandi.  The  latter,  however,  is  said  to  contain  only  a 
scanty  supply  of  neuroglia. 

The  white  matter  forms  a  covering  or  shell  around  the  central 
gray  mass.  It  increases  in  thickness  from  below  upward.  This  pecu- 
liarity is  the  result  of  the  progressive  influx  of  centripetal  fibers,  and 
a  corresponding  contribution  of  centrifugal  fibers,  through  the  spinal 
nerves  of  each  successive  segment. 

The  dorsal  median  septum  extends  inward  from  the  shallow  sulcus 
on  the  dorsal  surface  of  the  spinal  cord  to  the  central  gray  commissure, 
and  divides  the  dorsal  mass  of  white  matter  into  two  white  columns, 
lying  on  either  side  of  the  median  line,  and  bounded  laterally  by  the 
dorsal  horns  of  gray  matter  and  the  dorsal  nerve  roots.  The  ventral 
median  sulcus  in  a  similar  manner,  splits  the  ventral  portion  of  white 
matter  into  the  two  ventral  white  columns.  This  sulcus,  however, 
does  not  penetrate  all  the  way  to  the  gray  commissure  but  leaves  an 
interval  of  white  matter  containing  many  transverse  and  obliquely 
disposed  nerve  fibers.  The  ventral  or  white  commissure  thus  formed 
connects  the  two  ventral  columns  of  white  matter. 

The  spinal  cord  is  thus  divided  into  two  lateral  and  symmetrical 
halves  by  a  plane  passing  through  the  ventral  and  dorsal  median  sulci 
and  the  central  canal.  Each  lateral  half  includes  a  central  curved  mass 
of  gray  matter  completely  surrounded,  except  at  the  gray  commissure, 
by  the  white  matter.  The  latter  is  subdivided  into  a  ventral,  lateral, 
and  dorsal  column,  each  of  which  extends  the  entire  length  of  the 
spinal  cord  and  is  apparently  (to  the  naked  eye  only)  continuous  above 
with  a  similar  column  in  the  medulla  oblongata. 


THE  SPINAL  COED  599 

The  ventral  white  column  is  included  between  the  ventral  median 
sulcus  and  the  ventral  gray  horns  and  nerve  roots;  the  lateral  columns 
extend  from  the  ventral  roots  in  front,  around  the  lateral  surface  of 
the  spinal  cord,  to  the  dorsal  roots;  the  dorsal  columns  are  included 
between,  the  dorsal  horns  of  gray  matter  and  dorsal  nerve  roots,  and  the 
dorsal  median  septum. 

Each  of  these  columns  of  white  matter  is  again  subdivided  by 
neurogliar  septa  of  variable  size  and  number,  which  extend  inward 
from  the  pia  mater  for  a  considerable  distance.  Such  septa  may  even 
penetrate  all  the  way  to  the  central  gray  matter.  One  of  these  septa, 
the  paramedian  septum,  more  constant  than  the  others,  subdivides  the 
dorsal  column  into  two  portions,  a  dorsomedial  and  a  dorsolateral 
column,  or  the  funiculus  gracilis  (column  of  Goll),  and  the  funiculus 
cuneatus  (column  of  Burdach)  of  the  upper  portions  of  the  cord. 

In  the  ventral  white  column  two  chief  fiber  tracts  are  recognized: 
a  narrow  median,  the  anterior  or  direct  pyramidal  tract;  and  a  more 
lateral  larger  anterior  ground  bundle.  In  the  lateral  column  four  main 
tracts  are  recognized :  three  lateral,  including  an  upper  crossed  pyram- 
idal tract,  a  middle  direct  cerebellar  tract,  and  a  lower  or  Gower's 
column;  and  a  large  medial  lateral  ground  bundle  (Fig.  518).  These 
tracts  .do  not  possess  sharp  boundaries.  Moreover,  the  ground  bundles 
at  least  are  composite.  The  several  elementary  tracts  contain  fibers 
passing  either  from  the  periphery  to  the  brain  along  the  cord  (ascending 
•fibers]  or  from  the  brain  through  the  cord  to  the  periphery  (descending 
fibers],  or  fibers  connecting  brain  and  cord  or  different  segments  of 
the  cord.  For  a  detailed  description  of  the  constitution  of  these  fiber 
tracts  reference  must  be  made  to  the  systematic  text-books  on  the  nervous 
system. 

The  larger  blood-vessels  are  distributed  along  the  fibrous  septa, 
taking  their  origin  from  the  vessels  of  the  pia  mater ;  the  most  of  them 
are  distributed  to  the  white  matter,  but  to  some  extent  they  also  supply 
the  gray  matter. ' 

The  entire  surface  of  the  spinal  cord  presents,  just  beneath  the  pia 
mater,  a  thin  superficial  layer  or  marginal  veil  of  glia  tissue.  In  the 
brain  this  layer  is  somewhat  exaggerated  in  thickness. 

THE  REGIONS  OF  THE  SPINAL  CORD 

The  varying  number  of  fibers  which  are  given  off  at  different  levels 
of  the  spinal  cord  results  in  considerable  differences  in  size  in  its  sev- 
eral portions.  By  means  of  these  peculiarities,  as  well  as  by  the  spinal 


GOO 


THE  NEKVOUS  SYSTEM 


w>- 


FIG.  519. — TRANSECTION  OF  THE 
SPINAL  CORD  OF  A  CHILD, 
THIRD  SACRAL  SEGMENT. 

Weigert  stain.     X  7. 


nerve  roots  to  which  they  give  origin,  we  distinguish  a  sacral,  lumbar, 
thoracic,  and  cervical  region.  Each  of  these  regions  presents  certain 
more  or  less  important  morphological 
characteristics. 

In  the  sacral  region  the  investment 
of  white  matter  is  very  thin,  the  gray 
matter — though  actually  less  in  amount 
than  in  the  more  cephalad  regions — ap- 

\  ^'T  '  •'?!?-  'I  '^tv'.\l ;"'^  ••%/*  pear  ing  largo  by  comparison.  Both  the 
^fe-|-''fcl^l :  K,  r':JU^  ventral  and  dorsal  horns  of  gray  matter 
are  short  and  thick.  The  substantia 
gelatinosa  Eolandi  is  of  considerable 
volume.  The  cell  groups  in  the  ventral 
horns  of  this  region  are  a  ventromedial 
and  a  dorsolateral. 

The  cord  as  a  whole  is  small  and  its  transection  nearly  circular  in 
outline.     The  five  segments  of  this  region  contain  the  neuron  centers 
for  the  urinary  bladder,  the  anus,  some  of  the  musculature  of  the  lower 
limbs,  and  the  sensory  reflexes 
of  the  perineum   and  genito- 
urinary  organs. 

Below  the  sacral  region  the 
spinal  cord  tapers  rapidly 
(conus  medullaris)  and  is  con- 
tinued downward  for  a  consid- 
erable distance  as  the  filum 
terminals.  The  surrounding 
leash  of  lumbar  and  sacral 
nerve  roots  forms  the  cauda 
equina.  The  fibrous  mem- 
branes which  surround  the 
cord  continue  even  farther 
downward  in  the  medullary 
canal  to  form  the  central  liga- 
ment, which  is  finally  attached  to  the  sacrum  or  coccyx. 

In  the  lumbar  region  there  is  a  distinct  enlargement,  chiefly  in- 
volving the  gray  substance,  which  here  includes  the  immense  number  of 
cells  of  the  ventral  horns  whose  'motor'  fibers  enter  the  large  lumbar 
nerve  trunks  for  the  supply  of  the  lower  limbs.  These  nerve  trunks 
also  supply  to  the  cord  a  great  number  of  centripetal  or  sensory  fibers 


FIG.  520. — TRANSECTION  OF  THE  SPINAL 
CORD  OF  A  CHILD,  FIFTH  LUMBAR  SEG- 
MENT. 

Weigert  stain.     X  7. 


THE  SPINAL  COED  601 

which  enter  the  dorsal  and,  later  (through  secondary  neurons),  the 
lateral  columns;  thus  both  of  these  columns  are  of  large  size  in  and 
above  the  lumbar  region.  The  dorsomedial  column  in  this  region  at- 
tains an  appreciable  size,  and  a  distinct  pial  septum  marks  its  lateral 
boundary. 

The  spinal  cord  is  now  nearly  circular  in  transection,  its  ventro- 
dorsal  being  perhaps  slightly  less  _^-*— -  ^-•J^~ 

than  its  transverse  diameter  (10  >  •  ""•  ::;N. 

mm.).   The  gray  commissure  lies  -^    v  $ 

very    near    the    middle    of    the        X^     \k 

spinal  cord,  and  the  ventral  me-      Jpg  '    ,  ^ 

dian  fissure  is,  therefore,  quite  as      fi|$||j 
deep  as  the  dorsal  median  sep- 

tum-  <  ^'••^^"  - -' 

Both  the  ventral  and   dorsal  ••'..- 

gray  horns  are  long  and  thick.  •: 

Each    dorsal    horn    contains    a 
large   apical   area   of   gelatinous  ^^M^^  ^S^K^'-^ 

substance,  is  somewhat  lonsrer  on      ^ 

FIG.  521. — TRANSECTION  OF  THE  SPINAL 

its    lateral    than    on    its    medial         CORD  OF  A  CHILD,  EIGHTH  THORACIC 
side,  and  reaches  nearly  to  the         SEGMENT. 
dorsal  surface  of  the  spinal  cord,  Weigert  stain.     X  7. 

opposite  the  dorsolateral  sulcus. 

The  dorsal  nerve  roots  entering  at  this  level  are  apparently  directed 
toward  the  middle  of  the  tips  of  the  dorsal  horns  of  gray  matter;  once 
within  the  spinal  cord  they  pass  around  to  the  mesial  side  of  the  dorsal 
horns. 

The  ventral  horns,  somewhat  larger  than  the  dorsal,  present  two 
short  and  broad  protuberances,  the  one  at  the  ventromesial,  and  the 
other  and  more  prominent  at  the  ventrolateral  angle.  A  similar  though 
less  prominent  protuberance  is  seen  at  the  base  of  the  ventral  horn, 
on  its  lateral  aspect.  Each  of  these  projections  contains  a  more  or 
less  well-defined  group  of  motor  nerve  cells.  The  cell  groups  of  the 
ventral  horns  in  the  lumbar  region  are  therefore  a  ventromedial,  ventro- 
lateral, and  dorsolateral,  together  with  an  ill-defined  central  group  oc- 
cupying the  deeper  'intermediate  zone'  of  gray  matter. 

The  nerve  centers  contained  in  the  lumbar  region  control  the  re- 
flexes and  musculature  of  the  lower  limbs  and  the  lower  part  of  the 
abdominal  wall. 

A  transection  of  the  spinal  cord  in  the  thoracic  region  is  of  small 


602  THE  NEEVOUS  SYSTEM 

diameter  (eight  millimeters),  and  is  very  nearly  circular  in  outline. 
The  white  matter,  since  it  contains  the  many  nerve  fibers  going  to  and 
coming  from  the  lumbar  enlargement,  is  much  more  voluminous  than 
the  gray  matter.  The  latter  is  reduced  to  a  comparatively  small  central 
mass. 

The  dorsomedial  column  attains  a  considerable  size  in  this  region, 
and  is  distinctly  marked  off  from  the  adjacent  dorsolateral  column  by 
a  fibrous  septum  derived  in  part  from  the  pia  mater,  in  part  being 
of  neuroglia  composition.  The  dorsal  and  the  lateral  columns,  having 
been  much  augmented  by  the  influx  of  fibers  from  the  large  dorsal 
roots  of  the  lumbar  nerves,  form  the  larger  part  of  the  white  matter. 
The  gray  matter  consequently  appears  to  be  pushed  forward,  its  gray 
commissure  lies  considerably  ventrad  of  the  center  of  the  spinal  cord, 
the  ventral  median  fissure  is  shorter  than  the  dorsal  median  septum,  and 
the  tips  of  the  dorsal  gray  horns  are  far  removed  from  the  surface, 
being  only  connected  with  the  dorsolateral  sulcus  by  the  slender  dorsal 
nerve  roots.  In  fact,  the  dorsal  horns  of  gray  matter  in  this  region 
are  reduced  to  a  minimum  size;  they  are  short  and  slender  and  contain 
comparatively  few  nerve  cells. 

At  the  base  of  each  dorsal  horn,  on  its  mesial  side,  there  is  a  dis- 
tinctly outlined  cell  group  whose  transection  is  of  oval  or  circular  out- 
line. Indeed,  this  cell  group,  the  cell  column  of  Clarke,  begins  in  the 
second  or  third  lumbar  segment,  and  is  continued  upward  to  the  second 
or  third  thoracic — at  times  even  into  the  lowermost  cervical  segments 
— at  which  level  it  has  dwindled  to  a  relatively  insignificant  group.  In 
the  lower  lumbar  region  an  ill-defined  group  of  cells  occupying  a  similar 
position  and  having  the  same  function  is  known  as  the  nucleus  of 
Stilling. 

The  ventral  gray  horns  are  very  short  and  narrow,  and  their  cells 
cannot  be  subdivided  into  groups  as  in  the  other  regions  of  the  spinal 
cord.  In  the  upper  part  of  the  thoracic  region  a  distinct  protuberance 
makes  its  appearance  at  the  base  of  the  ventral  horn,  on  its  lateral 
aspect.  This  is  the  precursor  of  the  larger  lateral  horn  of  the  cervical 
region.  In  the  upper  thoracic  region  it  contains  a  small  cell  group,  the 
dorsolateral. 

The  nerve  centers  of  the  thoracic  segments  control  the  upper  abdom- 
inal region,  the  thorax,  and  the  viscera. 

In  the  lower  half  of  the  cervical  region  the  spinal  cord  presents 
a  distinct  enlargement,  within  the  gray  matter  of  which  are  the  nuclei 
for  the  upper  limbs.  The  spinal  cord  in  this  region  is  somewhat  flat- 


THE  SPINAL  COED  603 

tened,  its  transverse  diameter  (14  mm.)  considerably  exceeding  its 
anteroposterior.  The  major  portion  of  the  white  matter  is  still  con- 
tained within  its  dorsal  rather  than  its  ventral  portion,  the  gray  com- 
missure appearing  to  lie  somewhat  ventrad  of  the  center.  The  dorsal 
median  septum  dips  inward  for  a  much  greater  distance  than  does  the 
ventral  median  fissure. 

The  dorsal  columns  are  decidedly  larger  than  the  ventral,  and  a 
distinct  groove,  the  paramedial  sulcus,  from  which  a  fibrous  septum 
is  continued  inward,  separates  the  dorsomedial  from  the  dorsolateral 
column. 

The  dorsal  gray  horns  are  long,  relatively  slender,  and  more  divergent 
than  in  the  lower  levels.  They  do  not  reach  the  surface  of  the  spinal 
cord,  but  are  connected  therewith  by  the  long,  slender  dorsal  nerve 
roots.  The  gray  matter  of  the  dorsal  horns  in  this  region  is  more  or 
less  invaded  by  bundles  of  nerve  fibers  derived  from  the  lateral  and 
dorsal  columns;  the  tips  of  the  dorsal  horns  are  thus  almost  cut  oC 
from  the  deeper  portions  of  gray  matter. 

The  ventral  horns  are  both  long  and  broad.  They  present  three 
noticeable  promontories  or  processes — a  medial  (ventromedial),  a  ventral 
(ventrolateral),  and  a  lateral.  The  lateral,  because  of  its  special  promi- 
nence, is  frequently  called  the  lateral  horn;  it  is  one  of  the  noticeable 
characteristics  of  the  cervical  region. 

Each  of  these  processes  contains  a  corresponding  cell  group;  hence 
we  distinguish  in  the  cervical  enlargement  a  mesial,  a  ventral,  and  a 
lateral  group,  together  with  a  small  intermediolateral,  which  is  partially 
or  completely  detached  from  the  dorsal  portion  of  the  lateral  group. 
There  is  also  a  small  disseminated  central  group  of  nerve  cells  occupying 
the  deeper  portion  of  the  ventral  horn. 

The  nuclei  of  the  segments  included  in  the  cervical  enlargement 
contain  the  centers  for  the  musculature  and  sensory  reflexes  of  the  upper 
limbs.  The  partial  control  of  the  pupillary  movements  in  the  eye  is 
also  located  in  the  lowermost  segments  of  this  region. 

In  the  upper  half  of  the  cervical  region  a  transection  of  the  spinal 
cord,  except  for  its  larger  size,  resembles  very  closely  that  of  the  thoracic 
region.  The  larger  size  is  due  to  an  increase  in  the  white  matter  of 
the  dorsal  and  lateral  columns,  consequent  upon  the  acquisition  of 
new  fibers  which  enter  the  subjacent  segments  from  the  nerves  sup- 
plying the  upper  extremities,  together  with  an  increased  number  of 
centrifugal  fibers  from  the  cerebrum  which  are  distributed  to  the  gray 
matter  of  this  region. 


604 


THE  NERVOUS  SYSTEM 


The  ventral  columns  are  also  much  increased  in  size  by  the  addi- 
tion of  many  fibers  coming  down  from  the  medulla  and  cerebellum, 
which  place  the  nerve  centers  of  the  spinal  cord  in  close  relation  with 
those  of  the  cranial  nerves  and  with  the  association  centers  of  the  cere- 
bellum. 

In  addition  to  the  large  size  of  its  white  columns,  a  noticeable  char- 
acteristic of  the  upper  cervical  region  is  the  prominence  of  its  lateral 

horns  of  gray  matter. 
Just  dorsal  to  the 
lateral  horns  is  also  a 
peculiar  reticular  for- 
mation which  results 
from  an  invasion  of 
the  adjacent  portions 
of  the  lateral  white 
columns  by  bands  of 
gray  matter.  The 
gray  matter  thus 
forms  a  coarse  net- 
work whose  meshes 
inclose  isolated  bun- 
dles of  longitudinal 
nerve  fibers. 

The   ventral  horn 

cells  of  this  region  are  scarcely  divisible  into  groups,  but  a  large  and 
distinct  cell  group,  the  intermediolateral  cell  column,  occupies  the 
so-called  lateral  horn. 

The  nuclei  of  the  upper  cervical  region  innervate  the  skin  and 
muscles  of  the  neck  and  shoulder,  they  also  supply  the  diaphragm.  The 
nerve  cells  of  this  region  not  only  supply  the  cervical  spinal  nerves,  but 
they  also  send  root  bundles  to  the  spinal  accessory  or  eleventh  cerebral 
nerve. 


FIG.  522. — TRANSECTION  OF  THE  SPINAL  CORD  OF  A 
CHILD,  FOURTH  CERVICAL  SEGMENT. 

Weigert  stain.     X  7. 


THE  CEREBELLUM 


The  cerebellum  consists  of  an  irregular  core  of  white  substance, 
the  medulla,  and  a  thick  mantle  of  gray  matter,  the  cortex.  It  com- 
prises two  hemispheres  or  lobes  connected  by  a  third  lobe,  the  vermis. 
Each  lobe  is  a  combination  of  lobules  which  include  a  variable  number 
of  transverse  convolutions  or  folia.  Bach  folium  contains  a  medullary 


606 


THE  NERVOUS  SYSTEM 


core  and  is  covered  by  a  cortical  layer.     The  central  medulla  contains 
four  paired  masses  of  gray  substance,  the  internal  nuclei. 

THE  CEREBELLAR  CORTEX 

The  cortex  is  divisible  into  an  inner  granular  layer,  and  an  outer 
molecular  layer.  The  granular  layer  in  a  fresh  section  appears  rust- 
colored;  in  a  stained  preparation  it  appears  much  darker  and  more 
granular  than  the  molecular  layer  due  to  the  abundance  of  nuclei;  it 
is  thickest  over  the  summit  of  the  folium,  and  thinnest  in  the  depth 
of  the  sulcus  between  adjacent  folia. 


FIG.  524. — FROM  A  SECTION  OF  THE  CEREBELLAR  CORTEX  OF  MAN. 

a-a,  pia  mater;  b-b,  molecular  layer;  c-c,  granular  layer;  d-d,  white  matter  of 
the  medulla.     Nissl's  stain.     Photo.     X  38. 


THE  CEREBELLUM  607 

The  most  conspicuous  and  distinctive  elements  of  the  cerebellar 
cortex  are  the  Purkinje  cells,  situated  along  a  line  marking  the  division 
between  molecular  and  granular  layers.  They  are  regarded  as  belong- 
ing to  the  molecular  layer.  The  remaining  cellular  elements  of  the 
cortex  cannot  be  studied  in  detail  in  ordinary  histologic  preparations. 
They  must  be  identified  mainly  by  their  relative  size  and  position.  Our 


FIG.  525. — A  PURKINJE  CELL  FROM  THE  HUMAN  CEREBELLAR  CORTEX. 
Moderately  magnified;     Photo.     (After  Berkley.) 

knowledge  of  their  finer  structure  and  their  interrelationships  has 
been  gained  by  use  of  special  staining  technics,  chiefly  the  Golgi  process. 
By  use  of  this  technic  two  other  types  of  cells  can  be  distinguished 
in  the  molecular  layer:  the  small  cortical  cells,  and  the  large  cortical 
or  basket-cells. 

The  Purkinje  cells  are  large  flask-shaped  elements,  with  typically 
a  robust  dendron  and  a  delicate  axon  at  opposite  poles.  The  axon 
passes  centrally  to  contribute  to  the  white  matter  of  the  medulla.  It 
gives  off  numerous  collaterals,  some  of  which  turn  back  into  the  molec- 
ular layer  and  terminate  in  relation  with  neighboring  cells  of  Purkinje. 
The  dendrou  passes  toward  the  surface  dividing  almost  immediately 


608 


THE  NERVOUS  SYSTEM 


into  two  coarse  branches,  which  each  divides  dichotomously  into  a  suc- 
cession of  increasingly  more  delicate  branches  forming  peripherally  a 
dendronic  field  of  extreme  profusion  of  non-anastomosing  fibrils.     The 
>       dendron  viewed  as  a  whole  constitutes  a  fan- 
JK  S  \     slinpcd    stniHure.      Its    expansion    is    in    a 

^^^^^^^  \s^    plane  at  right  angles  to  the  long  axis  of  the 
>,    :;      ffijr  convolution.     In  sections  parallel  with  the 

/  long  axis  of  the  convolution  the  dendronic 

field  is  very  narrow,  and  never  wider  than 
the  diameter  of  the  cell-body. 

The  basket-cells,  or  large  cortical  cells, 
are  multipolar  elements  with  relatively 
short  robust  branching  dendrons,  and  a 
long  axon  which  passes  horizontally  in  the 
same  plane  in  which  the  dendronic  expan- 
sion of  the  Purkinje  cells  are  placed.  Along 
its  course  it  gives  off  five  or  six  collaterals 
which,  as  also  the  post-collateral  portion 
of  the  axon  itself,  pass  centrally  toward  the 
Purkinje  cells  where  each  breaks  up  into  a 
profuse  terminal  arborization  which  invests 
the  cell-body  in  the  manner  of  a  'basket.' 
The  basket  cells  occupy  the  middle  and 
outer  portions  of  the  molecular  layer;  they 
are  apparently  of  the  nature  of  association 
neurons,  perbaps  coordinating  the  function 
of  a  number  of  Purkinje  cells. 

The  small  cortical  cells  are  distributed 
throughout  the  molecular  layer  but  are  more 
abundant  in  the  outer  half.  They  are  mul- 
tipolar and  vary  considerably  in  size,  some 
being  almost  as  large  as  the  basket  cells. 
They  possess  from  two  to  five  delicate  den- 
drons  distributed  for  the  most  part  in  the 
same  plane  as  those  of  the  Purkinje  cells. 
Their  short  slender  axon,  which  is  horizon- 
tally placed,  is  frequently  characteristically 
looped.  The  axon  of  some  of  these  cells  has  numerous  collat- 
erals. 

The  nuclear  or  granular  layer  also  contains  three  distinct  types 


FIG.  526. — A  PURKINJE  CELL 
FROM  THE  CEREBELLAR 
CORTEX  OF  THE  RABBIT. 


Highly  magnified. 
Nissl.) 


(After 


THE  CEREBELLUM  609 

of  cells :  the  granule  cells,  the  large  stellate  cells  and  the  so-called  soli- 
tary cells.  The  latter  are  small  fusiform  elements,  but  of  their  signifi- 
cance and  relationships  little  is  definitely  known. 

The  GRANULE  CELLS  have  a  general  distribution  throughout  the 
granular  layer.  They  are  of  relatively  small  size,  multipolar,  and  pos- 
sess short  dendrons  (frequently  four)  which  end  in  claw-like  processes. 
These  latter  are  in  close  relationship  with  the  so-called  eosin  bodies, 
small  spheroidal  finely  granular  masses  having  a  special  affinity  for 
eosin.  The  eosin  bodies  are  believed  by  some  to  represent  synapses 
between  the  dendrites  of  the  granular  cells  and  the  telodendria  of  the 
centripetal  mossy  fibers  contributed  by  the  medulla.  The  axon  of  the 
granule  cell  is  unique  among  the  cerebellar  cortical  neurons  in  that  it 
passes  toward  the  surface;  here  it  divides  in  T-fashion,  the  branches 
passing  parallel  to  the  long  axis  of  the  convolutions  thus  coursing  at 
right  angles  to  the  dendronic  expansion  of  the  Purkinje  cells,  in  relation 
with  which  they  probably  end. 

The  LARGE  STELLATE  CELLS  have  a  limited  distribution  in  the  granu- 
lar layer;  they  are  more  or  less  closely  confined  to  the  boundary  zone 
between  the  molecular  and  granular  layers.  They  are  large  multipolar 
cells,  with  a  profuse  dendronic  contribution  to  the  molecular  layer, 
and  an  almost  equally  profuse  short  axonic  and  collateral  contribution 
to  the  granular  layer  where  the  telodendria  end  in  relation  to  the 
granule  cells.  These  are  typical  Golgi  cells  of  the  second  type. 


THE  MEDULLA 

The  medulla  next  the  cortex  contain  three  important  types  of  medul- 
lated  fibers :  the  climbing  fibers,  the  mossy  fibers,  and  the  axons  of  the 
Purkinje  cells.  The  latter  are  centrifugal  fibers  passing  to  the  internal 
nuclei.  The  climbing  fibers  are  so  designated  by  reason  of  their  end- 
ing in  profuse  telodendria  which  are  closely  associated  with  the  dendrons 
of  the  Purkinje  cells,  apparently  'climbing'  over  them.  The  mossy  fibers 
owe  their  designation  to  the  nodular  mossy  character  of  their  terminal 
branches  within  the  granular  layer.  Their  end-arborizations  are  in- 
timately related  to  those  of  the  dendrons  of  the  granule  cells  prob- 
ably contributing  to  the  formation  of  the  eosin  bodies. 

Both  cortex  and  medulla  contain  an  abundant  neurogliar  supporting 
substance.  The  astrocytes  of  the  cortex  are  largely  of  the  short-rayed 
(mossy)  type;  those  of  the  medulla  are  exclusively  of  the  long-rayed 


Basket 
cell 


Axon  Telodendrion 

Large  of  cell  of  of  collateral 

stellate  granular  climbing 

cell         layer  fiber 


610 


THE  CEREBRAL  CORTEX  611 

type.    Next  the  surface  of  the  cortex  the  neuroglia  tissue  is  condensed, 
forming  a  thick  peripheral  velum. 

The  foregoing  is  summarized  in  the  following  outline: 

{Hemispheres 
Vermis 
Cerebellum  J  Lobules 

[Folia 
I.  Cortex. 

A.  Molecular  layer. 

1.  small  cortical  cells. 

2.  basket  cells — small  stellate  cells — large  cortical  cells. 

3.  Purkinje  cells. 

B.  Nuclear  or  Granular  layer. 

1.  granule  cells,  with  dendritic  arborizations  ending  in 

close  association  with  eosin  bodies. 

2.  large  stellate  cells. 

3.  solitary  cells. 

II.  Medulla — medullated  nerve  fibers. 

(a)  axon  of  Purkinje  cells. 

(b)  mossy  fibers,  ending  in  eosin  bodies  of  granular 

layer. 

(c)  climbing  fibers. 


THE   CEREBRAL   CORTEX 

The  cerebrum  consists  of  two  large  symmetrically  paired  lobes  or 
hemispheres  connected  by  a  bridge  of  white  matter,  the  corpus  callosum. 
Each  hemisphere  includes  essentially  a  central  mass  of  white  substance 
or  medulla,  containing  the  internal  nuclei  or  basal  ganglia — paired 
masses  of  gray  matter — and  a  covering  of  gray  substance,  the  cortex  or 
pallium.  The  cortex  is  greatly  folded,  thus  becoming  marked  by  con- 
volutions or  gyri  with  intervening  fissures  or  sulci.  The  surface  of  each 
hemisphere  may  be  divided  into  four  principal  lobes:  (1)  the  frontal 
lobe,  bounded  posteriorly  by  the  fissures  of  Eolando  and  Sylvius;  (2) 
the  parietal  lobe,  extending  from  the  fissure  of  Rolando  in  front  to  the 
parieto-occipital  fissure  behind  and  the  Sylvian  fissure  below;  (3)  the 
occipital  lobe,  bounded  anteriorly  by  the  parie+o-occipital  sulcus;  and 


612 


THE    NERVOUS   SYSTEM 


(4)  the  temporal  lobe,  lying  below  the  fissure  of  Sylvius.  The  cortical 
portion  folded  under  the  lips  of  the  Sylvian  fissure  is  known  as  the 
insula  (lobulus  insula).  The  average  thickness  of  the  cortex  is  about 
three  millimeters,  but  in  the  motor  area  of  the  frontal  lobe,  it  may  attain 
a  depth  of  five  millimeters,  while  in  the  occipital  lobe  it  may  become 
reduced  to  almost  two  millimeters. 

Fissure  of  Rolando 
Parietal  lobe 
Parieto-occipital 


FIG.  528. — LEFT  LATERAL  SURFACE  VIEW  OF  CEREBRAL  CORTEX  IN  MAN,  SHOW- 
ING THE  LOBES,  MAIN  SULCI,  AND  THE  LARGER  FUNCTIONAL  AREAS. 
Later  researches  have  shown  that  the  motor  area  is  located  entirely  in  the  pre- 
Rolandic  region.     (After  Oppenheim.) 

The  nerve  cells  which  enter  into  the  formation  of  the  gray  matter 
of  the  cerebral  cortex  present  a  remarkable  tendency  to  arrange  them- 
selves in  more  or  less  well-defined  layers  parallel  to  the  surface  of  the 
cerebral  convolutions.  The  number  and  arrangement  of  these  layers 
in  the  various  lobes  varies,  however,  with  the  peculiar  function  of  each 
of  these  areas.  Thus,  in  the  motor  area  there  is  a  five  layer  type,  in 
the  parietal  lobe  a  seven  layer  type,  in  the  occipital  lobe  a  six  or  eight 
layer  type.  The  histologically  different  areas  shade  into  each  other  by 
insensible  gradations. 

In  general,  it  may  be  assumed  that  the  nerve  cells  of  all  of  these 
layers  are  included  in  one  or  two  physiologically  distinct  groups  or 


THE  CEREBRAL  CORTEX 


613 


types:  those  whose  axons  enter  the  projection  paths,  and  those  whose 
axons  enter  the  association  paths ;  also  that  while  these  cells  intermingle 
with  each  other  in  all  portions  of  the  cortex,  yet  certain  areas 'are  char- 
acterized by  an  undue  proportion  of  one  or  the  other  type,  and  may 
accordingly  be  considered  as 
either  projection  centers  or  as- 
sociation centers. 

The  larger  cells  belong,  as 
a  rule,  to  the  projection  centers, 
and  the  peculiar  type  of  large 
cell  contained  in  a  given  center 
may  often  be  considered  as 
characteristic  of  that  particular 
area.  Thus  the  motor  area  con- 
tains giant  pyramidal  cells 
(Betz  cells),  and  the  visual  area 
the  giant  'solitary  cells'  of 
Meynert. 

The  larger  cells,  being  of 
Golgi's  Type  I,  are  assumed  to 
be  connected  with  the  projec- 
tion fibers.  On  the  other  hand, 
the  smaller  cells — granule  cells, 
polymorphous  cells,  etc. — which 
more  frequently  belong  to 
Golgi's  Type  II,  are  thought  to 
supply  the  axons  of  association 

paths.       Those     large    areas-         (After  w    yon   Bechterew }     (Barker> 
parietal     lobe,     frontal     lobe, 
lobulus    insulse — which    consist 

in  so  large  a  part  of  the  smaller  type  of  cells,  may  therefore  be  supposed 
to  contain  the  larger  association  centers. 

The  cells  in  any  given  portion  of  the  cortex  are  not  only  arranged  in 
layers  parallel  to  the  surface  of  the  cerebral  convolutions,  but  the 
passage  of  fibers  of  the  medulla  to  or  from  their  terminations  within 
the  pallium,  also  separates  the  cells  of  the  cortex  into  irregular  rows 
or  striations,  whose  axis  is  perpendicular  to  the  surface  of  the  con- 
volutions. 


Fro.  529. — LARGE  PYRAMIDAL  CELL  OF  THE 
CORTEX. 

(After    W.    von    Bechterew.) 
"The  Nervous  System.") 


FIG.  530. — SCHEME  OF  THE  MOTOR  AREA  OF  THE  CEREBRAL  CORTEX,  SHOWING  THE 
EFFECT  OF  VARIOUS  STAINING  METHODS. 

1,  Golgi's  stain;  2,  Weigert's  stain;  3,  hematein  and  eosin;  4,  relative  depth  of 
each  layer.  A,  association  neurons;  Ag,  angular  cells  of  the  polymorphous  layer; 
As  F,  association  fibers;  Ax,  axons;  C,  collateral;  C  F,  centripetal  fibers;  E,  terminal 
fibers;  F,  fusiform  cell  of  the  polymorphous  layer;  G,  Golgi  cells,  Type  II;  M,  cells 
of  Martinotti;  P  C,  collateral  of  a  pyramidal  cell;  Py,  pyramidal  cells;  Py  ax,  axen 
of  a  pyramidal  cell;  Py  S,  pyramidal  axons  passing  to  the  cerebral  medulla.  (After 
Berkley.) 

614 


THE   MOTOR   AREA 


615 


THE  MOTOR  AREA 

In  the  motor  area,  including  the  pre-Bolandic  or  pre-central  gyrus 
and  a  posterior  portion  of  the  frontal  lobe,  the  cortical  cells  form  five 
tangential  layers,  as  follows: 

1.  Molecular  layer.  

2.  Outer  polymorphous  cell  layer. 

3.  Small  pyramidal  cell  layer. 

4.  Large  pyramidal  cell  layer. 

5.  Inner  polymorphous  cell  layer. 
The    MOLECULAR    LAYER     (stratum 

zonale)  consists  of  a  net  work  of  fine 
dendronic. fibers,  derived  from  the  deeper 
layers,  which  are  disposed  in  tangential 
meshes  beneath  the  pia  mater.  Occa- 
sionally small  cells,  apparently  displaced 
from  the  deeper  cell  layers,  are  scat- 
tered among  these  fibers;  they  are  of 
polymorphous  form,  and  their  processes 
are  confined  to  the  molecular  layer.  The 
surface  of  the  molecular  layer  is  cov- 
ered by  a  marginal  velum  of  neuroglia 
homologous  with  that  beneath  the  pia 
mater  of  the  spinal  cord. 

The  SECOND,  or  OUTER  POLYMOR- 
PHOUS, CELL  LAYER,  is  a  thin  stratum. 
Its  cells  are  frequently  clumped,  thus 
forming  groups  of  various  size.  This 
grouping  is,  however,  more  distinct  in 
some  other  regions,  e.g.,  the  olfactory 
area,  than  in  the  motor  area  itself. 

The  THIRD  LAYER,  SMALL  PYRAMIDAL 

CELLS,    is   somewhat   thicker   than   the 

above.     It  consists  of  numerous  small 

cells — triangular,    pyramidal,    or    pyri- 

form  in  shape — whose  pointed  apices  are 

directed  toward  the  surface.    Three  sets 

of  dendrons  are  given  off  by  these  cells,  an  apical  process  which  passes 

outward  to  ramify  in  the  outer  molecular  layer,  and  from  either  side. 


GLP.P 


PoLP. 


FIG.  531. — DISPOSITION  OF  THE 
NERVE  FIBERS  IN  THE  CERE- 
BRAL CORTEX  OF  MAN. 

Between  the  vertical  bands  of 
radial  fibers  are  the  areas  of  inter- 
radial  fellwork.  The  supraradial 
feltwork  includes  the  tangential 
fiber  layer  or  stratum  zonale  (M. 
P.),  and  the  stripe  of  Bechterew 
(Subm.P.).  c.z.,  subpial  neurogliar 
layer;  Gt.P.P.,  outer  stripe  of  Bail- 
larger;  Pol.P.,  inner  stripe  of  Bail- 
larger;  W.,  white  matter.  (From 
Barker,  after  L.  Andriezen.) 


616 


THE  NERVOUS  SYSTEM 


of  the  base  of  the  cell  a  second  set,  whose  processes  are  distributed  in 
a  plane  nearly  corresponding  to  that  in  which  their  cell  bodies  lie.     The 
<-•-         — — ^  axon  is  usually  given  off  from  the  basal  surface 

of  the  cell,  and  passes  from  this  point  directly 
inward  to  the  white  matter  of  the  cerebral 
medulla. 

The  FOURTH  LAYER,  that  of  the  LARGE 
PYRAMIDAL  CELLS,  is  also  a  thick  layer.  Its 
cells  are  of  the  same  shape,  and  distribute  their 
processes  after  the  same  manner  as  those  of 
the  small  pyramidal  cell  layer.  The  motor 
area  is  specially  characterized  by  the  large  size 
of  the  cells  of  this  layer.  The  largest  of  these, 
the  Cells  of  Betz,  are  about  six  times  as  large 
as  the  small  pyramidal  cells,  which  have 
a  fairly  uniform  size  of  about  ten  mi- 
crons. 

The  FIFTH,  or  INNER  POLYMORPHOUS  CELL, 
LAYER,  is  thicker  than  the  preceding.  Its  cells 
are  of  very  varied  form — pyramidal,  stellate, 
fusiform,  and  granule  cells — and  are  less 
densely  packed  than  is  the  case  in  the  more 
superficial  layers.  They  are  intermediate  in 
size,  between  the  cells  of  the  second  and  the 
third  layers.  The  axons  of  the  inner  polymor- 
phic cells,  in  large  part,  pass  to  the  white 
matter  of  the  medulla,  though  some  of  them  are 
distributed  laterally  to  neighboring  convolu- 
tions. Their  dendrons  are  partially  distrib- 
uted within  the  layer  in  which  they  arise,  but 
by  far  the  larger  portion  pass  to  the  more  su- 
perficial pyramidal  cell  layers.  Many  of 
the  nerve  cells  of  this  layer,  e.g.,  the  granule 
cells,  are  very  small,  their  nucleus  being 
covered  with  an  extremely  narrow  shell  of 
cytoplasm. 

It  is  noticeable  that,  as  a  rule,  the  dendronic  processes  from  the 
cells  of  all  five  layers  are  distributed  either  in  the  same  plane  as  their 
cell  bodies,  or  they  pass  toward  the  surface,  where  many  of  them  enter 
the  superficial  molecular  layer.  The  axons,  on  the  other  hand,  are  di- 


FIG.  532. — HUMAN  COR- 
TEX CEREBRI,  MOTOR 
AREA. 

a,  tangential  fiber  kyer; 
b,  outer  polymorphous 
cells;  c,  small  pyramidal 
cells;  d,  large  pyramidal 
cells;  e,  inner  polymor- 
phous cells.  Nissl's  stain. 
Moderately  magnified. 
(After  Schlapp.) 


THE  SENSOEY  AREA 


617 


rected  inward  toward  the  white  matter  of  the  cerebral  medulla,  in 
which  they  pass,  either  as  association  or  as  projection  fibers,  to  many 
very  distant  parts.  Notable  exceptions  to  this  latter  rule,  however,  are 
the  so-called  cells  of  Martinotti,  which  occur  to  some  extent  in  all 
layers,  but  which,  though  found  in  the  pyram- 
idal layers,  are  especially  numerous  among 
the  polymorphous  and  granule  cells.  They  are 
small  polymorphic  cells,  which  send  their  axons 
to  the  superficial  molecular  layer,  giving  off 
collaterals  on  their  way. 

The  cell  types  in  other  portions  of  the  cor- 
tex correspond  very  closely  to  those  of  the 
motor  area.  There  are,  however,  slight  but 
characteristic  variations  which  are  worthy  of 
notice. 

The  cortex  of  the  parietal  lobe  (also  of 
the  frontal,  temporal,  convex  surface  of  the 
occipital  lobes,  and  the  insula] — sensory  area 
— presents  a  seven  layer  type,  the  additional 
layers  resulting  from  an  aggregation  of  the 
granule  cells  into  one  plane,  which  thus  di- 
vides the  large  pyramidal  cell  layer.  This 
type,  therefore,  presents  the  following  layers : 

1.  Molecular  or  tangential  fiber  layer. 

2.  Outer  polymorphous  cell  layer. 

3.  Small  pyramidal  cell  layer. 

4.  Outer  large  pyramidal  cell  layer. 

5.  Granule  cell  layer. 

6.  Inner  large  pyramidal  cell  layer. 

7.  Inner  polymorphous  cell  layer. 

The  distribution  of  this  cortical  type  is 
suggestive  of  a  close  relation  to  the  great  asso- 
ciation centers.  Moreover,  its  most  noticeable 
characteristics  are  the  abundance  of  its  granule 
cells  and  the  relative  paucity  of  pyramidal  cells, 
especially  those  of  the  giant  pyknomorphic 
variety. 

In  the  visual  area— median  surface  of  the  occipital  lobe— the  for- 
mation is  described  as  either  a  six  or  an  eight  layer  type.    The  pyram- 
idal cell  layers  are  reduced  to  extreme  thinness,  the  giant  pyramids 
39 


FIG.  533.— HUMAN  COR- 
TEX CEREBRI,  PARIE- 
TAL LOBE. 

a,  tangential  fiber  layer; 
6,  outer  polymorphous 
cells;  c,  small  pyramidal 
cells;  d,  outer  large  pyr- 
amidal cells;  e,  granule 
cells;/,  inner  large  pyram- 
idal cells;  g,  inner  poly- 
morphous cells;  h,  white 
matter  of  the  medulla. 
Nissl's  stain.  Moderately 
magnified.  (AfterSchlapp.) 


618  THE    NERVOUS    SYSTEM 

being  noticeably  deficient.  The  stripes  of  Baillarger,  thin  layers  of 
tangential  fibers  on  the  deeper  portions  of  the  cortex,  are  especially 
distinct.  So  many  granule  cells  are  scattered  among  those  of  the  pyram- 
idal type  that  it  becomes  scarcely  possible  to  distinguish  from  one  another 
the  second,  third,  and  fourth  layers.  When  these  three  layers  are  in- 
dividually considered,  the  type  presents  eight  layers;  if,  however,  they 
are  collectively  considered  as  one  stratum,  the  type  presents  six  layers. 
With  this  reservation,  the  following  layers  may  be  distinguished: 

1.  Molecular  or  tangential  fiber  layer. 

2.  Outer  polymorphous  cell  layer. 

3.  Small  pyramidal  cell  layer. 

4.  The  layer  of  granule  and  large  pyramidal  cells. 

5.  The  outer  stripe  of  Baillarger  (great  pyramidal  plexus). 

6.  The  granule  cell  layer. 

7.  The  inner  stripe  of  Baillarger  (polymorphous  plexus). 

8.  Inner  polymorphous  cell  layer. 

The  special  characteristics  of  the  visual  area  are  the  abundance  of  tan- 
gential fibers,  as  evidenced  by  the  prominent  stripes  of  Baillarger,  the 
thick  fiber  layer  in  the  deeper  part  of  the  molecular  stratum,  the  abun- 
dance of  granule  cells,  the  paucity  and  irregular  form  of  the  pyramidal 
cells,  and  finally  the  presence  in  the  inner  stripe  of  Baillarger  and  in  the 
outer  portion  of  the  deep  polymorphous  cell  layer  of  numerous  large 
isolated  multipolar  cells,  the  giant  'solitary  cells'  of  Meynert.  The  outer 
stripe  of  Baillarger  is  especially  prominent  in  the  visual  area  (area 
striata)  and  is  here  known  as  the  stripe  of  Gennari. 

In  the  auditory  area — temporal  lobe — the  seven  layer  type  is  found. 
The  structure  in  this  area  is  apparently  identical  with  that  previously 
described  for  the  seven  layer  type  in  the  parietal  lobe. 

In  the  olfactory  area  — hippocampal  gyrus — the  cells  of  the  outer 
polymorphous  layer  arrange  themselves  in  groups,  and  the  pyramidal 
cells  become  largely  transformed  into  polymorphic  and  fusiform  cells; 
these  lie  between  the  characteristic  outer  layer  and  the  inner  layer  of 
polymorphic  cells,  giving  to  the  cortex  of  this  region  a  three  layered 
structure  of  indistinct  outlines. 

FIBEK  TRACTS. — The  corticifugal  axons  of  the  cells  of  the  several 
layers  are  collected  below  the  upper  level  of  the  large  pyramidal  cell 
layer  into  vertical  columns  which  pass  to  the  medulla  as  the  bands  of 
radial  fibers.  In  these  same  columns  course  also  the  corticipetal  axons. 
The  cortex  thus  becomes  divided  vertically  into  cell  rays  and  fiber 


THE  FIBER  TRACTS 


619 


rays,  as  was  mentioned  above.  Between  the  fiber  columns  the  dendronic 
network  is  known  as  the  interradial  felt  work;  peripheral  to  where  the 

fiber  rays  begin,  this  dendronic  network — _^o 

forms  the  supraradial  feltwork.    At  about    ti|  \ 

the  middle  of  the  large  pyramidal  cell    I  ,'**** 
layer,  abundant  horizontal  dendrons  pro-    't/^; 
duce   a   distinct  broad   band,   the   outer    / 
stripe  of  Baillarger.     Between  the  large    | 
pyramidal  cell  layer  and  the  outer  poly-      •#./;'' 
morphic  cell  layer,  a  similar  but  narrower 
band  is  known  as  the  inner  stripe  of  Bail-     \  ..VV,;'.', ,  ,•;' 
larger.      These    stripes    are    most    pro- 
nounced in  the  visual  areas  as  was  said 
above.     Another  band  of  similar  nature 
at   about   the  outer   limit  of  the   small 
pyramidal  cell  layer  forms  the  stripe  of 
Bechterew.     Beneath  the  peripheral  neu- 
rogliar  marginal  velum  the  dendrons  of 
the  pyramidal  cells  branch  and  form  thus 
a  band  of  horizontal  fibers,  the  tangen- 
tial fiber  layer  or  molecular  fiber  layer. 
These  fiber  bands  are  conspicuous  only  in 
specimens    prepared    with    the    Weigert 
technic.     Both  cortex  and  medulla  con- 
tain   abundant    neuroglia    cells.      Those 
contributing    almost    exclusively    to    the 
marginal   velum   are   fusiform   elements 
with    lateral    tufts    of    short    horizontal 

fibers,  and  an  expanding  tuft  of  delicate  fibers  passing  to  the  inner 
border  of  the  small  pyramidal  cell  layer.  The  neurogliar  elements  of 
the  medulla  are  mostly  of  the  long-rayed  type. 


FIG.  534. — HUMAN  CORTEX  CER- 
EBRI,   OLFACTORY  REGION. 

a,  tangential  fiber  layer;  6, 
white  matter  of  the  medulla. 
Nissl's  stain.  Moderately  mag- 
nified. (After  Schlapp.) 


THE  MENINGES  AND  BLOOD  SUPPLY 


The  brain  and  spinal  cord  are  enveloped  by  the  meninges,  which 
include  three  fairly  distinct  membranes,  the  dura  mater,  arachnoid,  and 
pia  mater,  and  two  cavities  filled  with  lymph  or  a  lymph-like  fluid; 
by  this  arrangement  the  cerebrospinal  axis  is,  as  it  were,  sruspended 
in  fluid,  and  is  everywhere  surrounded  by  a  watery  cushion. 


620  THE  NEKVOUS  SYSTEM 

The  dura  mater  is  the  outermost  of  the  three  coats.  Within  the 
cranial  cavity  it  is  firmly  attached  to  the  bony  walls,  and  serves  as 
a  periosteum  for  the  internal  surface  of  the  bones  which  form  the  cranial 
cavity.  Within  the  vertebral  cavity  the  dura  mater  is  distinct  from  the 
periosteum  of  the  vertebrae,  with  which  it  is  connected  by  loose  fibrous 
tissue  and  masses  of  fat,  which  inclose  large  lymph  spaces  or  chambers, 
lined  by  endothelium  and  collectively  forming  the  epidural  space. 

The  dura  mater  is  composed  of  interlacing  bundles  of  fibrous  tissue 
containing  few  elastic  fibers.  The  disposition  of  its  fiber  bundles  varies 
somewhat  in  its  different  portions.  In  its  spinal  portion,  most  of  the 
bundles  are  longitudinally  disposed,  comparatively  few  passing  circularly 
around  the  circumference  of  the  vertebral  canal;  within  the  cranial 
vault  the  bundles  cross  at  acute  angles;  in  the  fakes  and  in  the  ten- 
torium  cerebelli  they  are  radially  disposed. 

The  cranial  dura  consists  of  two  distinct  layers,  an  outer,  which  is 
very  vascular  and  serves  as  the  bony  periosteum,  and  an  inner,  which 
is  but  slightly  vascular  and  may  be  considered  as  the  dura  proper.  It 
is  the  inner  layer  only  which  is  prolonged  inward  to  form  the  falx 
oerebri  and  the  falx  and  tentorium  cerebelli.  The  venous  dural  sinuses 
of  the  cranium  occupy  clefts  in  the  dura  along  the  lines  of  attach- 
ment. 

Although  the  dura  mater  is  but  poorly  supplied  with  blood-vessels, 
it  is  relatively  rich  in  lymphatics,  which  open  into  the  subdural  and 
epidural  spaces  and  are  continuous  with  the  perivascular  and  perineural 
lymphatics  which  leave  the  cerebrospinal  cavities  in  company  with 
the  cerebral  and  spinal  nerves  and  the  larger  blood-vessels.  In  this 
way  the  lymphatics  of  the  dura  mater  and  its  adjacent  spaces  are  in 
communication  with  the  lymphatic  vessels  of  the  eye,  nose,  ear,  and 
cervical  lymph  nodes.  These  communications  are  of  special  importance 
as  indicating  the  path  followed  by  certain  pathological  processes  which 
involve  the  meninges. 

Where  the  outer  surface  of  the  dura  is  not  attached  to  the  surround- 
ing bone  or  connective  tissue,  it  is  covered  by  a  thin  endothelioid  coat, 
the  lining  endothelium  (mesenchymal  epithelium)  of  the  epidural  spaces. 
Its  inner  surface  is  lined  by  somewhat  thicker  endothelial  cells,  forming 
the  wall  of  the  subdural  space.  The  dura  contains  sympathetic  fibers 
for  its  blood-vessels,  and  also  naked  spinal  and  cerebral  sensory 
fibers. 

The  arachnoid  is  a  thin  membranous  sheet  which  is  suspended  be- 
tween the  dura  and  the  pia  mater.  It  is  composed  of  a  delicate  areolar 


THE  MENINGES  AND  BLOOD  SUPPLY 


621 


tissue  which  contains  relatively  few  elastic  fibers  but  is  said  to  contain 
neither  blood-vessels,  lymphatics  nor  nerves.  This  thin  fibrous  mem- 
brane is  covered  on  either  side  by  a  layer  of  endothelium;  that  upon 
its  outer  surface  consists  of  cells  of  considerable  thickness,  which  are 
derived  from  the  lining  membrane  of  the  inner  wall  of  the  subdural 
space;  the  cells  upon  its 
inner  surface  are  thinner 
and  are  derived  from 
the  walls  of  the  sub- 
arachnoid  space. 

Delicate      septa  -  like 

bands  pass  from  the  in-  f       -^  v  ^      ^  m,     Q 

ner  surface  of  the  arach- 
noid to  the  adjacent  por- 
tions of  the  pia  mater 
(Fig.  535).  These  proc- 
esses are  likewise  invest- 
ed by  the  endothelial 
lining  of  the  subarach- 
noid  space.  A  similar 
investment  clothes  the 
processes  of  the  ligamen- 
tum  denticulatum  of  the 
spinal  cord  which  at- 
taches the  pia  mater  spi- 
nalis  on  either  side  to  the 
adjacent  portions  of  the 

dura  mater.     Subarachnoid  trabeculse  support  the  nerve  fibers  of  the 
dorsal  roots. 

A  fibrous  septum  passing  from  the  arachnoid  to  the  pia  mater,  along 
a  line  opposite  the  dorsal  median  septum  of  the  spinal  cord,  forms  a 
fairly  definite  partition,  the  septum  posticum.  In  the  cervical  region  this 
if?  an  interrupted  septum,  but  in  the  thoracic  and  lumbar  regions  it 
becomes  more  or  less  complete. 

The  cranial  arachnoid,  in  the  vicinity  of  the  cranial  sinuses,  notably 
the  superior  longitudinal  sinus,  sends  outward  many  villus-like  projec- 
tions or  arachnoid  villi  (Pacchionian  bodies;  granulationes  arachnoidales) 
which  protrude  into  the  venous  sinuses  to  such  an  extent  as  often  to 
produce  corresponding  depressions  in  the  inner  surface  of  the  bones  of 
the  cranial  vault,  into  which  they  push,  carrying  before  them  a  much 


FIG.  535. — SECTION  OP  THE  SPINAL  CORD  AND  ITS 
MEMBRANES,  FROM  THE  UPPER  THORACIC  RE- 
GION. 

a,  dura  mater;  6,  arachnoid;  c,  septum  posticum; 
d,  e,  f,  subarachnoid  trabecuUe;  n,  nerve  fiber 
bundles;  g,  ligamentum  denticulatum;  I,  subarach- 
noid space.  (From  Schafer,  after  Key  and  Retzius.) 


622  THE  NERVOUS  SYSTEM 

attenuated  portion  of  the  dura  mater.  These  villi  are  similar  in  struc- 
ture to  the  membranous  portion  of  the  arachnoid.  They  are  said  to  be 
absent  at  birth,  small  and  inconspicuous  in  childhood,  and  to  increase  in 
size  and  number  as  age  advances. 

Fluid  injected  into  the  arachnoid  or  into  the  neighboring  portions 
of  the  subarachuoid  space  passes  readily  into  the  lymph  spaces  of  the 
dura  mater,  and  may  even  be  forced  into  the  venous  cavity  of  the  cranial 
sinuses.  While  fluid  thus  injected  may  follow  artificial  rather  than  nat- 
ural channels,  it  seems  quite  possible  that  the  cerebrospinal  fluid  may 
during  life  find  its  way  along  such  channels  into  the  venous  sinuses  to 
the  relief  of  excessive  intracranial  pressure. 

The  pia  mater  is  intimately  adherent  to  the  surface  of  the  brain 
and  spinal  cord.  It  follows  all  the  irregularities  of  their  surfaces  and 
sends  prolongations  into  all  their  sulci.  In  the  larger  fissures  these  in- 
vaginations  form  a  double  fold  of  pial  tissue;  in  the  smaller,  the  in- 
vaginated  portions  fuse  to  form  a  thin  •  septum-like  prolongation  of  the 
pia.  In  this  particular  the  pia  mater  differs  from  the  arachnoid,  which 
bridges  over  all  the  sulci  without  dipping  into  any  but  the  largest  fis- 
sures. It  differs  also  from  the  dura  mater  which,  with  the  exception  of 
the  falces  and  tentorium,  is  not  prolonged  into  any  of  the  fissures  or  sulci 
of  either  the  brain  or  the  spinal  cord. 

The  pia  mater  is  a  connective  tissue  membrane  and  is  divisible  into 
an  inner  and  an  outer  layer.  The  outer  layer  is  composed  of  coarse 
fibrous  bundles  the  most  of  which  in  the  pia  mater  of  the  spinal  cord  run 
longitudinally,  while  the  finer  fibers  of  the  thin  inner  layer  are  cir- 
cularly arranged. 

Between  the  two  layers  are  many  blood-vessels  and  lymphatics,  the 
pia  mater  being  typically  a  vascular  membrane.  The  larger  blood- 
vessels are  loosely  embedded  in  the  outer  surface  of  the  pia,  some  of 
them  projecting  into  or  even  lying  entirely  within  the  subarachnoid 
space.  The  outer  surface  of  the  pia  mater,  as  also  the  sheaths  of  the 
vessels  which  are  loosely  attached  to  its  surface,  is  covered  with  a  layer 
of  very  thin  endothelial  cells  derived  from  the  lining  membrane  of  the 
subarachnoid  space. 

The  inner  surface  of  the  pia  is  everywhere  firmly  adherent  to  the 
surface  of  the  brain  and  spinal  cord.  The  slender  trabeculas  and  septa- 
like  processes  which  extend  into  the  superficial  portions  of  these  organs, 
consist  of  connective  tissues  whose  fibrous  bands  are  continuous  with 
those  of  the  membranous  pia  mater.  In  the  spinal  cord  many  of  these 
fibrous  bundles  extend  inward  as  far  as  the  gray  matter,  meanwhile  be- 


THE  MENINGES  AND  BLOOD  SUPPLY  623 

coming  intimately  associated  with  neuroglia.  In  both  the  spinal  cord 
and  the  hrain  the  pial  septa  serve  for  the  support  of  numerous  blood- 
vessels and  perivascular  lymphatics  which  are  distributed  through  this 
connective  tissue  to  all  portions  of  the  brain  and  spinal  cord. 

Within  the  cranium,  reduplications  of  the  pia  mater,  carrying  be- 
tween their  folds  a  layer  of  arachnoidal  tissue  and  an  extensive  plexus 
of  small  blood-vessels,  push  their  way  into  the  cerebral  ventricles  to  form 
the  superior  and  inferior  telce  choroidece.  These  choroid  plexuses  are 
separated  from  the  ventricular  cavities  by  an  investment  of  cuboidal 
cells,  which  in  fetal  and  infantile  life  are  ciliated,  and  which  are  derived 
from  and  are  continuous  with  the  ependyma  cells  lining  the  walls  of  the 
ventricles.  Thus  the  blood-vessels  of  the  telae  choroidese,  in  the  strictest 
anatomical  sense,  lie  without  and  not  within  the  cavity  of  the  cerebral 
ventricles,  for  they  are  everywhere  separated  from  those  cavities  by  the 
ependyma  cells,  which,  ontogenetically  at  least,  form  a  portion  of  the 
wall  of  these  vesicles.  The  cerebrospinal  fluid  is  supposed  to  originate 
largely  by  process  of  filtration  from  the  blood-vessels  of  these  choroid 
plexuses. 

The  pia  mater  contains  mostly  sympathetic  fibers,  but  probably  also  a 
few  sensory  cerebrospinal  fibers. 

The  peculiar  arrangement  of  the  three  constituent  membranes  of  the 
meninges  leaves  three  distinct  spaces  or  connected  groups  of  spaces 
which  are  filled  with  fluid.  These  are  the  epidural,  subdural,  and  sub- 
anichnoidal  spaces. 

The  epidural  space  comprises  a  connected  series  of  lymph  cavi- 
ties, which  is  of  limited  extent  within  the  cranium,  but  of  broad  extent 
within  the  spinal  canal.  These  spaces  are  lined  by  endothelium  which 
is  at  many  points  continuous  with  the  perivascular  and  perineural  lym- 
phatics and  through  them  with  the  lymphatic  vessels  of  the  general 
systemic  circulation.  Obviously  the  epidural  spaces  serve  as  large 
lymphatic  vessels  and  their  cavities  are  consequently  filled  with 
lymph. 

The  subdural  space  has  a  complete  lining  of  rather  thick  endothe- 
lial  cells.  The  walls  of  this  cavity  are  formed  by  the  dura  on  the  outer, 
and  the  arachnoid  on  the  inner  side.  Its  cavity  is  occupied  by  lymph 
and  is  continuous  with  the  lymphatic  vessels  of  the  dura,  and  through 
them  with  the  epidural  spaces  and  systemic  lymphatics. 

This  space  is  penetrated  by  the  outgoing  cranial  and  spinal  nerves, 
which  receive  an  investment  from  all  three  of  the  meningeal  coats.  The 
three  layers  composing  this  investment  soon  lose  their  distinctive  charac- 


624  THE  NEEVOUS  SYSTEM 

teristics,  fuse  together,  and  blend  with  the  epineurium  of  the  nerve 
trunks. 

Fluid  injected  into  the  subdural  space  may  be  readily  forced  into 
the  lymphatics  of  these  epi-  and  perineural  sheaths  and  may  thus  travel 
to  parts  quite  remote  from  the  central  nervous  system. 

The  subarachnoid  space  within  the  cranium  is  of  limited  breadth, 
but  within  the  spinal  canal  it  is  much  broader  and  contains  not  only  the 
larger  blood-vessels  which  are  loosely  attached  to  the  surface  of  the 
pia,  but  also  the  many  spinal  nerve  roots  pass  downward  through  this 
space  toward  their  foramina  of  exit. 

The  subarachnoid  space  is  lined  by  a  thin  endothelial  layer,  its 
outer  wall  being  formed  by  the  arachnoid,  its  inner  by  the  outer  surface 
of  the  pia  mater;  its  cavity  is  filled  with  cerebrospinal  fluid,  which 
closely  resembles,  yet  differs  somewhat  in  chemical  composition  from  the 
lymph.  It  contains  a  few  lymphocytes,  estimated  at  five  per  cubic  milli- 
meter of  fluid.  This  space  is  in  communication  through  the  foramen 
of  Majendie,  an  opening  in  the  roof  of  the  fourth  ventricle,  with  the 
central  canal  of  the  spinal  cord  and  the  ventricular  cavities  of  the  brain. 
It  is  also  thought  to  communicate  with  the  cerebral  ventricles  at  several 
other  points. 

The  spinal  portion  of  the  subarachnoid  space  is  crossed  by  a  posterior 
median  septum,  the  septum  posticum,  laterally  by  the  ligamentum  den- 
ticulatum,  and  by  several  irregular  but  incomplete  septa  which,  like  the 
ligamentum  posticum,  connect  the  pia  mater  with  the  arachnoid. 

The  ligamentum  denticulatum  is  a  dense  mass  of  fibrous  tissue 
containing  a  few  elastic  fibers,  which,  beginning  at  the  lateral  surface  of 
the  pia  as  a  complete  septum,  passes,  by  about  twenty-eight  serrations, 
across  the  subarachnoid  space,  and  pushing  the  arachnoid  before  it,  is 
attached  to  the  inner  surface  of  the  dura  mater.  The  serrations  of  the 
dentate  ligament  do  not  penetrate  the  subdural  space,  for  around  the 
point  of  their  attachment  the  surface  of  the  arachnoid  is  firmly  adherent 
to  the  dura  mater.  Each  serration  is  invested  by  an  endothelial  coat 
continuous  with  the  lining  of  the  subarachnoid  space. 

Blood  Supply. — The  blood  supply  of  the  central  nervous  system  is 
derived  from  vessels  which  lie  within  the  folds  of  the  pia  mater,  branches 
of  the  internal  carotid  and  the  vertebral  arteries.  The  larger  arteries 
form  an  anterior  longitudinal  group  represented  in  the  spinal  cord  by 
the  anterior  spinal  artery  and  its  branches,  and  in  the  brain  by  the  ves- 
sels of  the  circle  of  Willis  and  their  immediate  branches. 

Two  sets  of  vessels  may  be  said  to  be  distributed  from  these  sources 


THE  MENINGES  AND  BLOOD  SUPPLY  625 

— one  of  which  is  distributed  through  the  pia  mater  to  the  adjacent  white 
matter  of  the  spinal  cord  and  to  the  gray  pallium  of  the  brain;  the  other 
penetrates  the  spinal  cord  through  the  anterior  median  fissure  by  a 
series  of  small  fissural  arteries  to  be  distributed  to  the  central  gray  mat- 
ter, and  in  the  brain  is  represented  by  the  branches  of  the  middle  cere- 
bral arteries  which  penetrate  directly  to  the  ganglionic  gray  matter  in 
the  interior  of  the  cerebrum. 

In  the  spinal  cord  the  vessels  of  the  former  set  are  mostly  distributed 
to  the  white  cortex,  the  larger  branches,  however,  penetrate  the  white 
matter  and  aid  in  the  formation  of  the  capillary  network  of  the  gray 
medulla.  In  the  brain  their  distribution  is  similar,  the  smaller  pial 
vessels,  the  cortical  arteries,  being  distributed  to  the  cortex,  which  in  this 
case  is  formed  by  the  gray  matter;  the  larger,  the  medullary  arteries, 
penetrating  to  the  white  medulla  in  which  they  break  up  into  capillary 
vessels. 

The  veins  trend  in  the  opposite  direction  and  in  the  pia  mater  col- 
lect into  large  vessels,  which  in  the  brain  open  into  the  sinuses  of  the 
dura  mater,  and  which  in  the  spinal  cord  form  the  ventral  and  dorsal 
median  veins. 

All  the  larger  vessels  receive  thin  fibrous  investments  from  the  pia 
mater ;  the  smaller  vessels  and  capillaries  are  surrounded  by  neuroglia. 

There  are  frequent  anastomoses  between  the  larger  veins ;  the  arteries, 
however,  are  all  terminal  arteries  according  to  Cohnheim's  classification, 
possessing  no  anastomoses  with  the  capillary  areas  of  other  vessels. 

Neither  brain  nor  cord  possess  true  lymphatics.  The  sole  lymphatic 
representatives  within  the  central  nervous  system  are  pericellular  and 
perivascular  spaces  communicating  with  subpial  spaces  and  ultimately 
through  uncertain  clefts  and  channels  with  the  subarachnoid  spaces. 

The  bulk  of  the  cerebro-spinal  fluid  is  secreted  by  the  cells  of  the 
choroid  plexuses  directly  into  the  cerebral  ventricles.  It  escapes  into  the 
subarachnoid  spaces  through  the  roof  of  the  fourth  ventricle.  From  here 
it  is  absorbed  into  the  venous  sinuses  by  way  of  the  arachnoid  villi.  A 
small  quantity  of  cerebro-spinal  fluid  is  contributed  also  by  the  blood 
capillaries  of  the  central  nervous  system.  The  lymphlike  fluid  passes 
from  these  capillaries  directly  into  the  pericapillary  spaces  and  thence 
to  each  nerve  cell  or  outward  through  the  perivascular  channels  to  the 
subarachnoid  spaces.  Besides  the  fluid  which  escapes  through  the  venous 
sinuses  of  the  dura  a  small  amount  drains  also  by  way  of  the  perineural 
spaces  indirectly  into  the  lymphatic  system.  (See  L.  H.  Weed;  Anat. 
Rec.,  Vol.  12,  1917.) 


CHAPTER    XVIII 
THE   EYE 


GENERAL  CONSIDERATIONS 

The  eye  may  be  said  to  consist  of  the  visual  organ,  or  globe,  and  its 
appendages — the  eyelids,  conjunctiva,  and  lacrimal  apparatus — whose 
function  is  chiefly  protective. 

The  globe  of  the  eye,  or  eye  proper,  is  contained  within  the  cavity 


FIG.  536.— DISSECTION  OF  EYELIDS  AND  LACRIMAL  APPARATUS. 

1,  upper  lacrimal  gland;  2,  lower  lacrimal  gland  and  excretory  ducts;  3,  mouths 
of  excretory  ducts:  4,  tarsal  (Meibomian)  glands;  5,  puncta  lacrimalia;  6,  lacri- 
mal canaliculi;  7,  lacrimal  sac  and  nasal  duct;  8,  caruncula.  (After  Fox.) 

of  the  orbit,  its  posterior  two-thirds  being  embedded  in  a  mass  of  intra- 
orbital  fat  whose  inner  surface  is  covered  by  a  thin  fibrous  membrane  or 
fascia  which  is  clothed  with  mesenchymal  epithelium.  The  epithelium 
is  reflected  from  this  fascia  to  the  surface  of  the  ocular  globe,  along  a 
line  just  posterior  to  the  border  of  the  conjunctiva,  whence  it  passes 
over  the  surface  of  the  globe  as  far  posteriorly  as  the  optic  nerve,  on 


GENERAL  CONSIDERATIONS 


627 


the  surface  of  which  it  again  becomes  continuous  with  the  mesenchymal 
epithelium  of  the  fascia.  Thus  a  serous  sac  or  lymphatic  space  is  formed 
by  the  parietal  layer  of  this  sac,  which  lines  the  orbital  cavity,  in  conjunc- 
tion with  the  visceral  layer  which  covers  the  posterior  two-thirds  of  the 
globe  of  the  eye;  this  sac  is  the  capsule  of  Tenon. 


Iflembrana  (erminaltj 


\  centrolit 
Menus  opficm 

FIG.  537. — HORIZONTAL  SECTION  OF  THE  RIGHT  EYEBALL. 
(From  Fox,  after  Magnus.) 

The  anterior  third  of  the  globe  is  covered  by  a  reflection,  at  the 
fornix  conjunctivas,  of  the  conjunctival  layer  which  clothes  the  inner 
surface  of  the  palpebrae  or  eyelids.  The  conjunctiva  is  a  continuation  of 
the  integument  of  the  lid,  modified  so  as  to  simulate  a  mucous  membrane. 
The  portion  associated  with  the  eyelid  is  known  as  the  palpebral  con- 
junctiva, that  covering  the  eye  as  the  ocular,  bulbar  or  scleral  con  June- 


628  THE  EYE 

tiva.  Where  the  sclera  passes  into  the  cornea,  the  conjunctival  epithe- 
lium becomes  continuous  with  the  anterior  corneal  epithelium,  the  tunica 
propria  blending  with  the  corneal  stroma. 

The  globe  of  the  eye  or  eyeball  is  a  spheroidal  body  whose  surface 
consists  of  three  coats,  an  outer,  middle,  and  inner,  and  whose  contents 
are  the  vitreous  and  aqueous  humors  and  the  crystalline  lens. 

The  eyeball  is  not  a  true  sphere,  but  may  be  said  to  comprise  segments 
of  two  spheres,  the  smaller  of  which  is  inserted  into  the  anterior  surface 
of  the  larger.  The  anterior  or  smaller  segment  consists  chiefly  of  trans- 
parent tissues  which  permit  the  entrance  of  light.  Its  border  nearly 
corresponds  to  the  posterior  margin  of  the  ciliary  body,  and  it  may  be 
approximately  indicated  by  a  parallel  circle  midway  between  the  margin 
of  the  cornea  and  the  equator  of  the  eyeball.  The  anterior  segment  con- 
tains the  cornea,  the  sclerocorneal  junction,  the  anterior  and  posterior 
chambers,  the  aqueous  humor,  the  iris,  and  the  ciliary  body.  The  pos- 
terior segment  comprises  the  posterior  two-thirds  of  the  eyeball  and  in- 
cludes the  sclera,  choroid,  retina,  and,  within  these  coats,  the  vitreous 
humor.  The  crystalline  lens  with  its  suspensory  ligament  forms,  as  it 
were,  a  partition  separating  the  two  segments. 

The  optical  or  visual  axis  of  the  eye  is  a  horizontal,  anteroposterior, 
imaginary  line,  about  an  inch  in  length,  which  extends  from  the  center 
of  the  cornea  through  the  anterior  chamber,  the  center  of  the  pupillary 
opening  of  the  iris,  the  center  of  the  crystalline  lens,  and  the  center  of 
the  vitreous  humor,  and  reaches  the  fovea  centtalis  which  lies  in  the 
middle  of  a  thickened  portion  of  the  retina,  the  macula  lutea.  The  ver- 
tical and  transverse  axes  measure  about  1  mm.  less  than  the  anteropos- 
terior axis.  Toward  the  inner  side,  at  a  distance  of  3.5  mm.,  and  about 
1  mm.  below  the  center  of  the  fovea  centralis,  is  the  entrance  of  the  optic 
nerve.  This  nerve  pierces  the  coats  of  the  eye,  its  fibers  spreading  out 
in  a  radial  manner,  upon  the  inner  surface  of  the  retina. 

The  extremities  of  the  visual  axis  mark  the  two  poles  of  the  ocular 
globe;  the  anterior  extremity,  lying  in  the  center  of  the  cornea,  is  in 
the  anterior  or  smaller  spheroidal  segment,  the  posterior  extremity,  in 
the  fovea  centralis,  lies  in  the  posterior  segment  of  the  eye. 


THE  EXTERNAL  COAT— THE  FIBROUS  TUNIC 

The  outer  tunic  of  the  eyeball  includes  the  cornea,  the  sclera,  and  the 
sclerocorneal  junction. 


FIG.  538.— THE  ANTEUIOR  SEGMENT  OF  A  CHILD'S  EYE;  MERIDIONAL  SECTION. 
a,  ora  serrata;  b,  ciliary  processes;  c,  iris;  d,  crystalline  lens;  e,  ciliary  muscle;  /, 
ocular  conjunctiva;  g,  cornea;  h,  the  capsule  of  the  lens,  partially  detached.    Hema- 
tein  and  eosin.     Photo.     X  10. 

629 


630 


THE  EYE 


THE  CORNEA 

The  cornea  is  a  concavoconvex.  transparent,  colorless  disk  of  approxi- 
mately equal  thickness  (1  mm.)  throughout  all  its  portions.  It  is  nearly 
circular  in  outline,  its  horizontal  exceeding  its  vertical  diameter  by  only 


FIG.  539. — FROM  A  MERIDIONAL  SECTION  OF  THE  HUMAN  CORNEA. 

a,  anterior  corneal  epithelium;  b,  anterior  homogeneous  membrane;  c,  substantia 
propria;  d,  posterior  homogeneous  membrane;  e,  posterior  corneal  epithelium. 
Hematein  and  eosin.  Photo.  X  180. 

0.5  mm. ;  its  external  surface  is  convex,  its  internal  surface  concave.  The 
cornea  forms  the  anterior  one-fourth  of  the  tunica  externa,  and  repre- 
sents a  spheroidal  segment  whose  radius  is  somewhat  shorter  than  that 
of  the  posterior  segment  of  the  eyeball.  It  is  inserted  into  the  anterior 
margin  of  the  sclera  much  after  the  manner  in  which  a  watch-glass  is 


THE  EXTERNAL  COAT— THE  FIBROUS  TUNIC  631 

set  in  its  rim;  hence  the  inner  surface  of  the  cornea  possesses  a  slightly 
greater  diameter  than  the  outer. 

The  cornea  may  be  said  to  consist  of  five  layers:  \,  the  anterior 
epithelium;  2,  the  anterior  homogeneous  membrane;  3,  the  corneal  sub- 
stance; 4,  the  posterior  homogeneous  membrane;  5,  the  posterior  epithe- 
lium. 

The  anterior  epithelium  (corneal  epithelium,  corneal  conjunctiva) 
at  the  margin  of  the  cornea  is  continuous  with  the  scleral  portion  of  the 
conjunctiva.  It  consists  of  a  relatively  thin  layer — six  to  eight  cells 
deep — of  stratified  squamous  epithelium,  the  deepest  cells  of  which  are 
elongated  or  columnar,  the  middle  cells  polyhedral,  and  the  superficial 
cells  somewhat  flattened.  The  cells  at  all  levels  are  nucleated  and,  like 
the  other  corneal  tissues,  perfectly  transparent.  The  columnar  cells 
are  ofte'n  slender  and  much  elongated,  their  pointed  apices  extending 
well  toward  the  surface  of  the  epithelial  layer. 

The  epithelium  rests  directly  upon  the  anterior  homogeneous  lamella. 

The  deeper  cells  of  the  epithelium  present  distinct  intercellular  lym- 
phatic spaces  and  intercellular  bridges.  Between  the  cells  are  the  termi- 
nal ramifications  of  nerve  fibrils  from  the  plexus  in  the  corneal  substance. 

The  anterior  homogeneous  membrane  (anterior  basal  lamella,  elas- 
tic membrane  of  Bowman)  was  formerly  thought  to  consist  of  elastic  tis- 
sue, but  this  supposition  is  disproved  by  its  ready  solubility  on  boiling 
(His),  as  well  as  by  the  fact  that  it  does  not  react  typically  to  the  spe- 
cific stains  for  this  tissue.  Bowman's  membrane  is  apparently  a  homo- 
geneous or  structureless  coat  except  that  it  is  slightly  fibrillar  at  its 
extreme  margin  where  it  becomes  continuous  with  the  fibrous  tissue  of 
the  sclera.  It  resembles  elastic  tissue  in  that  it  is  highly  refractive  and 
possesses  a  shining  glassy  appearance.  It  does  not  stain  readily  with  the 
ordinary  dyes. 

The  corneal  substance  (substantia  propria)  forms  the  greater  por- 
tion of  the  cornea.  It  consists  of  a  lamellated  connective  tissue,  which 
forms  about  sixty  fibrous  layers,  parallel  to  the  corneal  surface.  The 
fibrous  bundles  of  these  lamellae,  being  arranged  in  meridional  curves 
parallel  to  the  surface,  appear  to  cross  one  another  at  right  angles 
in  the  central  portion  of  the  circular  cornea.  Other  fibers,  arcuate  fibers, 
pass  from  one  layer  to  another;  so' firmly  uniting  them  that  it  is  im- 
possible to  tease  the  cornea  into  its  component  lamellae. 

The  intervals  between  the  fibrous  layers  are  occupied  by  interlamel- 
lar  cement,  or  ground  substance,  in  which  lymphatic  channels  and  large 
flattened  cells,  the  corneal  corpuscles,  can  be  demonstrated.  The  cor- 


632 


THE  EYE 


neal  'corpuscles'  are  branched  lamellar  connective  tissue  cells,  which 
occupy  the  large  lymphatic  spaces  or  lacunae  of  the  interlamellar  ground 


FIG.  540. — CORNEAL  CORPUSCLES  OF  THE  FROG. 

a,  as  seen  in  tangential  section;  b,  as  seen  in  transection  of  the  cornea.    Chlorid 
of  gold.    Highly  magnified.    (After  Rollett.) 

substance,  and  which  send  fiber-like  processes  into  the  interlacing  lym- 
phatic channels. 

The  posterior  homogeneous  membrane,  or  membrane  of  Descemet 
(posterior  basal  lamella),  is  similar  in  structure  to  the  anterior.     Like 


THE  EXTERNAL  COAT— THE  FIBROUS  TUNIC 


633 


the  latter,  though  formerly  considered  an  elastic  membrane  it  does  not 
give  the  specific  reactions  of  elastic  tissue.  It  is  somewhat  thicker  than 
Bowman's  membrane.  At  its  margin  the  membrane  is  continuous  with 
fibrous  bundles  which  are  directed  outward  into  the  ligamentum  pectina- 
tum,  and,  at  least  in  some  animals,  through  this  ligament  into  the  ciliary 
margin  of  the  iris.  The  membrane  of  Descemet  can  be  readily  detached 
from  the  corneal  substance  by  teasing.  It  prevents  filtration  of  fluid 
from  the  anterior  chamber  into 
the  corneal  stroma. 

The  posterior  epithelial  layer 
(corneal  cndothelium)  is  a  mes- 
enchymal  epithelium  consisting 
of  clear,  cuboidal  or  flattened 
cells,  placed  edge  to  edge,  and 
bound  together  by  intercellular 
bridges.  At  the  margin  of  the 
cornea  it  is  reflected  over  the 
lateral  wall  of  the  anterior 
chamber  to  the  anterior  surface 
of  the  iris.  Its  cells  rest  upon 
the  posterior  homogeneous  mem- 
brane. 

All  the  tissues  of  the  cornea, 
during  life,  are  absolutely  trans- 
parent. The  elements  of  which  they  consist  are  of  almost  identical 
refractive  indices,  and  about  that  of  water,  so  that  in  fresh,  or  in 
living  tissue,  it  is  almost  impossible  for  the  microscope  to  discover  any 
of  the  structure  of  the  cornea.  After  death  the  cornea  becomes  opaque 
and  its  elements  are  then  easily  distinguished. 

Vascular  and  Nerve  Supply. — The  cornea  itself  is  an  absolutely 
non-vascular  tissue,  having  neither  blood  nor  true  lymphatic  vessels. 
It  is,  however,  well  supplied  with  nerve  fibers,  derived  from  the  ciliary 
nerves,  which  form  an  annular  plexus  in  the  sclera  about  the  margin 
of  the  cornea,  from  which  point  bundles  of  naked  axis-cylinders  pass 
into  the  corneal  substance  to  form  a  basal  plexus,  near  the  anterior  homo- 
geneous membrane.  From  this  latter  plexus,  fibers  are  distributed  to 
the  corneal  substance  and  to  a  subepithelial  plexus,  anterior  to  Bowman's 
membrane,  whence  the  terminal  sensory  fibrils  penetrate  the  anterior 
epithelium.  For  a  distance  of  several  millimeters  within  the  margin  of 
the  cornea  special  nerve  endings  (bulbous  corpuscles)  may  also  occur. 
40 


FIG.  541. — CORNEAL  CELLS,  ISOLATED. 
Highly  magnified.     (After  Waldeyer.) 


634  THE  EYE 

THE  SCLERA 

The  sclera  (sclerotic  coat)  is  a  firm  opaque  connective  tissue  mem- 
brane which  forms  the  outermost  layer  of  the  posterior  segment  of  the 
eyeball.  It  consists  of  two  layers,  the  thick,  firm,  substantia  propria, 
and  the  very  thin,  innermost,  delicate,  lamina  fusca. 

By  reflected  light  the  sclera  of  the  adult  is  of  a  lustrous  white  color. 
In  the  child  it  has  a  faint  bluish  tint,  due  to  the  presence  of  pigment  in 
the  deeper  layers  of  the  child's  eye  which  shows  indistinctly  through 
the  relatively  clear  superficial  tissues.  The  anterior  portion  of  the 
sclera  is  covered  by  the  bulbar  conjunctiva  and  is  familiarly  known  as 
the  'white  of  the  eye.'  A  yellowish  patch  in  the  vicinity  of  the  corneal 
margin,  known  as  the  pinguecula,  may  be  present,  especially  in  old 
age.  It  is  believed  to  be  due  to  irritation  from  dust,  leading  to  colloid 
infiltration  of  the  conjunctival  stroma. 

That  portion  of  the  sclera  which  is  posterior  to  the  ocular  equator 
is  covered  by  the  visceral  layer  of  the  capsule  of  Tenon  except  at  the 
insertions  of  the  straight  and  oblique  muscles.  The  tendons  of  these 
muscles  pierce  the  capsule  and  are  obliquely  inserted  into  the  surface  of 
the  sclera  in  a  line  nearly  corresponding  to  the  equator  of  the  eye.  The 
tendon  bundles  of  the  muscles  are  directly  continuous  with  the  fibrous 
bundles  which  compose  the  sclera. 

The  Substantia  Propria.— The  collagenous  fibrous  tissue  of  the 
sclera  is  disposed  in  bundles  which  are  arranged  along  meridional  and 
equatorial  lines;  they  interlace  with  one  another  to  form  a  dense  net- 
work. A  few  elastic  fibers  are  interspersed  among  the  bundles  of  this 
network.  Stellate  connective  tissue  cells,  the  scleral  corpuscles,  lie  in  the 
interfascicular  clefts.  Occasional  pigmented  cells  are  also  sometimes 
present. 

The  Lamina  Fusca. — The  inner  surface  of  the  sclera  presents  a  fine 
gauzy  membrane  which  can  be  readily  detached  by  teasing.  This  is  the 
lamina  fusca  sclerae.  It  consists  of  delicate  interlacing  fibrous  bundles 
and  numerous  pigmented  connective  tissue  cells.  The  lamina  fusca  near 
the  posterior  pole  is  firmly  adherent  to  the  scleral  substance. 

At  the  posterior  pole  of  the  eye  the  sclera  is  pierced  by  the  optic 
nerve,  whose  numerous  bundles  penetrate  the  coats  of  the  eyeball  and 
give  to  this  portion  of  the  sclera  a  cribrose  appearance.  This  area  of  the 
sclerotic  coat  is  known  as  the  lamina  cribrosa  sclerce.  It  is  a  circular 
zone  whose  border  is  outlined  by  the  entrance  of  the  posterior  ciliary 
arteries  and  the  ciliary  nerves.  This  is  the  thickest  portion  of  the  sclera, 


THE  EXTERNAL  COAT— THE  FIBROUS  TUNIC  635 

the  coat  becoming  progressively  thinner  toward  the  equator  of  the  eye; 
near  its  anterior  margin  it  is  again  thickened  by  the  tendinous  insertions 
of  the  extrinsic  muscles. 

The  sclera  is  chiefly  supplied  by  branches  from  the  posterior  ciliary 
arteries,  which  form  a  wide-meshed  plexus  in  its  substance,  its  vessels 
anastomosing  freely  with  those  of  the  choroid  coat. 

THE   SCLEROCORNEAL   JUNCTION 

The  sclerocorneal  junction  (Fig.  543)  is  a  narrow  circular  zone  at 
the  margin  of  the  cornea,  where  it  is  inserted  into  the  sclera.  Across 
this  narrow  zone  the  fibrous  bundles  of  the  opaque  sclera  are  continued 
directly  into  the  similar,  though  perfectly  transparent,  bundles  of  the 
cornea!  substance. 

The  anterior  or  outer  surface  of  this  zone  is  covered  by  the  ocu- 
lar portion  of  the  conjunctiva.  Its  epithelium  is  of  the  stratified  squam- 
ous  variety  and  is  continuous  with  the  anterior  epithelium  of  the  cor- 
nea. 

From  the  inner  surface  of  this  junctional  zone  the  anterior  extremi- 
ties of  the  muscle  fibers  composing  the  ciliary  muscle  take  their  origin. 
The  fibers  of  this  muscle  intermingle  with  the  marginal  fibers  of  the 
posterior  homogeneous  layer  of  the  cornea  to  form  the  Ugamentum 
pectinatum,  which  connects  the  sclerocorneal  junction  with  the  base  of 
the  iris.  This  pectinate  ligament  is  very  much  more  highly  developed  in 
certain  animals,  e.g.,  cow  and  horse,  than  in  man. 

Toward  the  inner  side  of  the  scleral  margin  and  near  the  border 
of  the  cornea  is  the  canal  of  Schlemm  (sinus  venosus  sclerce}.  This 
is  an  annular  venous  channel  (or  network  of  channels),  draining  into 
the  anterior  ciliary  veins.  Though  venous  in  character  it  serves  also 
as  a  drainage  channel  for  the  lymphatic  spaces  of  Fontana,  which  lie  in 
the  lateral  wall  of  the  anterior  chamber  and  between  the  fiber  bundles 
of  the  ligamentum  pectinatum.  The  spaces  of  Fontana  are  true  lym- 
phatic spaces  and  are  in  communication  with  the  anterior  chamber  of 
the  eye. 

Through  the  canal  of  Schlemm,  the  aqueous  humor  of  the  anterior 
chamber  is  put  into  communication  with  the  veins  of  the  sclera,  and 
a  system  is  thus  formed  by  which  the  intra-ocular  pressure  is  maintained 
at  normal.  A  blocking  of  the  canal  of  Schlemm  interferes  with  the 
drainage  of  the  anterior  chamber,  and  is  believed  to  produce  the  serious 
pathologic  condition  of  the  eyeball,  known  as  glaucoma,  due  to  progres- 


636  THE  EYE 

sive  increase  of  infra-ocular  tension  which  causes  atrophy  of  the  optic 
nerve  and  the  retina. 

Blood  Supply.  — The  sclerocorneal  junction  is  abundantly  supplied 
\vith  blood  from  the  anterior  ciliary  vessels,  which,  with  the  posterior 
conjunctival  vessels,  form  loops  at  the  margin  of  the  cornea  and  anasto- 
mose freely  with  the  vessels  of  the  ciliary  body.  The  sclera  contains  no 
true  lymphatic  vessels. 


THE  MIDDLE  COAT— THE  VASCULAR  TUNIC 

The  middle  tunic  (uvea,  uveal  tract]  includes  the  choroid  coat, 
ciliary  body,  and  iris.  The  latter  is  perforated  centrally  by  an  approxi- 
mately circular  aperture,  the  pupil. 

The  iris  divides  the  cavity  of  the  anterior  segment  of  the  eye  into  an 
anterior  chamber,  included  between  it  and  the  posterior  or  inner  surface 
of  the  cornea,  and  a  posterior  chamber,  which  is  bounded  by  the  iris  in 
front  and  the  crystalline  lens  and  its  suspensory  ligament  behind. 
The  free  or  pupillary  margin  of  the  iris  is  in  light  contact  with  the 
anterior  surface  of  the  lens.  The  posterior  chamber  is  therefore  an  an- 
nular compartment. 

THE  CHOROID  COAT 

The  choroid  coat  (tunica  clioroidea)  consists  of  three  layers:  1,  the 
lamina  suprachoroidea ;  2,  the  lamina  vascularis ;  3,  the  lamina  capillaris. 
The  function  of  the  very  vascular  choroid  is  to  supply  nutrition  to  the 
outer  portions  of  the  retina. 

The  lamina  suprachoroidea  (suprachoroid  layer}  is  a  very  delicate 
membrane  which  contains  many  pigmented  cells  and  is  similar  in  struc- 
ture to  the  lamina  fusca  of  the  sclera. 

The  flattened  pigmented  cells  are  brownish-black  in  color  from  the 
many  coarse  granules  which  they  contain,  and  are  irregularly  disposed, 
either  separately  or  in  groups.  Lymphatic  spaces  occur  between  this 
layer  and  the  sclera  and  communicate  through  the  interfascicular  lym- 
phatic clefts  of  the  sclera  with  the  capsule  of  Tenon. 

The  fibers  of  this  layer  are  not  only  distributed  in  its  own  plane  but 
pass  obliquely  to  the  lamina  fusca,  thus  loosely  attaching  the  supracho- 
roid layer  to  the  sclera.  Similar,  obliquely  disposed  fibers  pass  to  the 
deeper  portions  of  the  choroid,  with  the  fibers  of  which  they  blend. 

The  lamina  vasculosa    (vascular  layer,  clioroid  proper),  so  called 


THE  MIDDLE  COAT— THE  VASCULAE  TUNIC 


637 


because  it  contains  the  ramifications  of  the  ciliary  arteries  and  veins, 
is  by  far  the  thickest  of  the  three  layers  of  the  choroid.  It  may  be  ar- 
bitrarily separated  into  an  outer  stratum,  consisting  chiefly  of  dense 
interlacing  bundles  of  connective  tissue  fibers  which  inclose  only  the 
larger  blood-vessels,  and  an  inner  stratum  of  similar  structure,  but  every- 
where permeated  by  a  close  network  of  small  vascular  twigs.  So  dense 
is  this  network  near  the  posterior  pole  of  the  eye,  as  to  give  the  layer 
the  appearance  of  an  almost  continuous  sheath  of  small  blood-vessels. 

The  Lamina  Capillaris. — Within  the  vascular  layer  is  the  capillary 
membrane   (lamina  capillaris,  lamina  choriocapillaris,  tunica  Euyschi- 


FIG.  542. — FROM  A  MERIDIONAL  SECTION  OF  THE  CHOROID  COAT. 

a,  membrane  of  Bruch;  b,  the  inner  margin  of  the  vascular  layer.  Between  a 
and  b  is  the  capillary  layer  or  choriocapillaris;  c,  venule  containing  blood  cor- 
puscles; d,  fibrous  layer  of  the  choroid  or  lamina  suprachoroidea.  Highly  magni- 
fied. (After  Cadiat.) 

ana),  which  contains  an  exceedingly  close-meshed  capillary  network. 
This  network  is  specially  dense  near  the  macula  lutea  at  the  posterior  pole 
of  the  eyeball.  Its  inner  surface  forms  a  very  thin  homogeneous  mem- 
brane, the  lamina  basalis,  lamina  vitrea  or  membrane  of  Bruch,  which 
increases  somewhat  in  thickness  as  age  advances.  The  inner  surface 
of  the  lamina  basalis  is  indented  by  the  bases  of  the  adjacent  pigment 
cells  of  the  retina.  Anteriorly  the  vessels  of  the  choriocapillaris,  like 
those  of  the  vascular  layer,  become  continuous  with  the  vessels  of  the 
ciliary  body  and  iris. 

Between  the  pars  vascularis  and  the  choriocapillaris  may  be  distin- 
guished a  narrow  dense  fibre-elastic  boundary  zone,  free  of  pigment. 
In  ruminants  this  layer  becomes  pronounced,  due  to  the  presence  of  ro- 
bust connective  tissue  fibers,  and  is  known  as  the  tapetum  fibrosum. 
This  layer  gives  to  the  eyes  of  ruminants  their  characteristic  metallic 
luster.  In  the  eyes  of  carnivora  and  certain  fishes  the  tapetum  is  com- 
posed of  rectangular  epithelioid  cells,  filled  with  peculiar  glistening 


638  THE  EYE 

crystals  giving  to  these  eyes  an  iridescent  sheen,  and  is  known  as  the 
tapetum  cellulosum. 

THE  CILIARY  BODY 

The  ciliary  body  (corpus  ciliare}  represents  the  thickened  anterior 
border  of  the  choroid  coat.  It  is,  therefore,  of  annular  shape  and  occu- 
pies a  zone  whose  posterior  border  blends  with  the  choroid  at  a 
point  opposite  the  ora  serrata  of  the  retina,  and  whose  anterior 
margin  is  continued  into  the  iris  opposite  the  sclerocorneal  junction. 
It  may  be  said  to  consist  of  three  structures  arranged  in  layers  of  vary- 
ing thickness:  1,  the  ciliary  muscle;  2,  the  fibrous  layer  with  its  ciliary 
processes;  and  3,  that  portion  of  the  pigmented  epithelium  of  the  retina 
which  constitutes  the  pars  ciliaris  reiince  or  ciliary  epithelium,  and 
covers  the  inner  surface  of  the  ciliary  body.  The  suspensory  ligament  of 
the  crystalline  lens  is  attached  to  the  inner  surface  of  the  retinal  epithe- 
'lium  of  the  ciliary  processes  and  grooves. 

The  ciliary  muscle  consists  of  an  annular  mass  of  non-striated  fibers 
which  arise  from  the  inner  surface  of  the  sclera  near  the  sclerocorneal 
junction,  and  are  inserted  into  the  entire  breadth  of  the  fibrous  mass 
of  the  ciliary  body  as  far  back  as  the  anterior  margin  of  the  choroid. 
The  muscle  fibers  are  divisible  into  three  sets,  according  to  the  direction 
of  their  long  axis;  these  are  the  meridional,  the  radial,  and  the 
circular. 

The  meridional  fibers  form  the  outer  and  greater  portion  of  the  mus- 
cle. They  begin,  just  posterior  to  the  corneal  margin,  taking  their 
origin  from  the  inner  surface  of  the  sclera,  and  radiate  backward  in  a 
meridional  direction  for  a  variable  distance,  to  be  finally  inserted  into 
the  fibrous  bundles  of  the  posterior  half  of  the  ciliary  body  (ciliary  ring), 
the  longest  fiber  bands  passing  as  far  back  as  the  choriociliary  junction, 
where  they  are  attached  to  the  anterior  margin  of  the  choroid. 

The  radial  fibers  simulate  the  meridional  fibers  in  that  they  radiate 
from  the  corneal  margin.  They  pursue,  however,  a  shorter  course. 
From  their  origin  they  pass  backward  with  a  sharp  inward  curve  to 
assume  a  direction  which  approaches  that  of  the  radii  of  the  ocular  globe 
(hence  their  name) ;  they  are  inserted  into  the  anterior  half  of  the  fibrous 
layer  of  the  ciliary  body.  Their  radial  disposition  becomes  progressively 
more  apparent  toward  the  axial  margin  of  the  ciliary  body.  These 
fibers  are  far  less  numerous  than  the  meridional. 

The  circular  fibers  comprise  numerous  small  non-striated  muscle 
bundles  which  are  interspersed  among  the  bundles  of  radial  fibers. 


640  THE  EYE 

They  are  disposed  in  a  circular  direction  about  the  axial  margin  of  the 
ciliary  body  on  its  outer  surface,  and  hence  are  in  relation  with  the  inner 
surface  of  the  sclerocorneal  junction  and  the  outer  margin  of  the 
base  of  the  iris.  The  circular  muscle  fibers  are  also  interspersed  among 
the  fibers  of  the  ligamentum  pectinatum,  which  pass  in  a  radial  manner 
from  the  margin  of  the  posterior  homogeneous  membrane  of  the  cornea 
to  the  base  of  the  iris  and  anterior  margin  of  the  ciliary  body.  The 
circular  fibers  are  said  to  be  deficient  or  even  absent  in  myopic  eyes,  but 
are  exaggerated  in  hypermetropic  eyes. 

The  disposition  of  the  ciliary  muscle  fibers  is  such  that  during  con- 
traction the  fibrous  ciliary  body  and  the  base  of  the  iris  are  drawn 
forward,  the  choroid  is  made  tense,  and  the  suspensory  ligament  of  the 
lens  is  relaxed.  The  lens  then  becomes  more  nearly  spherical  because 
of  its  own  elasticity. 

The  fibrous  layer  of  the  ciliary  body  consists  of  connective  tissue, 
and  connects  the  fibrous  portion  of  the  choroid  to  the  similar  tissue  of  the 
iris.  It  is  formed  by  a  reticulum  of  the  fine  fibers  in  the  meshes  of 
which  are  numerous  lamellar  and  a  few  pigmented  cells.  Buried  within 
the  outer  portion  of  this  fibrous  mass  and  intermingling  with  its  fibers 
are  the  fiber  bundles  of  the  ciliary  muscle.  Into  the  inner  portion  of  the 
fibrous  layer  a  vascular  plexus  is  continued  from  the  vascular  and  capil- 
lary layers  of  the  choroid;  branches  of  the  ciliary  arteries  communicate 
with  this  plexus. 

Appended  to  the  inner  surface  of  the  fibrous  layer  are  numerous 
meridionally  disposed  folds  of  connective  tissue  which  radiate  from,  the 
base  or  outer  margin  of  the  iris  to  the  margin  of  the  choroid  opposite  the 
ora  serrata.  These  are  the  ciliary  processes.  Their  inner  or  free  surface 
is  covered  by  the  pigmented  retinal  epithelium,  and  within  these  proc- 
esses are  contained  the  greater  portion  of  the  pigmented  connective  tissue 
cells  of  the  ciliary  body.  Each  fold  is  much  deeper  (about  1  mm.) 
toward  its  axial  margin  and  becomes  progressively  diminished  in  height 
toward  the  choroid. 

The  pigmented  epithelial  layer  is  here  and  there  invaginated  into 
the  fibrous  tissue  of  the  ciliary  processes  to  form  ampullate  recesses 
(the  ciliary  glands),  which  somewhat  resemble  true  secreting  glands. 
These  so-called  glands  have  been  supposed  to  be  concerned  in  the  secre- 
tion of  the  aqueous  humor.  They  are  probably  not  true  secreting  glands, 
but  represent  mere  invaginations  of  the  epithelium. 

The  ciliary  epithelium  (pars  ciliaris  retinae)  consists  of  a  double 
layer  of  epithelial  cells,  continuous  posteriorly  with  the  retina,  and  in 


THE  MIDDLE  COAT— THE  VASCULAE  TUNIC  641 

front  with  the  pars  iridica  retinae.  The  superficial  (innermost)  cells 
present  a  clear  or  slightly  granular  cytoplasm  with  a  centrally  situated 
nucleus.  Their  cytoplasm  is  but  slightly  pigmented,  and  ofttimes  is 
indistinctly  rodded  or  fibrillated.  In  shape,  these  cells  are  of  the  low 
columnar  type,  but  they  become  progressively  flattened  toward  the  iris, 
where  they  are  continuous  with  the  pars  iridica  retinae.  They  represent 
a  continuation  of  the  sustentacular  cells  of  the  retina. 

The  cells  of  the  deeper  (outer  or  anterior)  layer  vary  in  height  from 
a  low  columnar  at  the  ora  serrata  to  a  somewhat  flattened  cell  near  the 
iridal  margin,  and  are  continuous  with  the  pigmented  cell  layer  of  the 
retina.  This  cell  layer  is  deeply  pigmented,  the  entire  cytoplasm  being 
filled  with  the  dark  brown  pigment  granules.  The  nucleus,  however, 
as  in  the  pigmented  cells  of  the  choroid,  contains  no  pigment,  and 
therefore,  in  unstained  preparations,  appears  under  the  microscope  as 
a  clear  opening  in  the  dark  background  of  pigmented  cytoplasm. 

THE  IRIS 

The  iris  (Figs.  538  and  543)  forms  an  annular  curtain  which  pro- 
jects from  the  anterior  margin  of  the  ciliary  body  toward  the  axis 
of  the  eye.  It  presents  a  central  circular  opening,  the  pupil,  which  lies 
in  the  visual  axis. 

The  iris  is  suspended  in  the  aqueous  humor,  its  pupillary  margin 
resting  gently  upon  the  anterior  surface  of  the  lens,  its  base  or  ciliary 
margin  being  separated  from  the  lens  by  an  interval,  the  posterior 
chamber,  which  is  also  filled  by  the  aqueous  humor. 

The  iris  may  be  said  to  consist  of  three  layers:  1,  the  external 
epithelium;  2,  the  fibrous  stroma;  3,  the  internal  epithelium. 

The  external  epithelium  (endothelium  of  the  iris)  is  a  mesen- 
chymal  epithelium  continuous  at  the  margin  of  the  anterior  chamber 
with  the  posterior  epithelial  layer  of  the  cornea,  which  appears  to  be 
reflected  upon  the  anterior  surface  of  the  iris.  At  the  pupillary  border 
it  is  also  continuous  with  the  internal  epithelium  of  .the  iris  (pars  iridica 
retinas).  The  cells  of  the  anterior  or  external  epithelium  are  very  much 
flattened  and  almost  endothelioid  in  appearance;  at  occasional  intervals 
the  epithelium  is  incomplete.  These  intervals  occur  either  near  the 
pupillary  or  the  ciliary  margin,  and  correspond  to  recesses  which  open 
directly  into  the  fibrous  stroma  of  the  iris  and  become  continuous  with 
its  lymphatic  interstices. 

To  the  naked  eye  the  anterior  surface  of  the  iris  presents  an  uneven 


G42  THE  EYE 

appearance,  which  is  apparently  due  to  the  presence  of  slight  meridional 
ridges,  with  shallow  intervals,  which  extend  from  the  pupillary  margin 
of  the  iris  to  its  outer  border.  The  lighter  radial  and  circular  markings 
are  due  to  the  blood-vessels. 

The  fibrous  stroma  of  the  iris  (pars  choroidalis  iriilis,  i>arx  in-ealis 
iridis)  consists  of  a  loose  spongy  connective  tissue  of  an  almost  embry- 
onal type.  Its  fibers  are  scanty  and  are  gathered  into  small  bundles, 
which  interlace  somewhat,  but  which  are  for  the  most  part  disposed  in 
a  meridional  direction.  This  disposition  is  especially  noticeable  near 
the  ciliary  margin. 

The  fibrous  stroma  is  very  rich  in  connective  tissue  cells,  which  are 
mostly  stellate  and  branch  and  interlace  freely.  They  contain  more  or 
less  brownish  pigment,  which  is  most  abundant  near  the  posterior  (in- 
ner) surface.  The  color  of  the  iris,  when  viewed  with  the  naked  eye, 
is  dependent  upon  the  depth  of  pigmentation  in  these  connective  tissue 
cells,  as  well  as  in  the  cells  of  the  internal  epithelial  layer,  and  to  the 
relative  transparency  of  the  stroma.  In  dark  blue  and  black  eyes  tb<e 
stroma  pigment  is  scanty,  and  the  very  dark  epithelial  pigment  shows 
through  the  more  anterior  clear  layers  of  the  iris.  In  the  brown  eye 
the  stroma  pigment  is  dense  and  opaque.  A  gray  color  is  produced  by 
a  scanty  stroma  pigment  clouded  by  a  rather  dense  fibrous  stroma.  In 
the  eyes  of  albinos  the  iris  lacks  pigment  altogether;  the  pink  color 
of  the  iris  is  due  to  the  blood  in  the  numerous  vessels  of  the  stroma. 

Embedded  in  the  fibrous  stroma,  near  its  pupillary  margin,  is  a 
small  bundle  of  non-striated  muscle  fibers,  which  are  circularly  disposed, 
to  form  the  so-called  sphincter  muscle  of  the  iris.  Its  fibers  are  distrib- 
uted in  a  plane  parallel  to  the  surface  of  the  iris,  and  within  the  inner 
(posterior)  part  of  its  fibrous  stroma.  They  are  most  abundant  near 
the  pupillary  margin,  and  become  progressively  thinner  toward  the 
base  of  the  iris.  Internally  to  the  "sphincter  muscle,  and  in  contact 
with  the  basement  membrane  of  the  internal  epithelium,  is  an  incom- 
plete layer,  more  distinct  toward  the  ciliary  margin  of  the  iris,  which 
contains  radially  disposed  smooth  muscle  fibers,  the  dilator  muscle  of 
the  iris,  apparently  of  ectodermal  origin.  Mydriatics  (e.g.,  atropin)  pro- 
duce an  enlargement  of  the  pupil,  presumably  through  inhibition  of 
the  constrictor  and  stimulation  of  the  dilator  muscles ;  miotics  (e.g., 
morphin)  produce  a  contrary  effect. 

The  stroma  of  the  iris  is  exceedingly  vascular,  the  arteries  and  veins 
being  meridionally  disposed,  the  capillaries  forming  an  irregular  plexus. 
Xear  the  pupillary  margin  the  vessels  form  a  rich  capillary  anastomosis, 


THE  POSTERIOR  CHAMBER  643 

the  circulus  minor.    The  entering  arteries  likewise  form  a  circulus  major 
by  anastomoses  at  the  ciliary  margin  of  the  iris. 

The  internal  epithelium  (posterior  epithelium,  pars  iridica  retina) 
resembles  that  of  the  ciliary  body  or  pars  ciliaris  retina?,  with  whic-lr 
it  is  continuous.  The  innermost  (superficial)  layer  of  epithelial  cells, 
in  the  iridal  epithelium,  is  deeply  pigmented  and  somewhat  flatter  than 
in  the  ciliary  body.  The  pigmentation  is  so  deep  that  in  the  adult  iris 
it  is  scarcely  possible  to  distinguish  the  two  epithelial  layers.  These  can, 
however,  be  readily  seen  in  the  fetal  eye,  and  even  in  that  of  the  child. 

THE  ANTERIOR  CHAMBER 

The  anterior  chamber  is  bounded  in  front  by  the  posterior  (internal) 
surface  of  the  cornea,  and  behind  by  the  anterior  surface  of  the  crystal- 
line lens  and  the  anterior  (external)  aspect  of  the  iris;  it  contains  the 
aqueous  humor  presumably  largely  a  filtration  product  from  the  numer- 
ous blood-vessels  of  this  region,  in  part  a  secretion  product  of  the  ciliary 
epithelium.  Its  anterior  boundary  is  convex,  its  posterior  concave,  and 
its  circular  margin  is  limited  by  an  area  which  is  known  as  the  irido- 
corneal  angle. 

At  this  angle  the  mesenchymal  epithelium  is  reflected  from  the  poste- 
rior surface  of  the  cornea  upon  the  anterior  surface  of  the  iris.  The 
latter  portion  of  the  epithelial  layer  is  incomplete,  since  it  presents  nu- 
merous openings  which  communicate  with  the  lymphatic  spaces  between 
the  fibers  of  the  ligamentum  pectinatum  and  ciliary  muscle.  These  lym- 
phatic recesses  are  the  spaces  of  Fontana. 

The  ligamentum  pectinatum  consists  of  fibers  which  arise  from 
the  margin  of  Descemet's  membrane,  and  pass  backward  and  inward, 
in  a  radial  direction,  to  the  fibrous  stroma  of  the  iris  and  ciliary  body. 
Viewed  from  the  cavity  of  the  anterior  chamber  the  fibers  of  this  liga- 
ment, with  the  intervening  spaces  of  Fontana,  present  a  toothed  appear- 
ance; the  ligament  derives  its  name  from  this  peculiarity. 

THE  POSTERIOR   CHAMBER 

The  posterior  chamber  is  an  annular  cavity,  somewhat  triangular  or 
trapezoidal  in  transection,  whose  lumen,  like  that  of  the  anterior  cham- 
ber, is  occupied  by  aqueous  humor,  suspended  in  which  are  the  fibers 
of  the  suspensory  ligament  of  the  crystalline  lens. 


644  THE  EYE 

It  is  limited  anteriorly  by  the  internal  surface  of  the  iris,  and  an- 
tero-externally  by  the  ciliary  processes.  Its  postero-internal  boundary 
is  formed  by  the  marginal  portion  of  the  lens,  together  with  the  adjacent 
portion  of  the  hyaloid  membrane,  which  incloses  the  vitreous  humor. 


THE  INTERNAL  COAT— THE  NERVOUS  TUNIC 

The  internal  coat  of  the  eyeball  is  divisible  into  three  portions: 
1,  the  pars  optica  retinae  or  retina  proper;  2,  the  pars  ciliaris  retina?, 
and  3,  the  pars  iridica  retina?. 

The  last  two  portions,  though  morphologically  continuous  with  the 
pars  optica  retinae,  differ  therefrom  in  their  physiological  function ;  they 
respectively  form  the  innermost  layer  of  the  ciliary  body  and  iris.  As 
such  they  have  already  been  described. 

GENERAL  CONSIDERATION  OF  THE  EETINA 

The  retina  (pars  optica  retince)  may  be  said  to  be  formed  by  the 
radial  expansion  of  the  fibers  of  the  optic  nerve  which  enter  the  eye  at 
the  inner  side  of  its  posterior  pole,  piercing  the  sclera  and  choroid  and 
spreading  out  over  the  inner  surface  of  the  eyeball. 

These  nerve  fibers  arise  from  groups  of  nerve  cells  which  are  disposed 
in  layers  to  form  the  optic  and  retinal  ganglia  (ganglion  nervi  optici 
and  ganglion  retince).  The  association  of  nerve  cells  and  fibers  with 
their  supporting  tissues  forms  the  inner,  cerebral.,  or  neural  portion  of 
the  retina.  The  dendritic  arborizations  of  many  of  these  nerve  cells  lie 
within  the  outer  half,  or  neuro-epithelial  portion  of  the  retina. 

The  retina  may  be  said  to  extend  forward  from  the  entrance  of  the 
optic  nerve  (optic  disk)  as  far  as  the  posterior  margin  of  the  ciliary 
body,  where  it  apparently  ends  abruptly  with  an  indented  border,  the 
ora  serrata.  From  this  border  the  retina  is  continued  farther  forward, 
but  only  as  the  dark  pigmented  layers  of  the  ciliary  processes  and  iris. 
In  the  usual  preparations  these  layers  contrast  intensely  with  the  opaque 
white  color  of  the  true  retina.  Like  all  the  other  tissues  which  are 
placed  in  the  optical  axis  of  the  eye,  the  retina,  during  life,  with  the  ex- 
ception of  its  pigment  layer,  is  perfectly  transparent,  but  becomes 
opaque  immediately  after  death  or  local  injury. 

The  retina  presents  on  its  inner  surface  a  slightly  elevated  yellow 
spot,  the  macula  lutea,  which  lies  exactly  at  the  posterior  pole  of  the 


THE  INTERNAL  COAT— THE  NERVOUS  TUNIC 


645 


visual  axis.  The  forea  centralis  is  the  slight  depression  in  the  center 
of  the  macula  lutea,  and  is  the  result  of  an  apparent  thinning  of  the 
retinal  layers  at  this  point. 

The  papilla  optica,  or  entrance  of  the  optic  nerve,  also  forming  a 
slight  elevation  with  a  central  depression,  the  physiologic  excavation, 
is  placed  3.5  to  4  mm.  to  the  nasal  side  of  the  macula  lutea,  and  at  a 
slightly  lower  horizontal  plane. 


DEVELOPMENT  OF  THE  EYE 

A  word  as  to  the  development  of  the  organ  will  make  clearer  the 
description  of  the  several  layers  of  the  retina.  The  retina  is  developed 
as  an  evagination  of  the  first  cerebral  vesicle,  and  is,  therefore,  to  be  re- 
garded as  a  detached  lobe  of  the  cerebrum  itself.  The  evagination  or 
optic  vesicle  grows  forward 
in  the  embryo,  and  soon 
forms  a  flask-shaped  process 
whose  expanded  extremity 
is  early  infolded  in  a  cup- 
like  manner  forming  the 
optic  cup.  The  peripheral 
layer  of  the  cup  becomes 
the  pigmented  layer,  the 
lining  layer  differentiates 
into  the  neural  layers,  of 
the  retina.  The  inferior 
surface  of  this  optic  cup 
and  the  connecting  optic 
stalk  at  first  presents  a 
s  1  i  t  - 1  i  k  e  deficiency,  the 
choroidal  fissure,  into  which 
grows  the  mesoblastic  tis- 
sue which  ultimately  forms 
the  vitreous  humor  and 
conveys  the  central  artery 
of  the  optic  nerve.  The 

indented  extremity  of  the  optic  cup  is  soon  occupied  by  the  developing 
lens,  uliich  arises,  under  the  influence  of  the  optic  cup  itself  (Lewis, 
Amer.  Jour,  of  Anat.,  1904),  but  is  formed  from  the  overlying  area  of 
the  epidermal  ectoderm. 


DEVELOPING  EYE  IN  MERID- 
IONAL SECTION;  DIAGRAMMATIC. 

A,  early;  B,  later  stage.  E,  E,  ectoderm;  L, 
lens;  M,  M,  mesoblast;  a,  optic  vesicle,  pro- 
truding from,  6,  the  first  cerebral  vesicle;  c,  a 
thickening  of  the  ectoderm,  anlage  of  the  lens; 
o,  constricted  pedicle  of  the  optic  cup;  p,  outer 
coat  of  the  optic  vesicle,  anlage  of  the  retinal 
epithelium;  r,  inner  wall  of  the  vesicle,  anlage 
of  the  neural  portion  of  the  retina.  (After 
Fuchs.) 


646  THE  EYE 

According  to  certain  investigators  (Szily,  1908,  et  al.)  the  definitive 
vitreous  humor  is  preceded  by  a  primitive  structure  in  the  form  of  a  loose- 
meshed  reticulum  of  protoplasmic  fibers  (cytodesmata)  derived  from,  and 
in  continuity  with,  both  the  lens  and  the  retina, 
^^^^  hence  ectodermal  in  origin.     This  primitive  vi- 

,/^J*          i^L  treous  body  is  subsequently  invaded  by  vascular 

Ka  mesenchyma,  the  two  tissues  uniting  to  produce 

ot^dBb  Hi  the  definitive  vitreous.     The  hyaloid  membrane, 

surrounding  the  vitreous  body,  and  the  fibers  of 

^^^•^^B^^^  the  suspensory  ligament  of  the  lens  are  thought 

0  by   some  to   represent   the  persistent  peripheral 

FIG.  545.— SCHEMATIC  RE-      remains     of    the    original    ectodermal     stroma. 

CONSTRUCTION   OF   THE      Others,    among    them    most    recently    Baldwin 

DEVELOPING  EYE.  (Arch.  mikr.  Anat.,  vol.  80,  1912),  describe  the 

a.opticcupjs.choroidal      origin  of  the  susPensory  ligament  from  mesen- 

fissure;  «„  optic  nerve;  L,      chyme. 

developing    lens.      (After  Failure  of  closure  on  the  part  of  the  chor- 

Fuchs.)  oidal  fissure  gives  rise  to  various  degrees  of  a 

defect  known  as  coloboma.     This  condition  may 

appear  simply  as  a  shallow  cleft  in  the  iris,  or  as  a  more  or  less  extensive 
fissure  in  the  retina  or  even  the  optic  nerve,  which  seriously  interferes  with 
vision. 

LAYERS  OF  THE  RETIKA. 

The  retina  may  be  said  to  consist  of  ten  layers,  which  from  without 
inward  are : 

1.  The  pigment  epithelium. 

2.  The  layer  of  rods  and  cones. 

3.  The  external  limiting  membrane. 

4.  The  outer  nuclear  layer. 

5.  The  fiber  layer  of  Henle. 

6.  The  outer  reticular  layer. 

7.  The  inner  nuclear  layer. 

8.  The  inner  reticular  layer. 

9.  The  ganglion  cell  layer. 
10.  The  nerve  fiber  layer. 

To  these  several  layers  an  additional  one,  the  internal  limiting  mem- 
brane, is  frequently  added.  The  first  five  of  these  layers  are  contained 
within  the  neuro-epithelial  portion  of  the  retina,  the  last  five  form  its 
cerebral  or  neural  portion. 

1.     The  pigment  epithelium  (layer  of  pigmented  cells)  consists  of 


THE  INTERNAL  COAT— THE  NERVOUS  TUNIC 


647 


a  single  layer  of  columnar  epithelial  cells  whose  bases,  of  generally  hex- 
agonal outline,  rest  upon  and  are  firmly  adherent  to  the  inner  surface 
of  the  choroid  coat,  and  from  whose  free  borders  irregular  processes 

extend  inward   between  the  ele- •  -    - 

ments  of  the  rod  and  cone  layer. 
These  epithelial  cells  have  a  finely 
granular  cytoplasm.  Their  nucle- 
us is  oval,  somewhat  flattened,  and 
placed  near  the  base  of  the  cell; 
it  is,  however,  obscured  or  even 
entirely  hidden  by  the  mass  of 
dark  pigment  granules  (fuscin) 
by  which  the  cytoplasm  of  the  cell 
is  more  or  less  completely  filled. 

The  disposition  of  the  pigment 
within  the  epithelial  cell  appar- 
ently corresponds  to,  and  is  de- 
pendent upon,  the  effect  of  light 
upon  the  retina.  In  an  eye  ex- 
posed to  the  action  of  light  at  the 
instant  of  death,  the  pigment 
granules  accumulate  in  the  irreg- 
ular processes  of  the  cells  which 
surround  the  rods  and  cones,  the 
outer  or  basal  portion  of  the  cell 
being  relatively  free  from  pig- 
ment. In  an  eye  which  is  shaded  from  the  light,  or  in  one  removed  in 
comparative  darkness,  the  pigment  has  apparently  retracted  until  it  lies 
entirely  with  the  body  of  the  cell.  Even  under 
these  conditions  the  extreme  base  of  the  cell  fre- 
quently presents  a  narrow  zone  which  is  rela- 
tively free  from  pigment.  Similar  changes  in 
the  disposition  of  the  pigment  undoubtedly  occur 
in  the  living  eye  under  the  influence  of  exposure 
to  varying  degrees  of  light. 

The  function  of  this  pigment  and  of  the  pe- 
culiar changes  in  its  disposition  is  still  somewhat 
x  500.  (After  Fuchs.)  speculative;  but  it  may>  without  doubt,  be  safely 
asserted  that  these  phenomena  are  concerned  with  the  renewal  of 
the  visual  purple  of  the  outer  segments  of  the  rods  after  the  same  has 


FIG.  546. — THE  RETINA  OF  A  CHILD'S 
EYE;  MERIDIONAL  SECTION. 

a,  nerve  fiber  layer,  the  broad  bases  of 
Miiller's  fiber  cells  show  distinctly;  b, 
blood-vessel;  c,  large  ganglion  cell  layer; 
d,  inner  reticular  layer;  e,  inner  nuclear 
layer;  /,  outer  reticular  layer,  with  a 
prominent  fiber  layer  of  Henle;  g,  outer 
nuclear  layer;  h,  layer  of  rods  and  cones; 
i,  layer  of  pigmented  epithelium;  k, 
choroid  coat.  Hematein  and  eosin. 
Photo.  X  225. 


FlG.    547. — PlGMENTEL) 

EPITHELIUM  OF  THE 
RETINA,  VIEWED  IN 
TRANSECTION, 


648 


THE  EYE 


been  bleached  by  exposure  to  light.     Possibly  these  changes  possess  a 
stimulant   action  upon   the   neuro-epithelial   elements. 

2.  The  rod  and  cone  layer  (bacillary  layer}  consists  of  a  series 
of  columnar  elements  which  are  disposed  in  a  palisade-like  manner,  and 
whose  narrow  extremities  are  embedded  in  the  surface  of  the  layer  of  pig- 
ment epithelium.  The  rod  and  cone  layer  contains  elements  of  two  dis- 
tinct types,  the  rods  and  the  cones,  specialized  receptors  of  the  rod  and 
cone  visual  cells,  and  very  similar  to  each  other  in  their  structure.  Each 


zr~ 


FIG.  548. — ISOLATED  ROD  AND  CONE  VISUAL  CELLS  OP  THE  PIG. 

a-e,  cones;  f-i,  rods;  za,  outer  segment;  zi,  inner  segment  of  the  cone,  the  latter 
consisting  of  an  ellipsoid,  ze,  and  a  more  or  less  elongated  neck,  m;  zk,  cone  nucleus; 
zf,  cone  fiber;  so,  outer,  and  si  inner  segment  of  the  rod;  sk,  rod  nucleus;  sf,  rod 
fiber.  (After  Kolliker.) 


rod  and  each  cone  visual  cell  consists  of  two  distinct  portions,  the  outer 
of  which,  alone,  lies  in  the  bacillary  layer;  the  inner  portion  is  included 
in  the  outer  nuclear  layer  of  the  retina.  The  outer  portion  is  cytoplas- 
mic,  and  its  broad  base  rests  upon  the  external  limiting  membrane;  the 
inner  portion  is  narrow,  nucleated  near  its  center,  and  extends  entirely 
through  the  outer  nuclear  layer. 

THE  EODS. — The  outer,  cytoplasmic,  or  bacillary  portion  of  each 
rod  visual  cell  consists  of  a  somewhat  thickened  spheroidal  base,  the  inner 
segment,  and  an  outer  filamentous  extremity,  the  outer  segment.  These 
two  segments  are  quite  as  distinct  in  fresh  unstained  tissue  as  in  fixed 


THE  INTEKNAL  COAT— THE  NERVOUS  TUNIC 


649 


tn  /.  e. 


and  stained  preparations,  the  distinction  being  due  to  the  fact  that  the 
inner  segment  of  each  rod,  while  finely  granular  and  easily  stained,  is 
also  singly  refractive ;  the  outer  homogeneous  segment,  on  the  other  hand, 
not  only  stains  with  difficulty  but  is 
doubly  refractive  or  anisotropic.  The 
outer,  therefore,  under  all  conditions 
appears  bright  and  lustrous  as  com- 
pared with  the  isotropic  inner  seg- 
ment. The  outer  segment  is  said  to 
be  covered  by  a  delicate  sheath  of 
neurokeratin,  and  to  consist  of  a  sub- 
stance chemically  very  similar  to 
that  of  the  myeliri  of  medullated 
nerve  fibers. 

The  outer  segment  contains  the 
visual  purple  or  rJiodopsin  which, 
during  life,  is  rapidly  bleached  by 
exposure  to  light,  and  is  as  rapidly 
renewed  through  the  agency  of  the 
pigment  epithelium. 

Both  segments,  but  especially  the 
inner,  under  favorable  conditions, 
present  slight  longitudinal  striations. 
These  striations,  when  present,  are 
most  distinct  in  the  outer  half  of  the 
inner  rod  segment  where  they  form 
the  so-called  ellipsoid;  they  are  gen- 
erally interpreted  as  due  to  linear  FIG.  549.— DIAGRAM  OF  THE  ROD 
surface  grooves  in  the  outer  segments,  S-^^B^N^ 
and  to  fibrils  in  the  ellipsoid.  The  RONS.  (Schwalbe.) 

outer  filamentous  segment  of  each  rod 

m.l.e.,  external  limiting  membrane; 

sometimes  exhibits  transverse  mark-     nj.e.;  external  nuclear  layer;  r.l.e., 
ings,    possibly    indicating    a    minute     external  reticular  (molecular)  layer; 
structure  which  is  comparable  to  a 
series  of  superposed  disks. 

The  rods  have  an  average  length  of  60  microns,  and  an  average 
diameter  of  2  microns;  of  the  entire  extent,  the  outer  cylindric  seg- 
ment and  the  inner  spheroidal  segment  contribute  approximately  equal 
portions. 

The  inner  or  nucleated  portion  of  each  rod,  the  rod  fiber,  is  found 
41 


650 


THE  EYE 


in  the  outer  nuclear  layer  and  is  continued  as. a  fine  filament,  which, 
having  penetrated  the  external  limiting  membrane,  extends  as  far  as  the 
border  line  between  the  outer  nuclear  and  outer  reticular  layers,  at  which 


FIG.  550. — A  ROD  AND  A  CONE 
VISUAL  CELL  FROM  THE  FUN- 
DUS  OF  THE  HUMAN  RE- 
TINA, OUTSIDE  THE  MACULA 
LUTE  A. 

a,  outer  segment;  b,  inner  seg- 
ment; c,  rod-  or  cone-fiber;  d, 
nucleus;  e,  rod-  or  cone-foot;  f, 
ellipsoid;  g,  myoid  (of  cone); 
h,  external  limiting  mem- 
brane. (Schafer,  Greeff.)  X 
1000. 


0.5. 


i.S 


FIG.  551. — Two  COXES   FROM  THE   HUMAN 
RETINA. 

A,  from  close  to  the  ora  serrata;  B,  from 
near  the  margin  of  the  forea  centralis.  The 
fiber  (f )  is  cut  short  beyond  the  nucleus.  Be- 
tween the  ora  and  the  fovea  cones  of  inter- 
mediate lengths  are  found,  forming  a  series 
from  A  to  B.  In  the  central  part  of  the 
fovea,  the  cones  are  still  longer  than  B,  the 
increase  being  due  mainly  to  an  elongation 
of  the  outer  segments  (os)  to  about  twice 
the  length  in  B.  (Greeff.)  X  1000. 


THE  INTERNAL  COAT— THE  NERVOUS  TUNIC 


651 


level  the  rod  filament  ends  in  a  knob-like  expansion.  Similar  knobs  may 
appear  along  its  course.  At  some  point  in  its  course  through  the  nuclear 
layer  the  rod  fiber  presents  a  nucleated  enlargement,  which,  under  some 
conditions,  shows  one  to  three  alternate  light  and  dark  transverse  stria- 
tions,  the  optical  expression  of  the  distribution  of  the  chromatin  in  the 


FIG.  552. — FROM  THE  HUMAN  RETINA. 

1,  outer  nuclear  layer;  2,  outer  reticular  layer;  3,  inner  nuclear  layer;  4,  inner 
reticular  layer;  o,  external  limiting  membrane;  b,  rod  cell  nuclei;  c,  cone  cell  nuclei; 
d,  cone  bipolars;  e,  rod  bipolars;  /,  an  exceptionally  long  process  of  a  rod  bipolar. 
Methylene  blue.  Highly  magnified.  (After  Dogiel.) 


form  of  bands.  The  nuclei  of  the  rod  fibers  are  placed  at  various  levels 
in  the  nuclear  layer,  and  collectively  occupy  nearly  its  entire  thickness. 
Its  outer  border,  however,  contains  relatively  few  rod  nuclei. 

I'm;  COXES. — The  cones  resemble  the  rods  in  structure,  but  their 
cvtoplasmic  portion  is  shorter,  the  inner  segment  of  which  is  several 
times  as  broad  (35  p.  by  7/x  ).  The  outer  anisotropic  segment  is  espe- 
cially short  and  does  not  contain  visual  purple,  while  the  isotropic  basal 
segment,  whose  fibrillated  ellipsoid  occupies  a  somewhat  greater  propor- 


652 


THE  EYE 


tion  of  its  length  than  is  the  case  with  the  homologous  rod  segment,  rests 
directly  upon,  and  may  even  project  through  the  external  limiting  mem- 
brane. The  inner  or  nucleated  portion,  therefore,  begins  as  a  broad 
nucleated  mass,  equal  in  diameter  and  continuous  with  the  bacillary  por- 
tion of  the  cone  element,  to  which  it  is  ofttimes  united  by  a  slightly  con- 
stricted neck.  In  this  inner  portion,  just  within  the  external  limiting 


MJACENT  TO  THE  CHOROiD 


TO  THE    VITREOUS 


FIG.  553. — DIAGRAMS  OF  THE  HUMAN  RETINA,  SHOWING  THE  RELATIONSHIPS  TO 
EACH  OTHER  OF  THE  RETINAL  NEURONS,  AND  THEIR  DISPOSITION  IN  THE  DIF- 
FERENT LAYERS. 

(From  Fox's  "Ophthalmology.") 

membrane,  is  the  cone  nucleus;  it  differs  from  the  rod  nucleus  in  that 
it  stains  less  deeply,  presents  no  transverse  striations,  and  frequently 
incloses  a  distinct  nucleolus.  From  its  nucleated  portion  the  cone  filter 
is  continued  as  a  rather  broad  cytoplasmic  filament  straight  inward  to  the 
border  of  the  nuclear  layer,  where  it  terminates  in  an  expanded  portion 
or  cone  foot,  from  the  flattened  inner  surface  of  which  the  fine  filaments 
penetrate  the  margin  of  the  outer  reticular  layer. 

The  outer  segments  of  both  rods  and  cones  are  embedded  in  the  cells 
of  the  pigment  layer,  whose  delicate  filamentous  processes  project  between 
the  rods  and  cones,  frequently  extending  almost  to  the  external  limiting 


THE  INTERNAL  COAT— THE  NERVOUS  TUNIC 


653 


membrane.  Both  rods  and  cones  are  hexagonal  or  nearly  circular  in 
iranscction.  The  slight,  intervals  between  the  neighboring  elements  and 
the  processes  of  the  pigment  epithelium  are  occupied  by  a  homogeneous 
fluid,  probably  a  somewhat  modified  lymph.  The  rods  far  outnumber 


FIG.  ")54. — FROM  A  MERIDIONAL  SECTION  OF  A  CHILD'S  EYE,  SHOWING  THE  LAYERS 
OF  THE  RETINA  AT  A  POINT  MIDWAY  BETWEEN  THE  MACULA  LUTEA  AND  THE 
ORA  SERRATA. 

/,  pigment  layer;  2,  bacillary  layer;  3,  external  limiting  membrane  (indistinct);  4, 
outer  nuclear  layer;  6,  outer  reticular  layer;  7,  inner  nuclear  layer;  8,  inner  reticular 
layer;  9,  ganglion  cell  layer;  10,  nerve  fiber  layer;  11,  internal  limiting  membrane; 
a,  choroid  coat.  Hematein  and  eosin.  Photo.  X  400. 


the  cones;  three  to  four  rods  generally  appear  between  two  successive 
cones.  The  total  number  of  cones  in  the  human  retina  has  been  esti- 
mated at  70,000.000:  that  of  rods  at  130,000,000. 

3.  The  external  limiting  membrane  (membrana  limitans  externa) 
consists  of  the  flattened  and  amalgamated  extremities  of  the  sustentacular 
cells  (Miiller's  fibers),  which  form  the  chief  supporting  tissue,  the  neu- 


654  THE  EYE 

roglia  element,  of  the  retina,  and  which  extend  from  the  extreme  inner 
surface  outward  to  the  external  limiting  membrane.  It  will  therefore 
he  more  convenient  to  defer  further  description  of  this  membrane  until 
the  remaining  layers  have  been  described,  and  the  Miillerian  fibers  can 
be  considered  in  their  entirety. 

4.  The  outer  nuclear  layer    (outer  granular  layer}    consists,  for 
the  most  part,  of  the  nucleated  portions  of  the  rod  and  cone  elements. 
The  outermost  zone  of  this  layer  contains  only  cone  nuclei;  the  inner 
portion,  comprising  about  three-fourths  of  its  thickness,  contains  only  rod 
nuclei.     The  former,  with  occasional  exceptions  (Stohr),  are  situated  in 
only  one  relatively  narrow  plane;  the  latter  are  distributed  at  various 
levels,  though  they  occur  more  abundantly  in  the   mid-region  of  the 
nuclear  layer.    In  addition  to  portions  of  Miiller's  fibers  which  serve  for 
the  support  of  the  nucleated  elements,  this  layer  contains  the  terminal 
filaments  of  the  distal  processes  of  some  of  the  small  bipolar  nerve  cells 
of  the  inner  nuclear  layer. 

5.  The  fiber  layer  of  Henle  is  formed  by  that  portion  of  the  cone 
fibers  which  is  internal  to  the  layer  of  rod  nuclei.    It  is  a  thin  layer  and' 
only  acquires  importance  in  the  neighborhood  of  the  macula  lutea,  where 
the  cones  are  most  abundant.     In  this  portion  of  the  retina  it  is  easily 
distinguished  from  the  outer  reticular  layer  by  the  somewhat  radial 
disposition  of  its  fibers,  the  fibers  of  the  reticular  layer  having  an  irregu- 
larly meridional  direction. 

6.  The  outer  reticular  layer    (outer  molecular  layer;  outer  plexi- 
form  layer)  presents  a  dense  tangle  of  neural  tissues  consisting  of  sup- 
porting neuroglia  fibers  and  interlacing  processes  from  the  horizontal 
and  bipolar  nerve  cells  of  the  inner  nuclear  layer.     Terminal  fibrils  from 
this  network  intermingle  in  the  fiber  layer  of  Henle  with  terminal  fibrils 
from  the  cone  feet;  more  externally  they  are  in  intimate  relation  with 
the  end  knobs  of  the  rod  fibers.    This  arrangement  permits  the  transmis- 
sion of  stimuli  from  the  neuro-epithelium  to  the  retinal  ganglion. 

7.  The  inner  nuclear  layer  (inner  granular  layer,  ganglion  retince, 
outer  ganglionic  layer)  contains  a  mass  of  nerve  cells,  together  with  the 
nucleated  portion  of  the  sustentacular  fiber  cells  of  Miiller.     The  nerve 
cells  may  be  described  as  corresponding  to  one  of  three  types,  which, 
from  the  plane  in  which  they  are  distributed  may  be  termed  the  outer, 
middle,  and  inner. 

THE  OUTER  NERVE  CELLS. — The  outer  nerve  cells  (horizontal  cells, 
basal  cells)  possess  pyramidal,  stellate,  or  flattened  cell  bodies  whose 
dendrons  are  distributed  to  the  horizontal  plexus  of  the  outer  reticular 


THE  INTEBNAL  COAT— THE  NERVOUS  TUNIC 


G55 


layer.  These  cells  vary  in  size;  the  dendritic  or  distal  processes  of  the 
smaller  cells  on  reaching  Henle's  layer  are  in  relation  with  the  terminal 
fibrils  of  the  cone  feet ;  those  from  the  larger  nerve  cells  are  in  relation 
with  the  terminal  knobs  of  the  rod  fibers.  The  axis  cylinders  or  central 
processes  from  all  these  cells  after  traveling  horizontally — viz.,  in  a  plane 
parallel  to  the  layers  of  the  retina — -for  a  greater  or  less  distance,  turn 
inward  and  pass  to  the  inner  reticular  layer,  where  they  come  into 


FIG.  555. — HORIZONTAL  CELL  FROM  THE  RETINA  OF  A  CALF. 

a,  cell  body;  6,  axon;  c,  terminal  arborizations  of  the  axon.    Golgi's  stain.     X  150. 
(After  Marenghi.) 


relation  with  the  dendrons  of  the  large  nerve  cells  of  the  ganglion  cell 
layer.  Other  processes,  mostly  from  the  smaller  cells,  terminate  in  the 
outer  reticular  layer,  probably  serving  the  purpose  of  association  neu- 
rons. 

THE  MIDDLE  TYPE. — The  nerve  cells  of  the  middle  type  are  usually 
of  bipolar  form,  and  are  the  most  abundant  elements  of  the  inner 
nuclear  layer.  The  one  set  of  their  processes  is  directed  outward  (periph- 
eralward) ;  they  pass  to  the  outer  reticular  layer  where  they  eventually 
come  into  relation  with  either  the  rod  fibers  or  the  cone  fibers.  Hence 
those  cells  which  are  in  relation  with  the  visual  rods  are  classified  as 


G56  THE  EYE 

rod  bipolars,  those  in  relation  with  the  visual  cones  as  cone  bipolars 
(Fig.  553).  The  terminal  fibrils  of  the  cone  bipolars  are  horizontally, 
those  of  the  rod  bipolars  radially,  disposed. . 

The  central  processes,  axons,  of  the  bipolar  cells  are  directed  inward 
(central ward),  and  on  entering  the  inner  reticular  layer  terminate  in 
an  end  brush  which  is  in  relation  with  the  dendritic  processes  from  the 
large  ganglion  cell  layer. 

THE  INNER  NERVE  CELL  TYPE. — The  inner  nerve  cell  type  (amac- 
rine  cells  of  Cajal)  are  large  nerve  cells  which  occupy  a  narrow  zone 
at  the  inner  margin  of  this  nuclear  layer.  These  are  large  stellate  cells 
whose  dendritic  processes  extend  into  the  inner  reticular  layer  and  take 
part  in  the  formation  of  the  dense  feltwork  of  which  that  layer  consists. 
The  course  of  the  axis-cvlinders  of  these  cells  is  still  a  matter  of  some 


FIG.  556. — Two  AMACRINE  CELLS  FROM  A  TRANSECTION  OF  THE  RETINA  OF  A  CALF. 
Golgi's  stain.     X  260.    (After  Kolliker.) 

doubt.  Ramon  y  Cajal,  believing  these  cells  to  possess  no  axon,  desig- 
nated them  'amacrine  cells'  and  subdivided  them  according  as  their  den- 
drons  were  distributed  in  either  one  of  several  horizontal  planes  (the 
number  varying  in  different  species)  or  diffusely  throughout  the  inner 
reticular  layer. 

Some  of  the  amacrine  cells,  however,  send  an  axon  in  a  horizontal 
direction  to  the  inner  reticular  layer,  and  are  also  in  relation  with  the 
terminal  arborizations  of  centrifugal  nerve  fibers  which  enter  from  the 
nerve  fiber  layer.  These  have  been  regarded  by  some  observers  as  'dis- 
located nerve  cells'  of  the  ganglion  cell  layer ;  Cajal  named  them  'associa- 
tion amacrins' 

8.  The  inner  reticular  layer  (inner  molecular  layer,  inner  plexi- 
form  layer)  is  a  densely  tangled  network  of  nerve-cell  processes,  a  neuro- 
spongium.  To  these  are  added  a  much  branched  portion  of  Miiller's 
fibers,  which  form  the  chief  supporting  tissue  of  this  layer.  The  cell  proc- 
esses entering  into  this  formation  are  derived  from  the  cells  of  the  inner 
nuclear  and  ganglion  cell  layers,  and  it  is  here  that  the  processes  of  these 
cells  interlace  so  closely  as  to  permit  the  transmission  of  impulses  from 
the  one  neuron  to  the  other.  Their  terminal  arborizations  are,  for  the 


THE  INTERNAL  COAT— THE  NERVOUS  TUNIC 


657 


most  part,  disposed  in  horizontal  planes,  though  a  few  spread  throughout 
the  entire  thickness  of  the  reticular  layer. 

9.  The  ganglion  cell  layer  (ganglion  nervi  optici,  inner  ganglionic 
layer,  layer  of  large  nerve  cells)  is  of  variable  thickness.     Its  greatest 
depth  is  in  the  region  of  the  macula  lutea,  where  it  consists  of  five  or 
six   superposed   ganglion   cells.     Toward 

the  equator  of  the  eye  it  becomes  progres- 
sively thinner,  until  near  the  ora  serrata 
its  single  layer  of  cells  only  forms  an  in- 
complete stratum. 

The  cells,  comprising  this  layer  are 
mostly  large,  stellate,  pyriform,  or  sphe- 
roidal nerve  cells,  from  whose  peripheral 
border  dendrons  pass  to  the  inner  reticu- 
lar layer,  and  from  whose  central  border 
an  axon  passes  to  the  nerve  fiber  layer  to 
eventually  become  the  axis  cylinder  of  a 
fiber  of  the  optic  nerve. 

These  cells,  though  varying  much  in 
size  and  shape,  possess  a  body  of  the  usual 
structure  with  neurofibrils  and  chromo- 
philic  granules,  and  a  pale  vesicular  nu- 
cleus with  a  distinct  chromatic  nucleolus. 
Intermingled  with  the  nerve  cells  are 
many  fine  branches  of  the  sustentacular 
cells  which  here  form  an  open-meshed 
network  within  whose  spaces  the  nerve 
cells  are  inclosed. 

10.  The  nerve  fiber  layer,  in  inti- 
mate relation  with  the  preceding,  forms 
the  innermost  of  the  retinal  zones.     It 
consists  of   naked  axis-cylinders   passing 
from  their  origin  in  the  ganglionic  layers 

to  their  immediate  destination,  the  optic  nerve.  They  are,  therefore, 
mostly  if  not  wholly  centripetal  fibers.  A  few  centrifugal  fibers  have  been 
demonstrated  in  this  layer,  but  they  would  appear  to  be  probably  vaso- 
motor  in  function,  a  few  possibly  ending  in  relation  to  the  amacrine  cells. 
The  nerve  fibers  of  this  layer  converge  from  all  portions  of  the  retina, 
follow  a  meridional  course  through  the  open  meshes  of  the  network  of 
branching  sustentacular  cells,  and  converge  toward  the  optic  papilla,  the 


FIG.  557.— A  NERVE  CELL  OP 
THE  LARGE  GANGLION  CELL 
LAYER;  FROM  THE  RETINA  OF 
A  CAT. 

n,  n,  axon;  c,  c,  collaterals. 
Golgi's  stain.  X  325.  (After 
Kolliker.) 


658 


THE  EYE 


entrance,  or  rather  the  point  of  exit,  of  the  optic  nerve.  Hence  the 
nerve  fiber  layer,  being  augmented  by  the  constant  acquisition  of  new 
axons  from  the  ganglion  cells,  becomes  pro- 
gressively thicker  toward  the  posterior  pole 
of  the  eye,  and  is  thickest  at  the  margin  of 
the  optic  papilla,  where  it  is  so  highly  de- 
veloped as  to  almost  exclude  the  other 
retinal  layers. 

The  course  of  these  non-mcdullated 
nerve  fibers  is  not  straight;  on  the  contrary, 
they  interlace  to  form  a  delicate  fibrillar 
network.  At  the  margin  of  the  papilla  op- 
tica  the  nerve  fibers  bend  outward  with  a 
sharp  curve  almost  at  right  angles  to  their 
former  course.  At  this  point  also  they  grad- 
ually acquire  a  medullary  sheath  and,  unit- 
ing into  many  bundles,  penetrate  the  nu- 
merous openings  of  the  lamina  cribrosa  of 
the  sclerotic  and  choroid  coats  to  form  the 
optic  nerve. 

THE  SUPPORTING  TISSUES  OF  THE  EETINA 


m.U. 


FIG.  558. — A  FIBER  CELL  OF 
MULLER,  OR  SUSTENTACU- 
LAR CELL,  FROM  THE  DOG'S 
RETINA. 

1,  nerve  fiber  layer;  2,  gan- 
glion cell  layer;  3,  inner  retic- 
ular  layer}  4,  inner  nuclear 
layer;  5,  outer  reticular  layer; 
6,  outer  nuclear  layer;  a,  a 
process  extending  into  the 
inner  reticular  layer;  6,  nu- 
cleus of  the  cell;  m.l.e.,  exter- 
nal limiting  membrane;  m.l.i., 
internal  limiting  membrane. 
Golgi's  stain.  Highly  mag- 
nified. (After  Cajal.) 

The  nucleus  of  the  fiber 
layer. 


These  consist  of  a  gliaform  reticulum 
distributed  throughout  the  cerebral  portion 
of  the  retina,  and  of  a  special  supporting 
tissue,  Mutter's  fibers,  which  may  also  be  re- 
garded as  glia  tissue,  though  they  are  com- 
mon to  both  the  neural  and  epithelial  por- 
tions. 

The  fibers  of  Miiller  (radial  filers; 
sustentacular  cells)  comprise  numerous  large 
glia  cells  whose  processes  begin  with  an  ex- 
panded base  at  the  inner  surface  of  the 
nerve  fiber  layer,  and  can  be  traced  all  the 
way  through  the  retina  to  the  membrana 
limitans  externa,  which  is  likewise  formed 
by  the  terminal  expansions  of  these  cells, 
cell  lies  in  the  mid-region  of  the  inner  nuclear 


THE  INTERNAL  COAT— THE  NERVOUS  TUNIC  G59 

The  expanded  and  flattened  bases  or  inner  extremities  of  these  glia 
cells  arc  so  closely  approximated  to  one  another  as  to  form  a  complete 
investment  for  the  inner  surface  of  the  retina,  which  is  known  as  the 
internal  limiting  membrane  (memlrana  limitans  inierna)  and  is  fre- 
quently classed  as  the  innermost  layer  of  the  retina.  Under  low  magnifi- 
cation it  appears  as  a  continuous  membrane,  but  under  higher  powers  it 
is  readily  resolved  into  the  broad,  conical,  basal  expansions  of  which  it 
consists.  From  these  initial  expansions  the  glia  cells  may  be  traced 
outward  through  the  nerve  fiber  and  ganglion  cell  layers  by  means  of 
the  numerous  coarse  processes  or  glia  fibers. 

The  glia  fibers  then  pass  in  a  fairly  straight  course  through  the 
inner  reticular  layer.  In  this  portion  numerous  short,  fine,  lateral  off- 
shoots from  the  main  stem  support  the  neurospongium  of  the  reticular 
layer.  Continuing  through  the  inner  nuclear  layer  the  glia  substance 
is  somewhat  thickened;  it  sends  off  fewer  but  coarser  lateral  processes, 
and  in  the  mid-region  of  this  layer  presents  an  enlargement  which  is 
almost  entirely  occupied  by  the  large  ovoid  nucleus. 

The  fiber  cell,  somewhat  narrowed,  may  then  be  traced  through  the 
outer  reticular  to  the  outer  nuclear  layer,  where  its  processes  form  a 
dense  network  about  the  nucleated  segments  of  the  rod  and  cone  visual 
cells. 

The  terminal  processes  of  the  fiber  cells  become  again  flattened,  some- 
what after  the  manner  in  which  the  internal  limiting  membrane  is 
formed,  and  are  so  closely  approximated  as  to  form  an  external  limiting 
membrane.,  a  distinctly  membranous  structure  which  derives  a  reticular 
appearance  from  being  pierced  by  each  of  the  innumerable  rod  and 
cone  elements. 

From  the  outer  surface  of  the  expanded  ends  of  the  Miillerian 
fiber  cells  which  form  the  external  limiting  membrane,  minute  fibrils 
are  continued  between  the  bases  of  the  non-nucleated  portions  of  the 
rod  and  cone  cells  to  form  shallow  sockets,  the  rod  and  cone  sockets,  into 
which  the  bacillary  portions  of  these  elements  are  fixed.  The  neuroglia 
supporting  tissue  includes  also  the  ordinary  long-  and  short-rayed  astro- 
cytes,  limited,  however,  to  the  cerebral  portion  of  the  retina. 

THE  MACULA  LUTEA 
(Yellow  Spot) 

The  macula  lutea  being  apparently  the  most  highly  developed  portion 
of  the  retina,  deserves  some  special  consideration.  The  macula  is  a  cir- 


THE  EYE 


cular  elevation  about  2  mm.  in 
diameter,  in  the  center  of  which 
is  a  marked  depression,  the  fovea 
ceniralis.  It  is  yellow  in  color, 
due  to  the  presence  of  a  pigment. 
The  elevation  results  from  an  in- 
creased thickness  of  all  the  ret- 
inal layers,  but  especially  of  the 
ganglion  cell  layer,  which  in  this 
portion  of  the  retina  is  five  or  six 
cells  deep.  The  reticular  layers 
are  also  much  thickened  in  this 
area.  In  the  bacillary  layer, 
.within  the  area  of  the  macula, 
the  cones  are  far  more  numerous 
than  elsewhere,  especially  when 
considered  in  relation  to  the  rods, 
which  are  greatly  diminished 
peripherally  and  absent  centrally. 
The  cones  of  the  macula  are  al- 
most twice  as  long  as  those  of 
the  equatorial  region  of  the  re- 
tina, the  increased  length  being 
due  to  elongation  both  of  the  in- 
ternal and  external  segments, 
but  mainly  the  latter;  they  are 
also  somewhat  more  slender,  and 
their  nuclei  may  be  placed  some 
distance  beyond  the  external  lim- 
iting membrane. 

Toward  the  fovea  central  is 
the  inner  layers  of  the  retina  be- 
come very  much  thinned,  until 
at  its  center  the  nerve  tissues  are 
merely  represented  by  scattered 
cells  of  the  inner  nuclear  and 
ganglion  cell  layers.  Rod  ele- 
ments are  not  found  in  this  area ; 
the  bacillary  layer  consists  en- 
tirely of  elongated,  slender  cones. 


THE  INTERNAL  COAT— THE  NEEVOUS  TUNIC 


661 


The  much  elongated  nuclear  portion  of  the  cones  deviates  in  a  slanting 
direction  toward  the  margin  of  the  macula,  and  the  cone  nuclei  are 
further  removed  from  the  external  limiting  membrane  than  elsewhere 
in  the  retina. 

The  pigment  of  the  epithelial  layer  is  much  diminished  and  may 
even  be  absent  at  the  fovea.  Because  of  the  diminution  in  the  number 
of  ganglion  cells  in  this  area  the  nerve  fiber  layer  is  greatly  diminished 
in  thickness  on  approaching  the  margin  of  the  fovea,  and  toward  its 
center  entirely  disappears. 

The  fovea  centralis  lies  at  the  posterior  pole  of  the  anteroposterior 
axis.  The  light  stimulus  here  meets  least  obstruction  in  passing  to  the 
neuro-epithelial  elements;  this  is  the  point  of  acutest  vision. 

Since  the  fovea  centralis  contains  no  rods,  it  lacks  the  visual  purple; 
and  since  vision  is  sharpest  at  this  point,  the  visual  purple  would  seem 
unessential  to  sight.    The 
visual  purple  is  said  to  be 
absent  in  the  eyes  of  the 
pigeon,  the  hen,  some  rep- 
tiles and  some  bats.    It  is 
supposed   to   enhance  the 
irritability  of  the  rods  in 
dim  lights. 

In  the  eyes  of  birds 
and  reptiles  the  cones  out- 
number the  rods ;  and  in 
certain  reptiles,  e.g.,  liz- 
ards, rods  are  entirely 
lacking.  In  sharks  and 
rays,  most  nocturnal  ani- 
mals, and  the  owl,  cones 
are  either  absent  or  few  in 
number  or  rudimentary  in 
structure.  According  to 
the  view  of  Kreis  (1895) 
the  cones  function  in  the 
perception  of  color,  the  rods  are  sensitive  only  to  light  and  darkness.  In 
color  blindness  the  cones  are  defective;  in  night-blindness  the  rods  are 
affected. 

Development  of  Rods  and  Cones.— The  rods  and  cones  arise  and  by 
an  essentially  identical  mode  of  differentiation  from  apparently  similar  em- 
bryonic cells.  A  protoplasmic  bud  is  pushed  beyond  the  external  limiting 
membrane  towards  the  layer  of  pigmented  cells.  The  cone  bud  is  from 


FIG.  560. — DEVELOPING  ROD  AND  CONE  VISUAL 
CELLS,  FROM  THE  RETINA  OF  A  345  MM.  (6  MOS.) 
HUMAN  FETUS. 

M,  diplosome  in  a  Muller's  fiber  at  the  level  of 
the  external  limiting  membrane;  C,  diplosome  in  a 
cone  cell;  F,  fiber  growing  out  from  the  cone  diplo- 
some; R,  diplosome  in  a  rod  visual  cell.  (Seefelder.) 
X  1000. 


662  THE  EYE 

four  to  five  times  as  stout  as  that  of  the  rod  cell.  These  processes  carry 
apically  a  diplosome,  surrounded  by  a  lighter  cytoplasmic  halo.  From  each 
member  of  the  diplosome  a  fiber-process  grows  out,  the  one  passing  towards 
the  elongating  distal,  the  other  towards  the  proximal,  pole  of  the  cell.  The 
distal  process  thus  becomes  enveloped  by  an  extension  of  the  cell  cytoplasm, 
the  two  constituents,  fiber  and  investing  cytoplasm,  uniting  in  the  forma- 


V/ 


I 


FIG.  561. — Two  EARLY  STAGES  IN  THE  DEVELOPMENT  OF  THE  ROD  AND  CONE 
VISUAL  CELLS  IN  THE  CHICK. 

A,  from  12-day  embryo,  showing  the  visual  cell  buds  containing  mitochondria; 
L.e.,  external  limiting  membrane;  C.V.,  visual  cell;  R.e.,  external  reticular  layer; 
C.p.,  bipolar  cells;  B,  from  1-day-old  chick,  showing  two  complete  rods  and  one 
cone,  both  elements  containing  a  large  lipoid  spherule  (G)  and  mitochondria.  The 
cone  contains  an  ellipsoid  (E);  seg.  int.,  internal  segment;  seg.  ext.,  external  segment. 
(Leplat.)  X  about  2000. 

tion  of  the  outer  segment  of  the  rods  and  cones.  Seefelder  ("Atlas  zum 
Entwickslungsgeschichte  des  Menschlichen  Auges,"  Leipzig,  1914)  has  re- 
cently confirmed  the  essential  points  in  the  earlier  descriptions  of  rod  and 
cone  differentiation  by  Leboucq  (1909)  and  by  Magiott  (1910).  Leplat 
(Anat.  Anz.,  45,  8,  1913)  has  investigated  the  role  of  the  mitochondria  in 
connection  with  this  process.  He  describes  the  migration  of  the  'plasto- 
somes'  into  the  external  segment  where  they  become  chemically  altered 
and  disappear  as  such  in  their  contribution  to  the  homogeneous  cytoplasmic 
sheath  of  the  centrosomal  filament  of  the  external  segment.  Leplat  inclines 
to  regard  the  transverse  striation  of  this  segment  and  its  cleavage  int® 


THE  INTERNAL  COAT— THE  NERVOUS  TUNIC 


663 


discs  by  maceration  as  the  expression  of  its  mode  of  construction  from 
mitochondria.  It  remains  uncertain  whether  the  longitudinal  fibrillation 
of  the  internal  segments  is  likewise  the  probable  result  of  an  arrangement 
of  mitochondria  in  the  developing  cell;  the  complete  history  of  these  mito- 
chondria has  not  yet  been  traced. 

The  Inversion  of  the  Retina. — The  receptive  cells  of  the  vertebrate 
retina  exhibit,  in  contrast  to  all  other  neuro-epithelial  cells,  a  reversed 
polarity  with  respect  to  the  source  of  their  special  stimulus,  the  ether 
waves;  the  transmitting  end  of  the  cells  is  nearer  the  source  of  the  light 
than  the  percipient  end.  The  human  retina  is  appropriately  described  as 


Neural  ectoderm 
Neural  canal  (forebrain) 
Epidermal  ectoderm 

Optic  cup 
Optic  stalk 

Rathke's  pouch 
Buccal  cavity 


Infun  ibulum 


FIG.   562. — DIAGRAM   ILLUSTRATING   BALFOUR'S  THEORY  TO   ACCOUNT  FOR  THE 
INVERSION  OF  THE  VISUAL  CELLS  OF  THE  VERTEBRATE  RETINA. 

Transverse  section  through  the  head  of  a  hypothetical  vertebrate  embryo,  to 
show  the  morphological  relations  of  the  surfaces  of  the  ectoderm  of  the  integument, 
the  neural  tube,  and  the  forming  retina.  In  each  of  these  situations  a  single  sense 
cell  is  indicated.  (After  Parker,  Amer.  Nat.,  42,  501,  1908.) 


an  inverted  sense-organ.  The  most  plausible  theory  yet  proposed  in  ex- 
planation of  this  inversion  of  the  visual  cells  seems  to  be  the  one  outlined 
by  Balfour  (1881),  expressed  in  terms  of  the  ancestral  history  of  the  verte- 
brate eye.  (Among  the  invertebrates  an  inverted  retina  is  known  only  in 
certain  mollusca,  e.g.,  Pecten,  and  in  certain  spiders  and  the  scorpion.) 
'According  to  this  view  the  vertebrate  retina  originated  on  the  outer  sur- 
face of  the  ancestral  vertebrate  in  much  the  way  that  the  eyes  of  many 
invertebrates  have  been  produced.  The  primitive  retinas  thus  formed 
were  implanted  in  that  portion  of  the  surface  of  the  animal  from  which 
the  central  nervous  system  was  destined  to  develop,  and  when  this  was 
infolded  these  retinas  were  carried  in  with  it  and  came  thus  to  be  involved 
in  the  central  organ.  If  the  morphological  position  of  a  sensory  cell,  such 
as  may  have  existed  in  the  primitive  external  retina,  is  supposed  to  have 
been  thus  retained  as  this  organ  was  carried  from  its  superficial  location 
into  the  central  nervous  system  and  out  again  almost  to  the  external  sur- 


664 


THE  EYE 


face,  the  resulting  retina  would  be  composed  of  inverted  elements  (Fig. 
562).  Thus  this  theory  at  once  offers  an  explanation  for  the  two  most 
striking  features  of  the  vertebrate  retina,  namely,  its  formation  as  an 
apparent  outgrowth  from  the  central  nervous  system  and  the  inverted  con- 
dition of  its  receptive  cells'  (Parker).  The  difficulties  of  this  theory  are 

discussed,  and  an  alternative 
theory,  based  upon  the  direc- 
tion eyes  of  Amphioxus,  is 
presented  by  G.  H.  Parker 
(Amer.  Nat.,  42,  501,  1908). 


THE  OPTIC  NERVE 

The  optic  nerve  is  a 
large  nerve  trunk,  com- 
posed, like  the  white  mat- 
ter of  the  brain  of  which  it 
is  an  ontogenetic  portion, 
of  medullated  nerve  fibers 
without  a  neurolemma,  sup- 
ported by  a  neurogliar  net- 
work containing  long-rayed 
astrocytes.  It  receives  an 
investing  sheath  from  each 
of  the  cerebral  membranes, 
septa  from  the  pia  mater 
enveloping  the  several  funi- 
culi.  These  sheaths  are 
continued  as  far  forward 
as  the  eyeball,  at  which 
point  they  become  contin- 
uous with  the  sclera. 
Though  the  choroid  corre- 
sponds to  the  pia  mater,  the 
two  are  not  apparently  in 
direct  continuity. 

Lying  in  the  axis  of  the 
nerve,  the  arteria  centralis 
relince  with  its  accompany- 
ing vein  enters  the  eye  and 
appears  on  the  inner  sur- 


THE  OCULAR  CONTENTS  665 

face  of  the  retina  at  the  porus  options  (physiologic  excavation;  optic 
disk)  in  the  center  of  the  optic  papilla.  Here  it  divides,  its  two  branches 
at  first  pursuing  a  meridional  course  between  the  hyaloid  membrane  and 
the  retinal  surface;  soon  they  pierce  the  latter  to  supply  the  cerebral 
portion  of  the  retina.  No  vessels  penetrate  the  neuro-epithelial  portion 
of  the  retinal  layers ;  these  are  nourished  by  the  choroid.  The  vena  cen- 
tralis  retince  pursues  a  course  exactly  similar  to  that  of  the  artery. 

THE  ORA  SERRATA 

At  the  ora  serrata  (Fig.  538)  the  typical  layers  of  the  retina,  already 
mm-li  thinned,  abruptly  cease.  The  first  elements  to  disappear  are  the 
rods  and  cones ;  the  cones,  which  become  much  shorter,  practically  lacking 
the  outer  segment,  extend  farther  toward  the  ora  than  the  rods.  The 
remaining  layers  are  continued  forward  only  as  the  double  layer  of 
epithelial  cells  belonging  to  the  pars  ciliaris  retinae,  the  inner  stratum 
of  which  appears  to  be  analogous  to  and  continuous  with  the  cerebral 
portion  of  the  retina,  apparently  the  sustentacular  cells ;  while  the  outer, 
deeply  pigmented  layer  apparently  represents  the  pigmented  layer  of  the 
retina.  For  some  distance  toward  the  ora  serrata,  the  retina  becomes 
modified  by  the  presence  of  large  vacuoles,  probably  lymph  spaces. 


THE  OCULAR  CONTENTS 

Within  the  ocular  globe,  whose  walls  are  formed  by  the  three  coats 
of  the  eye,  are  certain  structures  which  may  be  collectively  considered  as 
its  contents.  They  are: 

1.  The  aqueous  humor. 

2.  The  crystalline  lens. 

3.  The  vitreous  humor. 

4.  The  hyaloid  membrane. 

5.  The  suspensory  ligament. 

THE  AQUEOUS  HUMOR 

The  aqueous  humor  is  a  fluid,  closely  allied  to  lymph,  which  occupies 
the  anterior  and  posterior  chambers  of  the  eye.     Microscopically  it  is 
structureless.     Occasional   leukocytes,   migrants   from   adjacent   lymph 
channels,  may  be  encountered. 
42 


666  THE  EYE 

THE  CRYSTALLINE  LENS 

The  crystalline  lens  with  its  suspensory  ligament  forms  a  sort  ol 
diaphragm  which  separates  the  ocular  cavity  into  two  compartments, 
of  which  the  anterior  is  occupied  by  the  aqueous  humor,  the  posterior 
by  the  vitreous  humor. 

The  lens  is  a  biconvex  transparent  body  having  a  somewhat  greater 
convexity  on  its  posterior  than  on  its  anterior  surface;  its  curvature 
is  greater  at  its  margin  than  toward  its  center.  It  has  a  transverse 
diameter  of  from  8  mm.  to  9  mm.,  and  an  anteroposterior  diameter  of 
from  3.5  mm.  to  4  mm.  according  to  the  degree  of  accommodation.  It 
consists  of  a  capsule,  epithelium,  and  a  substantia  lentis. 

The  capsule  of  the  lens  is  a  homogeneous  membrane  which  covers 
its  entire  surface  and  receives  the  attachment  of  the  suspensory  liga- 
ment. It  presents  faint  meridional  striations  and  may  sometimes  be 
separated  into  several  lamella?  (Berger,  1893)  ;  this  lamellation  may  be 
purely  artificial,  but  appears  to  be  somewhat  dependent  upon  the  attach- 
ment of  the  fibers  of  the  suspensory  ligament  to  the  surface  of  the 
lenticular  capsule. 

The  capsule  is  about  twice  as  thick  over  the  anterior  as  over  the 
posterior  surface  of  the  lens.  On  the  former  surface  it  is  in  relation 
with  the  lenticular  epithelium,  but  on  the  posterior  surface  the  capsule 
rests  directly  upon  the  substantia  lentis.  The  anterior  surface  of  the 
capsule  is  in  gentle  contact  with  the  free  margin  of  the  iris. 

The  lenticular  epithelium  consists  of  a  single  layer  of  cells  which 
covers  the  entire  anterior  convexity  of  tKe  lens,  extending  as  far  back  as 
its  equator.  The  height  of  these  cells  varies  with  the  age  of  the  indi- 
vidual. In  fetal  life  they  are  distinctly  columnar,  in  youth  short  colum- 
nar or  cuboidal,  in  adult  life  low  cuboidal  or  flattened.  Toward  the  mar- 
gin of  the  lens  the  epithelial  cells  become  progressively  lengthened,  and 
at  its  equator  are  transformed  directly  into  the  fibers  of  the  lenticular 
substance.  This  definitive  structure  of  the  lens  recalls  its  manner  of 
development  from  the  original  lens  vesicle;  the  hollow  vesicle  becomes 
solid  by  the  elongation  of  the  cells  of  the  posterior  wall. 

The  substantia  lentis  is,  therefore,  the  product  of  the  epithelium 
of  the  lens,  whose  cells  become  greatly  elongated  to  form  slender  hexag- 
onal prisms,  known  as  the  lens  fibers.  When  it  is  first  formed  each 
prism  exhibits  a  nucleus  which  persists  for  some  time,  but  gradually 
disappears  as  in  the  process  of  growth  the  older  fibers  become  farther 
and  farther  removed  from  their  source  of  nutrition,  the  lymph  and  the 


THE  OCULAE  CONTENTS 


667 


aqueous  humor  in  which  the  surface  of  the  lens  is  bathed.  This  change 
is  accompanied  by  a  hardening  or  cornification  and  slight  shrinkage 
of  the  lens  fibers,  so  that  those  prisms  which  come  to  occupy  the  center 
of  the  lens  form  a  dense,  hard  mass  of  non-nucleated  fibrous  cells  with 
faintly  serrated  margins;  the  peripheral  fibers  retain  their  smooth  edges 
and  their  nuclei,  and  form  a  protoplasmic  mass  of  much  softer  con- 
sistency. The  hardened  central  mass  is 
the  so-called  nucleus  of  the  lens.  Any 
opacity  of  the  lens  or  its  capsule  is  known 
as  a  cataract. 

The  nuclei  of  the  lens  fibers  remain  in 
the  neighborhood  of  the  equator,  where 
they  are  first  formed,  and  are  thus  con- 
tained within  a  narrow,  Superficial,  equa- 
torial zone,  the  nuclear  zone. 

Each  lens  fiber  is  disposed  along  a 
meridian  of  the  lens,  and  extends  from 
its  anterior  to  its  posterior  hemisphere; 
the  fibers  are  so  arranged  that  they  abut 
upon  one  another,  end  to  end,  along  V- 
shaped  lines  which  radiate  from  either 
pole.  This  union  is  often  quite  firm,  and 
thus  are  formed  long  fibrous  bands  which 
can  be  traced  from  the  anterior  to  the 
posterior  hemispheres  of  the  lens.  These 
bands  are  distributed  in  a  peculiar  man- 
ner. Near  each  pole  along  the  line  of 
abutment,  the  band  may  be  said  to  bend 
upon  itself  with  a  sharp  curve — making 
an  angle  of  about  60  degrees — whose  convexity  is  directed  toward  the  pole, 
the  parallel  fibers  being  so  arranged  as  to  form  a  sector  whose  apex  is 
also  directed  toward  the  pole.  The  corresponding  sectors  of  opposite 
poles  overlap  one  another  so  that  the  fibrous  bands  are  continued  from 
one  side  of  one  polar  mass  to  the  reverse  side  of  the  overlapping  sector 
and  so  back,  on  the  farther  side,  to  the  adjacent  sector  of  the  former 
hemisphere.  By  teasing,  fibrous  bands  can  sometimes  be  traced  suc- 
cessively through  all  of  the  polar  sectors  and  thus  back  to  a  sector  be- 
neath that  from  which  the  start  was  made.  Obviously  no  individual 
lens  fiber  is  of  sufficient  length  to  extend  from  pole  to  pole  of  the 
lens. 


FIG.  564. — LENS  FIBERS. 

1,  in  profile,  from  the  crystal- 
line lens  of  the  ox's  eye;  2,  in 
tr  ansec  tion,  from  the  human  cry  s- 
talline  lens.  X  350.  (After 
Kolliker.) 


668 


THE  EYE 


The  polar  figures  formed  by  the  lines  of  terminal  union  of  the  lens 
fibers  are  known  as  lens  stars;  these  are  at  first  three-rayed,  but  later 
become  six-  and  even  nine-rayed. 

During  the  earlier  stages  of  the  development  the  lens  is  invested 


FIG.  565. — THE  NUCLEAR  ZONE  AT  THE  MARGIN  OF  THE  CRYSTALLINE  LENS  OF  A 
CHILD'S  EYE,  SHOWING  THE  TRANSITION  OF  THE  LENS  EPITHELIUM  TO  THE  LENS 
FIBERS  AND  THE  ATTACHMENT  OF  THE  SUSPENSORY  LIGAMENT. 

a,  lens  fibers;  b,  lenticular  epithelium;  c,  capsule  of  the  lens;  d,  suspensory  liga- 
ment.   Hematein  and  eosin.     X  273. 


by  a  delicate  vascular  membrane,  the  tunica  vasculosa  lentis  (designated 
pupillary  membrane  in  front),  supplied  by  the  hyaloid  artery  continued 
from  the  central  artery  of  the  retina.  This  tunic  normally  disappears 
before  birth;  its  atypical  persistence  in  whole  or  in  part  seriously  inter- 
feres with  vision. 


THE  OCULAE  CONTENTS  669 

THE  VITREOUS  HUMOR 

The  vitreous  humor  (vitreous  body)  is  a  soft  jelly-like  mass  which 
fills  the  entire  cavity  of  the  eye  behind  the  line  of  the  ora  serrata  and 
crystalline  lens.  About  98  per  cent,  of  its  composition  is  water.  It  is 
completely  invested  by  the  hyaloid  membrane.  Its  anterior  excavation 
which  holds  the  posterior  convexity  of  the  lens  is  known  as  the  hyaloid 
or  patellar  fossa.  The  vitreous  humor  appears  to  be  a  peculiarly  deli- 
cate form  of  very  loose  gelatinous  connective  tissue  whose  scanty  fibers 
present  a  somewhat  concentrically  lamellated  arrangement  and  are  so 
very  delicate  as  to  be  recognized  under  ordinary  conditions  only  with  the 
greatest  difficulty. 

Occasionally  stellate  and  fusiform  cells,  remarkable  for  their  large 
vacuoles  and  varicose  processes,  have  been  demonstrated  in  small  num- 
bers within  the  vitreous  body.  Small  rounded  cells  somewhat  resembling 
leukocytes  are  also  found,  but  for  the  most  part  they  are  flattened  against 
the  hyaloid  membrane;  they  occur  in  very  limited  numbers. 

These  various  cells,  as  well  as  occasional  filamentous  remnants  of 
the  original  mesenchymal  constituents  of  the  vitreous  humor,  may  cast 
shadows  upon  the  retina  within  the  visual  field.  Such  shadows,  called 
miLScce  volitantes,  on  account  of  their  'flitting*  motion  when  the  eyes 
are  moved,  are  seen  when  looking  at  a  bright  light,  or  frequently  in 
looking  through  the  microscope.  In  advanced  age  crystals  may  form 
in  the  vitreous  which  are  observed  to  settle  to  the  bottom  of  the  eye 
when  the  eyes  are  held  still. 

THE  HYALOID  MEMBRANE 

The  hyaloid  membrane  is  a  very  thin  structure  which  surrounds  the 
vitreous  humor  and  unites  it  to  the  inner  surface  of  the  retina  and  the 
crystalline  lens.  It  consists  of  delicate  glassy  fibers  so  disposed  as  to 
form  an  extremely  thin  reticular  membrane.  It  passes  forward  over  the 
inner  surface  of  the  retina,  to  which  it  is  loosely  united,  until  at  the  ora 
serrata  its  fibers  leave  the  retinal  surface  and  pass  inward  to  the  margin 
of  the  lens  to  become  inserted  into  the  lenticular  capsule. 

THE  SUSPENSORY  LIGAMENT 
(Zonula  Clliaris) 

Certain  fibers  from  the  hyaloid  membrane  pass  forward  from  the 
ora  serrata  and  are  firmly  adherent  to  the  ciliary  processes,  or  become 


670  THE  EYE 

attached  in  the  grooves  between  the  processes.  From  the  sides  of  these 
processes  fibers  diverge  at  frequent  intervals  and  pass  to  the  margin 
of  the  lens,  where  they  are  attached  on  either  side  of  the  equator,  spread- 
ing over  a  zone  which  is  somewhat  narrower  posteriorly  than  anteriorly. 
These  fibers  form  the  suspensory  ligament  of  the  crystalline  lens  (Figs. 
543  and  565).  They  occupy  an  annular  zone  which  is  included  between 
the  ciliary  processes  and  the  margin  of  the  lens,  and  which  is  known 
as  the  zonula  ciliaris  (of  Zinn). 

The  glassy  fibers  of  this  ligament  take  origin  from  the  sides  of  the 
ciliary  processes  along  which  they  are  firmly  attached,  becoming  free  only 
near  the  apices  of  these  processes.  They  pass  thence  to  the  margin  of 
the  lens  and  spread  out  upon  the  surface  of  the  capsule  to  which  they 
are  intimately  adherent.  The  fibers  arising  more  posteriorly  are  said 
to  be  attached  to  the  lens  anteriorly  to  the  equator,  those  arising  from 
the  more  anterior  portions  of  the  ciliary  processes  becoming  attached 
posteriorly  to  the  equator  of  the  lens. 

The  most  anterior  of  these  fibers  form  a  somewhat  plicated  but  in- 
complete membrane  which  serves  as  the  anterior  boundary  of  an  annular 
series  of  connecting  lymphatic  spaces  collectively  forming  the  spatia 
zonularis  (canals  of  Petit).  This  irregularly  sacculated,  annular  canal 
is  bounded  posteriorly  by  the  hyaloid  membrane,  anteriorly  by  the  in- 
complete membranous  wall  of  the  posterior  chamber  through  which  the 
aqueous  humor  readily  diffuses,  internally  by  the  margin  of  the  crystal- 
line lens,  and  antexo-externally  by  the  ciliary  processes.  Besides  sup- 
porting the  lens,  the  suspensory  ligament  assists  in  the  accommodation 
of  the  lens  to  far  and  near  vision,  a  process  involving  a  change  of  con- 
vexity, and  dependent  upon  the  activity  of  the  ciliary  muscle. 


BLOOD-VESSELS   OF  THE  EYE 

The  circulation  of  blood  in  the  globe  of  the  eye  is  maintained  through 
four  sets  of  vessels: 

1.  The  arteria  and  vena  centralis  retinae. 

2.  The  short  ciliary  arteries  and  venaa  vorticosas. 

3.  The  long  ciliary  arteries. 

4.  The  anterior  ciliary  arteries  and  veins. 

1.  The  arteria  centralis,  destined  for  the  supply  of  the  retina,  en- 
ters the  optic  nerve  about  midway  between  the  optic  commissure  and 
the  ocular  globe,  and  arriving  at  the  center  of  the  nerve  runs  in  its  axis 


BLOOD-VESSELS  OF  THE  EYE 


671 


to  the  papilla  optica, 
at  w  h  i  c  li  point  it 
divides  into  two 
branches,  an  inferior 
and  a  superior  branch, 
which,  by  rapid  dicho- 
tomous  division,  radi- 
ate from  the  optic 
papilla  to  all  parts  of 
the  retinal  surface, 
thereby  forming  a 
plexus  of  small  ar- 
teries within  the 
nerve  fiber  and  gan- 
glion cell  layers. 
From  this  plexus  ca- 
pillaries are  distrib- 
uted to  all  the  cere- 
bral layers  of  the  re- 
tina. No  blood-vessels 
are  found  within  the 
neuro-epithelial  lay- 
ers. The  retinal  ar- 
teries, like  those  of 
the  brain,  do  not  anas- 
tomose  with  one  an- 
other;  they  are  ter- 
minal  arteries. 

The  retinal  veins 
follow  a  course  exact- 
ly similar  to  that  of 

FIG.  566. — SCHEMATIC  REPRESENTATION  OF  THE  INTRINSIC   BLOOD-VESSELS  OF 
THE  EYE. 

Arteries  in  outline,  veins  in  solid  black.  A,  choroid;  a,  central  artery,  and  alt  vein 
of  the  retina;  B,  conjunctiva;  b,  retinal  arteries;  6,,  retinal  veins;  c,  c,  short  ciliary 
arteries;  d,  long  ciliary  artery;  e,  e,,  anterior  ciliary  arteries  and  veins;  /,  chorio- 
capillaris;  g,  capillaries  of  the  ciliary  body;  H,  cornea;  h,  circulus  major  of  the 
iridal  arteries;  i,  arteries,  and  i\,  veins  of  the  iris;  k,  circulus  minor  of  the  iridal 
arteries;  L,  crystalline  lens;  I,  venae  vorticosse;  m,  anastomosis  of  ciliary  and  an- 
terior ciliary  veins;  N,  retina;  n,  canal  of  Schlemm;  O,  optic  nerve;  o,  posterior 
conjunctiva!  artery,  and  o\t  vein;  p,  anterior  conjunctival  vessels;  ?,  vascular  loops 
at  the  margin  of  the  cornea;  R,  internal  rectus  muscle;  S,  sheath  of  the  optic  nerve; 
Sc,  sclera.  (After  Leber.) 


672  THE  EYE 

the  arteries;  they  converge  to  form  a  single  efferent  vessel,  the  vena  cen- 
tralis  retinae.  The  retinal  veins  are  peculiar  in  that  their  walls  contain 
no  muscle.  The  optic  nerve  is  supplied  with  small  branches  from  the 
arteria  and  vena  ceutralis  retinae  in  their  passage  through  its  substance. 
In  the  fetus  a  small  branch,  the  hyaloid  artery,  apparently  the 
direct  continuation  of  the  arteria  centralis  retinae,  passes  forward  through 
the  vitreous  humor  to  the  posterior  surface  of  the  lens,  whence  capillary 
vessels  pass  around  the  margin  of  the  lens  and  are  connected  with  the 
anterior  ciliary  vessels  at  the  margin  of  the  iris.  The  hyaloid  artery 
supplies  blood  to  the  fetal  tunica  vasculosa  lentis  for  the  nutrition  of 
the  developing  lens.  Before  birth  these  vessels  disappear;  the  hyaloid 
artery  remains  for  a  time  as  a  delicate  fibrous  strand,  occupying  the 
persistent  canalis  hyaloideus  or  canal  of  Stilling,,  which  lies  almost  in 
the  visual  axis  and  extends  from  the  papilla  optica  to  the  posterior 
surface  of  the  lens.  The  hyaloid  canal  (also  called  the  canal  of  Cloquet) 
establishes  a  channel  between  the  aqueous  humor  and  the  lymphatic- 
spaces  of  the  retina.  In  adult  life  both  the  vitreous  humor  and  the 
crystalline  lens  are  bloodless  tissues. 

2.  The  short  ciliary  arteries,  twelve  to  fifteen  in  number,  enter 
the  globe  of  the  eye  in  a  circle  (circle  of  Zinn)  which  surrounds  the 
optic  nerve.    They  supply  branches  to  the  meningeal  sheaths  of  the  optic 
nerve  and  to  the  sclera,  their  main  stems  penetrating  this  coat  to  enter 
the  choroid.    Here  they  subdivide  to  form  the  plexus  of  arteries  in  the 
lamina  vasculosa  from  which  the  vessels   of  the  choriocapillaris  are 
supplied.     The  capillaries  of  the  last-named  layer  unite  to  form  small 
venous  radicals  which  converge  toward  the  equator  of  the  eye,  where  they 
unite  in  a  whorl-like  manner  to  form  the  four  or  five  vence  vorticosce, 
which  pass  obliquely  backward  through  the  sclera,  receiving  additional 
branches  from  this  coat,  and  finally  emerging  from  the  eye  to  empty 
into  the  ophthalmic  vein. 

The  vessels  of  the  choroid  communicate  posteriorly  with  those  of 
the  optic  nerve,  and  anteriorly,  by  a  free  anastomosis,  with  those  of 
the  ciliary  processes. 

3.  The  long  ciliary  arteries,  two  in  number,  enter  peripherally  at 
the  circle  of  Zinn  on  either  side  of  the  optic  nerve,  and  pass  horizontally 
forward  upon  the  outer  surface  of  the  choroid  to  the  ciliary  muscle. 
Near  the  base  of  the  iris  they  divide,  and  by  anastomosis  with  each 
other  and  with  the  anterior  ciliary  arteries  form  a  vascular  circle,  the 
drculus  major,  about  the  base  of  the  iris. 

Prom   this   circle  recurrent   branches  supply  the   ciliary  body  and 


THE  LYMPHATIC  SYSTEMS  OF  THE  EYE  673 

anastomose  with  the  vessels  of  the  choroid;  other  branches  pass  into 
the  iris  and,  converging  toward  the  visual  axis  form,  just  outside  the 
pupillary  margin,  a  second  circle  of  anastomosis,  the  circulus  minor. 

The  veins  of  the  iris  and  ciliary  body  follow  closely  the  distribution 
of  the  arteries,  the  greater  portion  of  their  blood  returning  through 
the  veins  of  the  choroid  and  the  vena3  vorticose.  Some,  however,  is 
returned  by  means  of  anastomoses  with  the  anterior  ciliary  veins. 

4.  The  anterior  ciliary  arteries,  derived  from  the  muscular  and 
lacrimal  branches  of  the  ophthalmic,  distribute  branches  to  the  con- 
junctiva and  sclera,  and  within  the  latter  membrane,  about  2  mm.  outside 
of  the  corneal  margin,  pass  to  the  circulus  iridis  major  and  partially 
supply  the  iris  and  ciliary  body  as  already  described. 

The  anterior  ciliary  veins  follow  the  course  of  the  corresponding 
arteries.  They  empty  into  the  vessels  of  the  ocular  conjunctiva. 


THE  LYMPHATIC  SYSTEMS  OF  THE  EYE 

The  lymphatic  systems  of  the  eye  include  very  few  true  lymphatic 
vessels,  but  consist  rather  of  a  series  of  channels  which  may  be  arbitrarily 
considered  as  an  anterior  and  a  posterior  set  of  intercommunicating 
spaces.  The  former  set  includes  the  lymphatic  spaces  of  the  cornea, 
the  spaces  of  Fontana,  the  anterior  and  posterior  chambers,  the  lymphatic 
clefts  of  the  ciliary  muscle  and  iris,  and  the  zonular  spaces  or  canals  of 
Petit.  The  posterior  set  includes  the  subdural  and  subarachnoid  spaces 
in  the  sheath  of  the  optic  nerve,  the  capsule  of  Tenon,  the  lymphatic 
spaces  of  the  lamina  suprachoroidea,  the  perivascular  spaces  of  the 
choroid  and  retina,  the  irregular  clefts  between  the  pigmentary  and 
bacillary  layers  of  the  retina,  the  similar  clefts  of  the  ganglion  cell 
layer,  the  lymphatic  spaces  of  the  hyaloid  membrane,  the  hyaloid  canal, 
and  the  interstices  of  the  vitreous  humor. 

These  two  sets  of  lymphatic  channels  communicate  with  each  other 
by  means  of  the  perivascular  spaces  of  the  two  outer  tunics,  as  well  as 
through  that  portion  of  the  hyaloid  membrane  which  forms  the  posterior; 
wall  of  the  spatia  zonularis,  through  the  clefts  of  which  and  the  hyaloid 
canal  the  lymph  of  the  vitreous  body  communicates  freely  with  the 
aqueous  humor  of  the  spatia  zonularis  and  posterior  chamber.  Conse- 
quently, if  the  cornea  be  penetrated  either  accidentally  or  otherwise, 
and  the  anterior  and  posterior  chambers  be  emptied,  their  aqueous 
humor  is  rapidly  replaced,  not  only  from  the  adjacent  spaces  of  the 


674  THE  EYE 

anterior  set  of  lymphatic   vessels,  but  from  the  vitreous  humor   and 
posterior  set  as  well. 

It  is  also  important  to  note  that  the  posterior  set  of  lymphatic 
spaces  is  directly  connected  through  the  meningeal  sheaths  of  the  optic 
nerve  with  the  subdural  and  subarachnoid  spaces  of  the  cerebral 
meninges. 

THE  NERVES  OF  THE  EYE 

The  nerves  of  the  eye,  in  addition  to  the  optic,  are  the  long  and 
short  ciliary  branches  of  the  ophthalmic  nerve.  The  former,  two  or 
three  in  number,  and  the  latter,  six  to  ten,  after  supplying  a  vasomotor 
branch  to  the  artcria  centralis  retina3,  pierce  the  sclera  in  company  with 
the  corresponding  ciliary  arteries  and  pass  meridionally  forward  on  the 
inner  surface  of  the  sclera,  supplying  branches  to  this  tunic  and  to  the 
vessels,  of  the  choroid,  and  finally  reaching  the  ciliary  muscle,  where 
their  branches  form  an  annular  plexus  containing  a  few  ganglion  cells. 

From  this  plexus  fibrils  are  supplied  to  the  blood-vessels  and  mus- 
cular tissues  of  the  ciliary  body  and  iris,  and  to  the  cornea.  The  corneal 
branches  pass  to  the  annular  plexus  at  the  sclerocorneal  junction,  whence 
they  are  distributed  to  the  corneal  tissues,  as  already  described  (page 
633). 


APPENDAGES   OF   THE   EYE 

The  appendages  of  the  eye  include  the  eyelids,  conjunctiva,  and 
lacrimal  glands. 

THE  EYELIDS 

The  eyelids  are  developed  in  the  embryo  through  an  imagination  of 
the  skin,  which,  leaving  a  slit-like  aperture  (the  palpebral  fissure) 
between  its  involuted  margins,  covers  the  inner  surface  of  the  lid  to 
form  the  palpebral  conjunctiva,  and  is  reflected  over  the  globe  of  the 
eye  as  the  ocular  conjunctiva  and  anterior  corneal  epi^Jielium. 

The  lids,  therefore,  may  be  said  to  consist  of  two  membranous  por- 
tions, the  cutaneous  (outer  or  anterior)  and  the  conjunctival  (inner  or 
posterior).  Between  these  two  portions  the  orbicularis  palpebrarum 
forms  a  septum  of  striated  muscle  fibers. 

The  cutaneous  portion  of  the  eyelid  differs  from  other  portions 


APPENDAGES  OF  THE  EYE 


675 


of  the  skin  only  in  that  its  subcutaneous  tissue  contains  no  fat.  The 
derma  is  loosely  connected  with  the  muscle  by  a  wide-meshed  areolar 
tissue.  Fine  hairs  are  distributed  over  the  cutaneous  surface,  their 
follicles  extending  well  down  through  the  derma.  Small  sebaceous 


FIG.  567. — VERTICAL,  SECTION  THROUGH  THE  UPPER  EYELID. 

a,  sweat  glands;  ai,  primary  tarsal  arch;  as,  secondary  tarsal  arch;  b,  conjuncti- 
val  epithelium;  c,  eyelashes;  co,  rugated  portion  of  the  conjunctiva;  d,  epidermis; 
e,  fine  hairs;  /,  process  of  the  levator  palpebra;  superioris  which  is  inserted  into  the 
skin;  g,  Meibomian  gland;  h,  internal  angle  of  the  margin  of  the  lid;  /,  levator  palpe- 
bra  superioris;  m,  duct  of  a  Meibomian  gland;  o,  orbicularis  palpebrarum  muscle; 
p,  superior  palpebral  muscle  of  Miiller;  r,  ciliary  muscle  of  Riolan;  s,  glands  of 
Moll;  t,  fibrous  tissue  of  the  tarsus;  v,  external  angle  of  the  margin  of  the  lid;  w, 
posterior  tarsal  glands;  2,  sebaceous  glands.  (After  Fuchs.) 


676  THE  EYE 

glands  open  into  the  hair  follicles  and  occasional  sudoriparous  glands 
pour  their  secretion  upon  the  epidermal  surface. 

At  the  margin  of  the  lid  its  cutaneous  portion  is  reflected  inward, 
and  at  its  inner  angle  becomes  directly  continuous  with  the  palpebral 
conjunctiva.  The  free  margin  of  the  lid  presents,  therefore,  an  outer 
angle,  an  inner  angle,  and  an  intermediate  surface. 

Two  or  three  rows  of  large  stiff  hairs,  the  eyelashes  or  cilia,  project 
from  the  outer  angle,  and  large  sebaceous  glands  open  into  their  follicles. 
Other  smaller  sebaceous  glands  open  directly  upon  the  free  surface. 
These  sebaceous  glands  are  sometimes  called  the  glands  of  Zeiss. 

The  intermediate  surface  of  the  margin  of  the  lid  retains  the  char- 
acter of  the  skin,  though  no  hairs  are  found  in  this  portion.  Peculiar 
sweat  glands,  the  glands  of  Moll,  occur  in  the  derma  of  this  part. 

At  the  inner  angle  of  the  lid  the  epidermis  abruptly  changes  its  char- 
acter to  that  of  the  conjunctiva,  the  derma  of  the  cutaneous  surface 
being  continuous  with  the  submucous  connective  tissue  of  this  membrane. 
At  the  inner  angle  also,  are  the  openings  of  the  peculiar  large  sebaceous 
glands,  the  tarsal  glands  (of  Meibom),  their  orifices  forming  a  con- 
tinuous punctate  row  of  pores  barely  visible  to  the  naked  eye. 

The  tarsal  (Meibomian)  glands  are  long  compound  saccular 
glands,,  about  thirty  in  the  upper,  and  about  twenty  in  the  lower  lid, 
whose  secreting  saccules  open  into  a  common,  axially  placed  duct  which 
extends  the  whole  length  of  the  gland.  Each  saccule  is  filled  with  cells 
in  various  stages  of  fatty  degeneration  and  is  exactly  similar  in  structure 
to  the  saccules  of  the  ordinary  sebaceous  glands.  The  glands  are  em- 
bedded in  the  connective  tissue  of  the  conjunctiva  and  are  so  large  as 
to  form  projecting  ridges  on  its  surface,  which  are  disposed  in  vertical 
lines  radiating  from  the  row  of  glandular  orifices  at  the  margin  of  the 
lid.  At  their  blind  extremities  the  glands  are  often  slightly  bent  or 
curved  upon  themselves,  and  this  portion  is  embedded  in  a  dense  mass 
of  fibrous  tissue  known  as  the  tarsus. 

The  tarsus  in  each  eyelid  forms  a  very  dense  plate-like  mass  of  areolar 
connective  tissue  which  is  so  dense  and  resistant  as  to  erroneously 
suggest  a  cartilaginous  structure.  It  is  inserted  between  the  conjunctiva 
and  the  orbicularis  muscle.  It  is  thickest  toward  the  free  margin  of 
the  lid,  but  becomes  progressively  thinner  in  the  opposite  direction,  until, 
as  a  mere  fibrous  membrane,  the  palpebral  fascia,  it  is  continued  to  the 
margin  of  the  orbit. 

The  conjunctival  portion  of  the  lids,  the  palpebral  conjunctiva, 
consists  of  a  peculiar  stratified  epithelium  and  a  thin  connective  tissue 


APPENDAGES  OF  THE  EYE  677 

corium.  Its  epithelium  comprises  four  or  five  layers  of  cells,  the  deeper 
of  which  are  small  and  spheroidal,  and  the  superficial  elongated  or  coni- 
cal, their  hlunt  ends  forming  the  free  surface  of  the  conjunctiva,  their 
pointed  extremities  buried  between  the  cells  of  the  deeper  layers.  The 
bases  of  these  elongated  -cells  become  somewhat  expanded  and  broader 
from  the  increased  tension  of  the  conjunctiva  when  the  lids  are  closed; 
they  retract  and  become  narrower  when  the  lids  are  separated  and  the 
conjunctiva  relaxed. 

The  cells  of  the  superficial  layer  are  often  so  distinctly  elongated 
as  to  possess  a  columnar  form.  They  may,  however,  be  spheroidal  or 
even  somewhat  flattened,  in  which  case  they  very  closely  resemble  the 
ordinary  type  of  stratified  squamous  epithelium.  The  epithelial  layer 
rests  almost  directly  upon  the  connective  tissue  corium,  the  basement 
membrane  being  imperfectly  developed. 

The  corium  of  the  conjunctiva  is  thin.  With  the  aid  of  a  thin  layer 
of  submucous  areolar  tissue  it  unites  the  epithelium  to  the  tarsus  and 
to  the  fibers  of  the  orbicular  is  muscle;  near  the  margin  of  the  lid  its 
submucous  tissue  incloses  the  Meibomian  glands.  Opposite  the  plane 
at  which  the  blind  ends  of  the  Meibomian  glands  are  embedded  in  the 
free  margin  of  the  tarsus,  the  conjunctival  surface  is  thrown  into  eight 
to  twelve  horizontal  folds,  beneath  which,  in  the  connective  tissue,  are 
a  few  minute  tubulo-alveolar  glands,  the  posterior  tarsal  glands  (glands 
of  Waldeyer;  glands  of  Henle).  Their  ducts  open  upon  the  free  surface 
of  the  conjunctiva  near  the  fornix  conjunctiva?. 

At  the  attached  base  of  the  lid  a  narrow  band  of  smooth  muscle  dx- 
tends  from  the  levator  palpebra?  and  inferior  oblique  muscles  into  the 
body  of  the  lid.  These  fibers  have  been  described  by  H.  Miiller  (1858) 
as  the  superior  and  inferior  palpebral  muscle  of  the  upper  and  lower 
lid,  respectively,  and  have  come  to  be  known  as  the  muscle  of  Miiller. 

The  fold  by  which  the  palpebral  conjunctiva  is  reflected  upon  the 
globe  of  the  eye  to  become  continuous  with  the  ocular  portion  of  the 
membrane  is  known  as  the  fornix  conjunctives.  The  extremely  loose 
attachment  of  the  conjunctiva  of  the  fornix  to  the  underlying  connective 
tissue  and  intra-orbital  fat  permits  the  great  freedom  of  motion  which 
is  characteristic  of  the  ocular  globe.  The  small  accessory  lacrimal  glands 
(glands  of  Krause)  open  into  the  margin  of  the  fornix  conjunctiva?. 
The  superior  fornix  contains  from  eight  to  twenty,  the  inferior  from 
two  to  five.  In  this  region,  also,  occasional  goblet  cells  occur  in  the 
superficial  layers  of  the  epithelium. 

The  ocular  conjunctiva  is  likewise  very  loosely  attached  to  the  sclera. 


678 


THE  EYE 


The  scleral  portion  of  the  conjunctiva  is  nearly  identical  in  structure 
with  the  palpebral  portion  already  described.  Near  the  margin  of  the 
cornea  the  superficial  cells  of  the  epithelium  become  at  first  spheroidal 
and  then,  as  the  cornea  is  approached,  they  are  progressively  flattened, 
so  that,  just  outside  of  the  corneal  margin,  the  conjunctival  epithelium 
conforms  to  the  stratified  squamous  type  which  forms  the  anterior  epi- 
thelium of  the  cornea. 

The  blood  supply  of  the  eyelids  is  derived  from  the  internal  palpe- 
bral artery  which  furnishes  a  branch  to  each  lid;  these  two  branches 

anastomose  at  the  external  angle 
with  the  lacrimal  branch  of  the 
ophthalmic,  through  the  external 
palpebral  artery.  These  trans- 
verse AETERIAL  VESSELS  (primary 
tar  sal  arches)  lie  near  the  free 
margin  of  the  lids  between  the 
tarsus  and  the  orbicularis  palpe- 
brarum  muscle.  Each  tarsal  arch 
sends  pre-tarsal  twigs  forward  to 
supply  the  muscle  and  integu- 
ment, and  post-tarsal  twigs  back- 
ward to  supply  the  tarsal  fascia, 
the  tarsal  glands  and  the  conjunc- 
tiva. At  the  basal  end  of  the  tar- 
sus, just  back  of  the  levator  pal- 
pebrae  muscle,  a  second  arch  (the 
(secondary  tarsal  arch)  may  be  present,  more  commonly  in  the  upper 
lid ;  this  second  arch  represents  a  larger  branch  of  the  palpebral  artery, 
and  it  anastomoses  freely  with  the  primary  arch.  The  VEINS  follow  an 
essentially  similar  course.  The  LYMPHATICS  likewise  include  a  pre-  and 
post-tarsal  set,  wrhich  unite  to  form  larger  tarsal  tributaries  which  drain 
along  the  facial  vein  toward  the  submaxillary  lymph  nodes. 

Tbe  nerve  supply  includes  sensory,  motor  and  sympathetic  fibers. 
The  main  trunks  lie  between  the  tarsus  and  the  orbicularis  palpebrarum 
muscle.  The  sympathetic  fibers  supply  the  blood-vessels,  the  smooth 
muscle  of  Miiller,  and  the  glands.  Motor  fibers  contributed  by  the  facial 
nerve,  supply  the  annular  sheet  of  striped  muscle;  the  oculomotor 
nerve  contributes  motor  fibers  to  the  levator  palpebra  muscle.  The 
sensory  fibers,  which  are  derived  from  the  trigeminal  nerve,  end  in  naked 
fibrils  among  the  cells  of  the  external  integument  and  the  internal  con- 


FIG.  568. — ARTERIAL  SUPPLY  OF  THE  EYE- 
LID. 

(After  Fox.) 


APPENDAGES  OF  THE  EYE  679 

junctiva,  and  in  the  subcutaneous  connective  tissue  and  the  tarsus. 
Numerous  sensory  fibrils  end  also  in  special  end-bulbs,  especially  along 
the  inner  margin  of  the  lids;  similar  endings  occur  in  the  palpebral  and 
bulbar  conjunctiva. 

THE  LACRIMAL  LAKE 

In  the  Q  -shaped  area  of  the  internal  canthus,  the  laciLs  lacrimalis, 
lies  a  roughened  irregular  reddish  mass  of  delicate  modified  skin,  the 
caruncle  (caruncula  lacrimalis).  It  is  embedded  in  fat  and  contains 
a  number  of  very  delicate  hairs,  large  sebaceous  glands  and  a  few  sweat 
glands.  Where  the  borders  of  the  lake  pass  into  the  palpebral  margins 
there  appears  a  slightly  raised  papilla  lacrimalis,  each  of  which  contains 
an  apical  opening,  the  puncta  lacrimalia,  leading  into  the  two  canaliculi 
lacriinales,  which  conduct  the  excess  of  lacrimal  secretion  or  tears  into 
the  nasolacnmal  duct.  To  the  outer  side  of  the  lacrimal  lake  there 
appears  a  vertical  crescentic  fold  of  delicate  skin,  the  plica  semilunaris, 
which  is  the  homologue  of  a  functional  third  eyelid  (nictitating  mem- 
brane) of  birds  and  reptiles. 


THE  LACRIMAL   GLAND 

The  lacrimal  glands  are  two  flattened,  lobulated,  glandular  masses 
situated  at  the  upper  and  outer  angle  of  the  orbit,  one  in  relation  with 
each  eye.  They  secrete  a  clear  watery  fluid,  the  tears.  These  glands 
are  somewhat  molded  to  conform  to  the  shape  of  the  orbit  and  the  globe 
of  the  eye,  between  which  they  are  inserted. 

Each  lacrimal  gland  is  a  secreting  gland  of  the  compound  tubular 
type  (Marziarski)  (Fig.  257,  page  258),  and  consists  of  eight  to  twelve 
small  lobules  which  open  into  the  fornix  conjunctivas  by  about  as  many 
minute  ducts.  The  lobules  are  aggregated  into  two  fairly  distinct 
lobes,  separated  by  a  denser  fascia,  the  superior  lobe  or  orbital  portion 
and  the  inferior  lobe  or  palpebral  portion,  and  are  united  by  thin  fibrous 
fascia3  which  contain  the  larger  ducts. 

Each  lobule  of  the  gland  contains  many  serous-secreting  acini  and 
numerous  small  intralobular  ducts.  The  secreting  acini  are  lined  by 
tall,  columnar  cells,  resting  upon  a  thin  basement  membrane,  which 
is  supplied  with  'basket  cells'  and  is  invested  with  a  delicate  fibrous 
tunica  propria.  The  appearance  of  the  secreting  epithelium  differs  some- 


680 


THE  EYE 


what  according  to  its  state  of  activity.  After  a  period  of  rest,  and 
in  the  ordinary  condition  of  relative  inactivity,  the  epithelium  becomes 
distended  with  secretion  and  is  either  clear  in  appearance  or  at  most 
is  only  very  finely  granular,  the  nuclei  are  crowded  to  the  base  of  the 
swollen  cells,  and  the  lumen  of  the  acinus  is  very  small.  After  a  period 
of  excessive  activity  the  secreting  cells  become  shrunken  and  more  dis- 


FIG.  569. — SECTION  THROUGH  A  LOBULE  OF  THE  LACRIMAL  GLAND  OF  MAN. 

a,  small  duct  branching  within  the  lobule;  b,  intercalary  ducts;  c,  connective 
tissue;/,  fat  cells.  A,  transection  of  an  interlobular  duct.  Hematoxylin  and  eosin. 
X  112.  (After  Kolliker.) 

tinctly  granular,  and  the  lumen  of  the  acinus  appears  much  dilated. 

The  secreting  acini  empty  into  narrow  intercalated  ducts  which  lie 
within  the  lobule,  have  a  considerable  lumen,  and  are  lined  by  tall 
columnar  cells  resting  upon  a  second  incomplete  layer  of  small,  some- 
what flattened  basket  cells. 

These  intralobular  ducts  unite  at  the  margin  of  the  lobule  to  form 
the  larger  interlobular  ducts,  which  are  contained  in  the  interlobular 
connective  tissue.  Here  the  duct  is  lined  by  low  columnar  or  even 
somewhat  flattened  cells,  at  first  disposed  in  a  single,  but  later  in  a 


APPENDAGES    OF   THE    EYE 


681 


double  layer.  As  the  duct  approaches  the  conjunctival  surface  the 
number  of  cell  layers  increases  until  their  lining  epithelium  finally 
comes  to  resemble 
the  stratified  epi- 
thelium of  the  con- 
junctiva with  which 
it  is  continuous. 

Minute  collec- 
tions of  diffuse 
lymphoid  tissue 
and  even  small 
lymph  nodules  are 
occasionally  found 
just  beneath  the 
epithelium  of  t  h  e 
conjunctiva  in  the 
neighborhood  of  the 
lacrimal  glands  of 
the  f  ornix ;  occa- 
sionally the  lym- 
phoid tissue  is 
quite  abundant. 

In  animals  pos- 
sessing a  membrana 
nictitans  ('third 
lid')  a  small,  mu- 
cus-secreting gland 
occurs  at  the  inner 
angle  of  the  orbit ; 
this  is  known  as  the 
gland  of  Harder. 
It  is  well  developed 
also  in  some  mam- 
mals, e.g.,  rabbit, 
but  in  man  and 
other  primates  it  is 
usually  absent,  though  in  an  extremely  vestigial  condition  it  may  occa- 
sionally be  found  within  the  basal  portion  of  the  plica  semilunaris. 


FIG.  570. — PORTIONS  OF  Two  ADJACENT  LOBULES  OF  THE 
LACRIMAL  GLAND  OF  THE  RABBIT,  SHOWING  Two  STAGES 
IN  SECRETORY  ACTIVITY  OF  THE  TUBULES.     Magnifica- 
tion X  100. 
In  the  upper  lobule  the  cells  are  filled  with  minute,  in 

the  lower  lobule  with  large,  secretion  spherules. 


43 


CHAPTER    XIX 
THE   EAR 

This  organ  may  be  subdivided  for  description  into  the  external, 
the  middle,  and  the  internal  ear.  The  first  two  portions  serve  for  the 
collection  and  transmission  of  sound  waves,  the  last  for  the  transforma- 
tion of  the  sound  waves  into  nerve  stimuli  which  are  then  transmitted 
through  the  path  of  the  acoustic  nerve  to  the  cerebrum. 


THE  EXTERNAL  EAR 

The  external  ear  includes  an  auricular  or  free  portion  and  an  ex- 
ternal acoustic  (auditory)  meatus. 

THE  AURICLE 

The  auricle,  or  pinna,  contains  a  thin  cartilaginous  plate  of  peculiar 
form  which  is  covered  on  both  sides  by  the  skin.  The  cartilage  is  of 
the  elastic  variety,  but  differs  from  the  similar  cartilages  of  other  parts 
in  the  abundance,  of  its  large  cartilage  cells;  in  occasional  areas  the 
elastic  reticulum  is  deficient.  This  reticulum  is  closely  connected  with 
the  fibrous  perichondrium,  beneath  which  it  forms  a  complete  layer. 
The  extrinsic  muscles  of  the  ear  are  inserted  into  the  perichondrium 
and  the  fibrous  tissue  by  which  it  is  surrounded. 

The  skin  of  the  external  ear  does  not  essentially  differ  from  that 
of  other  parts.  It  is  supplied  with  fine  hairs  and  with  many  large 
sebaceous  glands;  sweat  glands  also  occur  on  the  outer  surface.  The 
derma  is  united  to  the  underlying  cartilage  by  connective  tissue;  on 
the  concave  surface  this  union  is  very  firm  and  permits  but  little  motion. 
The  subcutaneous  tissue,  except  in  the  lobule,  contains  but  little  fat. 
The  lobule  does  not  contain  cartilage. 

682 


THE  EXTEKNAL  EAE 


683 


THE   EXTERNAL  ACOUSTIC   MEATUS 

The  external  ACOUSTIC  MEATUS  (or  auditory  canal)  is  divisible  into 
an  outer  cartilaginous  and  an  inner  bony  portion;  the  walls  of  the  two 


FIG.  571. — TRANSECTION  OF  THE  LOBULE  or  THE  EXTERNAL  EAR  OP  AN  INFANT. 

a,  cartilage;  b,  skin;  c,  adipose  connective  tissue.    Hematein  and  eosin.    Photo. 
X  20. 


portions,  except  for  this  difference,  are  quite  similar  in  structure.  The 
cartilage  is  continuous  with  that  of  the  auricle,  and  is  of  the  cellular 
elastic  variety.  The  skin  of  this  portion  contains  large  stiff  hairs  and 
both  sebaceous  and  ceruminous  glands.  The  former,  as  in  the  auricle, 


684 


THE  EAE 


open  either  upon  the  free  surface  of  the  skin  or  into  the  adjacent  portion 
of  the  hair  follicles. 

THE  CERUMINOUS  GLANDS 

The  ceruminous  glands  resemble  in  structure  the  sweat  glands  of 
other  portions.  They  are  coiled  tubular  glands  which  open  upon  the 
surface  of  the  skin  by  means  of  a  narrow  duct.  The  coils  of  their  se- 
creting portion  are  lined  by  columnar  cells  with  spheroidal,  basally 


FIG.  572. — FROM  THE  EXTERNAL  ACOUSTIC  MEATUS  OF  MAN. 

a,  sebaceous  gland;  b,  ceruminous  gland;  c,  cartilage.     Hematoxylin  and  eosin. 
X  15.     (After  Sobotta.) 


situated  nuclei  and  a  clear  cytoplasm  containing  many  small  brownish 
granules  of  pigment  and  a  few  fatty  particles.  The  cytoplasm  is  often 
diffusely  colored  by  the  brownish  pigment.  Between  the  lining  cells 
and  the  basement  membrane  appear  slender  fusiform  elements  re- 
sembling similarly  placed  elements  in  the  sweat  glands,  and  likewise 
interpreted  as  muscle  cells.  The  secretion  of  these  glands,  the  cerumen, 
in  addition  to  the  pigmented  and  fatty  secretion  of  the  glands,  contain? 


THE  MIDDLE  EAR  685 

sebum,  desquamated  epithelial  cells  and  occasional  fine  hairs,  together 
with  foreign  particles  of  a  very  varied  sort. 

In  the  bony  portion  of  the  meatus  the  corium  or  derma  is  firmly 
adherent  to  the  periosteum  of  the  bone,  and  all  the  layers  of  the  skin 
are  much  reduced  in  thickness.  The  scanty  hairs  are  very  fine,  and, 
with  the  glands,  are  continued  inward  to  the  tympanic  membrane  only 
in  the  superior  portion  of  the  wall  of  the  canal.  Papilla?  are  present 
as  far  as  the  margin  of  the  tympanic  membrane.  Upon  the  surface  of 
this  membrane,  which  closes  the  inner  end  of  the  external  acoustic 
meatus  and  separates  it  from  the  cavity  of  the  middle  ear,  the  skin  is 
reduced  to  an  extremely  thin  cutaneous  coat,  devoid  of  hairs,  glands, 
and  papilla?. 

THE   MIDDLE  EAR 

GENERAL  CONSIDERATIONS 

The  middle  ear  or  tympanum  ('ear-drum')  is  an  irregular  cavity, 
broad  above  and  behind,  narrow  below  and  in  front,  which  lies  just 
within  the  external  acoustic  meatus.  Its  outer  wall  is  largely  formed 
by  the  tympanic  or  drum  membrane,  its  inner  by  the  osseous  wall  of  the 
internal  ear. 

The  contour  of  the  tympanum  is  very  irregular,  its  cavity  being 
encroached  upon  by  numerous  bony  elevations  which  are  most  pro- 
nounced on  its  internal  wall.  Externally  the  tympanic  membrane  is 
attached  to  a  bony  and  fibrocartilaginous  ring,  the  annulus  tympanicus, 
which  projects  somewhat  into  the  tympanic  cavity.  In  front,  the  orifice 
of  the  auditory  (Eustachian)  tube  is  marked  by  a  slight  cartilaginous 
projection  near  the  floor  of  the  cavity. 

Above  and  behind,  the  tympanic  cavity  is  prolonged  into  a  deep 
recess,  the  epitympanic  cavity,  in  the  upper  part  of  whose  posterior 
wall  are  the  orifices  of  the  mastoid  cells.  The  upper  portion  of  the 
cavity  contains  the  rounded  heads  of  the  malleus  and  incus,  the  two 
largest  of  the  auditory  ossicles.  The  internal  wall  of  the  tympanum 
presents  anteriorly  a  bulging  prominence  which  is  known  as  the  promon- 
tory, and  which  indicates  the  position  of  the  first  or  broadest  turn  of 
the  spiral  canal  of  the  cochlea.  Beneath  this  prominence  is  a  recess 
leading  to  a  bony  'window/  the  fenestra  cochlece  (or  fenestra  rotunda), 
which,  in  life,  is  closed  by  a  delicate  membrane,  the  secondary  tympanic 
membrane.  Behind  the  promontory  and  at  a  slightly  higher  level  a 


686  THE  EAE 

deep  recess,  the  pelvis  ovalis,  leads  inward  to  the  fenestra  vestibuli  (or 
fenestra  ovalis),  which  is  closed  by  the  base  of  the  stapes;  the  body  of 
this  ossicle  is  contained  entirely  within  the  pelvic  recess,  and  near  its 
mouth  the  stapes  articulates  with  the  orbicular  extremity  of  the  long 
process  of  the  incus.  The  superior  portion  of  this  deep  recess  is  en- 
croached upon  by  the  projecting  wall  of  the  aqueductus  Fallopii  which 
transmits  the  facial  nerve.,  and  posteriorly,  near  the  point  where  it 
merges  with  the  general  tympanic  cavity,  a  low,  conical,  bony  projection 
known  as  the  pyramid  transmits  the  stapedius  muscle.  The  canal  of  the 
tensor  tympani  muscle  contained  within  a  still  more  prominent,  conical, 
bony  projection,  the  processus  cochleariformis,  is  found  near  the  antero- 
internal  angle  of  the  tympanic  cavity  just  above  and  parallel  to  the 
auditory  tube.  The  narrowest  portion  of  the  tympanum  is,  perhaps, 
almost  its  very  center,  and  is  included  between  the  promontory  on 
the  inner  and  the  tympanic  membrane  on  the  outer  side.  Extending 
from  this  narrowed  central  portion  upward,  backward,  and  inward,  are 
expanded  recesses  which  are  partially  occupied  by  the  three  auditory 
ossicles ;  the  remaining  portions  of  the  tympanum  are  filled  by  air  which 
gains  access  to  the  cavity  through  the  auditory  tube. 

THE  TYMPANIC   MUCOSA 

The  tympanic  mucosa  consists  of  a  thin  but  dense  tunica  propria 
which  is  firmly  attached  to  the  underlying  periosteum  and  softer  parts 
by  loose  connective  tissue,  and  is  clothed  with  a  layer  of  flattened  ento- 
dermal  epithelium,  which,  in  the  vicinity  of  the  origin  of  the  auditory 
tube,  is  of  low  columnar  form  and  is  provided  with  cilia,  but  in  most 
other  portions  of  the  tympanum  is  squamous  in  character  and  of  the 
tessellated  type,  closely  resembling  endothelium.  The  floor  of  the  tym- 
panum and  the  lower  portions  of  its  anterior,  internal,  and  posterior 
walls  also  possess  a  partial  clothing  of  low  ciliated  cells  (Kessel).  Occa- 
sional gland-like  folds  of  the  mucosa  occur  near  the  orifice  of  the  audi- 
tory tube,  though  the  true  glandular  character  of  these  folds  is  very 
questionable. 

THE   MASTOID   CELLS 

The  mastoid  cells  (cellules  mastoidece  sen  pneumaticce)  are  numer- 
ous small  spaces  situated  within  the  mastoid  process  of  the  temporal 
bone;  they  are  lined  by  a  continuation  of  the  tympanic  mucosa,  which 
is  everywhere  clothed  by  flattened  epithelium.  The  corium  is  closely 
attached  to  the  periosteum  of  the  bony  wall,  the  periosteum  also  serving 


THE  MIDDLE  EAR 


687 


as  a  vascular  layer  of  the  mucosa  in  the  mastoid  cells,  as  well  as  in 
the  general  tympanic  cavity. 


THE  TYMPANIC  MEMBRANE 

The  tympanic  membrane  is  a 
thin  delicate  partition  which  is 
formed  by  a  reflection  of,  the 
cutaneous  layer  of  the  external 
acoustic  meatus  on  the  one  hand, 
the  tympanic  mucosa  on  the 
other,  and  between  these  two 
membranes  a  layer  of  dense  fi- 
brous tissue  whose  tendinous 
bands  are  disposed  in  radial  and 
circular  directions.  The  margin 
of  the  tympanic  membrane  is  in- 
serted into  a  fibrocartilaginous 
ring  which  rests  upon  a  bony  ele- 
vation, the  annulus  tympanicus. 

The  slender  manubrium  or 
handle  of  the  malleus  projects 
from  the  superior  margin  of  the 
ring  and  is  inserted  between  the 
folds  of  the  tympanic  membrane, 
extending  downward  to  about  the 
center  of  the  membrane,  at  which 
point  is  the  deepest  part  of  its 
concavity,  its  umbo.  The  bony 
handle  of  the  malleus,  lying  be- 
tween the  cutaneous  and  mucous 
layers  of  the  tympanic  membrane, 
is  covered  by  a  thin  cartilaginous 
layer,  and  receives  the  insertions 
of  the  tendinous  fibers.  These 
fibers  are  divisible  into  an  outer 
radial  layer  which  extends  from 
the  fibrocartilaginous  ring  at  the 

periphery  inward  to  the  manubrium  mallei,  and  an  inner  circular  layrs 
whose  thickest  portions  are  found  close  to  the  manubrium  and  near  tne 


FIG.   573. — TRANSECTION   OF   THE   TYM- 
PANIC MEMBRANE  OF  A  CHILD. 

a,  a',  fibrocartilaginous  ring;  b,  b',  bone; 

c,  c',  skin  of  the  external  acoustic  meatus; 

d,  d',  tympanic  mucosa;  e,  cutaneous  layer 
of   the   tympanic   membrane;  /,    fibrous 
layer,  obliquely  cut  at/';  g,  layer  derived 
from  the  tympanic  mucosa;  h,  handle  of 
the  malleus;  i,  blood-vessels.     Hematoxy- 
lin  and  eosin.     X   11.     (After  Kolliker.) 


G88 


THE  EAE 


periphery  of  the  membrane;  between  these  points  the  circular  layer  of 
fibers  is  partially  or  entirely  deficient     Just  within  the  fibrocartilagi- 

nous  ring  at  the  periphery 
of  the  membrane  the  cir- 
cular layer  of  fibers 
abruptly  ends. 

The  cutaneous  layer 
of  the  tympanic  membrane 
forms  a  very  thin  coat,  "its 
epidermis  consisting  of  a 
germinal  layer  one  or  two 
cells  deep,  which  is  cov- 
ered by  several  flattened 
non-nucleated  cells  of  the 
horny  portion.  The  derma 
or  corium  is  very  thin, 
contains  no  papillae,  and 
is  intimately  adherent  to 
the  fibrous  layers  of  the 
membrane ;  it  contains 
neither  glands  nor  hairs. 
The  mucous  layer  of 
the  tympanic  membrane 
is  even  thinner  than  the 
cutaneous.  It  consists  of 
a  flattened  entodermal 
epithelium  which  rests  al- 
most directly  upon  the 
layer  of  circular  fibers. 
A  few  connective  tissue 
fibers  pass  irregularly 
from  the  mucous,  through 
the  fibrous,  to  the  cu- 
taneous layer,  thus  firm- 
ly uniting  the  several  lay- 
ers into  a  compact  mem- 
brane. 

In  the  upper  quadrant  of  the  tympanic  membrane,  above  the  at- 
tachment of  the  malleus,  the  fibrous  layers  are  wanting;  the  mucous 
and  cutaneous  layers  are  therefore  in  contact,  and  the  membrane  presents 


FIG.  574. — SECTION  THROUGH  THE  MARGIN  OF  THE 
TYMPANIC  MEMBRANE  OF  A  CHILD. 

a,  fibrocartilaginous  ring;  6,  bone;  c,  derma  of 
the  external  auditory  canal;  d,  tympanic  mucosa; 
e,  e',  epidermis;  /,  radial  fibers,  and  /',  circular 
fibers  of  the  tympanic  membrane;  g,  mucosa  of  the 
membrane;  h,  epithelium  of  the  tympanum;  i, 
blood-vessels.  X  55.  (After  Kolliker.) 


THE  MIDDLE  EAR  689 

a  flaccid  appearance  in  comparison  with  the  tense  condition  of  its  other 
parts.  This  portion  is  known  as  the  membrana  flaccida  or  Slirapnell's 
membrane. 

THE  AUDITORY   OSSICLES 

These  are  three  in  number,  the  malleus,  the  incus,  and  the  stapes ; 
they  form  a  continuous  bony  chain,  extending  from  the  insertion  of 
the  manubrium  mallei  in  the  tympanic  membrane  to  the  fenestra  vestib- 


FIG.  575. — THE  AUDITORY  OSSICLES. 

I,  ossicular  chain  of  the  left  ear;  1,  malleus;  2,  incus;  3,  stapes.  II,  ossicular 
chain  of  the  right  ear;  1,  malleus;  2,  processus  gracilis;  3,  manubrium;  4,  long  process 
of  the  incus;  5,  short  process  of  the  incus;  6,  stapes.  (After  Riidinger.) 

uli,  with  whose  margin  the  foot  of  the  stapes  articulates.  The  ossicles 
consist  of  compact  bony  tissue  containing  loosely  packed  Haversian  sys- 
tems; they  are  united  with  each  other  by  firm  fibrocartilaginous  ar- 
ticulations. With  the  exception  of  the  stapes,  none  of  the  ossicles  contain 
a  marrow  cavity. 

The  manubrium  of  the  malleus  is  firmly  fixed  in  the  tympanic  mem- 
brane, as  already  described,  the  head  of  the  bone  articulating  with 
the  head  of  the  incus  in  the  epitympanic  recess.  The  long  process  of 
the  incus,  circular  in  transection,  extends  downward  along  the  tympanic 
wall  in  a  course  nearly  parallel  to  that  of  tbe  manubrium  mallei,  being, 
in  a  portion  of  its  course,  contained  within  a  recess  in  the  osseous  wall 
of  the  tympanum.  Finally,  at  the  level  of  the  stapes  it  makes  a  sharp 
bend,  almost  at  right  angles  with  its  former  course,  to  articulate,  by 
means  of  a  rounded  end  or  orbicular  process,  with  the  head  of  the 


690 


THE  EAE 


This  latter  bone  is -deeply  placed  within  the  recess  of  the  pelvis 
ovalis,  and  continues  the  bony  chain  to  the  fenestra  vestibuli,  where 
the  foot  plate  of  the  stapes  is  in  relation,  by  its  inner  surface,  with  the 
vestibular  perilymphatic  space  of  the  internal  ear. 

The  course  of  the  chain  of  ossicles  is  such  that  they  form  a  lever; 
the  long  process  of  the  incus  being  shorter  than  the  manubrium  mallei, 
the  vibrations  of  the  tympanic  membrane  in  response  to  sound  waves 
are  transmitted  to  the  internal  ear  diminished  in  amplitude  but  ex- 
aggerated in  intensity. 
The  combined  activity  of 
the  tympanic  membrane 
and  the  auditory  ossicles 
is  said  to  reduce  the  am- 
plitude as  much  as  sev- 
enty-six times,  and  to 
increase  the  force  of  the 
vibrations  thirty  times. 

Two  muscles  and  sev- 
eral ligaments  are  con- 
nected with  the  ossicles. 
The  tensor  tympani 
i,  the  body  of  the  incus;  I,  ligamentous  fold  of  the  muscle  is  mostly  con- 
mucosa;  l.a.m.,  anterior  ligament  of  the  malleus; 
l.e.m.,  external  ligament  of  the  malleus;  Li.,  pos- 
terior ligament  of  the  incus;  M,  mastoid  cell;  m, 
head  of  the  malleus;  m.m.,  mucous  membrane;  n, 
chorda  tympani  nerve;  pr.  o.,  orbicular  process  of  the 
incus  articulating  with  the  stapes  in  the  depth  of 
the  cavity;  R,  beneath  this  space  is  the  flaccid  por- 
tion of  the  tympanic  membrane;  s.l.m.,  cut  end  of 
the  superior  ligament  of  the  malleus;  sp,  spina  tym- 
panica  anterior;  st,  st',  tendon  of  the  stapedius 
muscle;  tt,  tendon  of  the  tensor  tympani  muscle. 
X  4.  (After  Schafer.) 


&CC.77Z 


FIG.  576. — THE  CAVITY  OF  THE  TYMPANUM,  VIEWED 
FROM  ABOVE. 


tained  within  a  canal 
which  is  parallel  to  and 
lies  just  above  the  audi- 
tory tube,  and  from  its 
bony  wall  the  muscular 
fibers  arise.  The  wall  of 
the  canal  forms  a  conical 
projection  known  as  the 
processus  cochleariformis, 


which  projects  well  into 

the  cavity  of  the  tympanum,  being  directed  toward  the  neck  of  the  mal- 
leus. Leaving  its  canal  at  the  apex  of  this  conical  process  the  tendon 
of  the  muscle  bends  sharply  over  the  margin  of  the  processus  cochleari- 
formis and  passes  directly  to  its  insertion  into  the  neck  and  the  adjoin- 
ing part  of  the  manubrium  of  the  malleus.  Hence  the  naked  tendon  of 
the  muscle  lies  within  the  tympanic  cavity. 

The  stapedius  muscle   is  similarly  contained  within  the  cavity  of 
the  pyramid,  from  whose  bony  wall  its  fibers  take  origin.     Passing  for- 


THE  MIDDLE  EAE  691 

ward,  the  muscle  makes  its  exit  at  the  apex  of  the  pyramid,  and  is  di- 
rectly inserted  into  the  neck  of  the  stapes  close  to  the  articulation 
of  the  orbicular  process  of  the  incus. 

The  ligaments  of  the  malleus  are  the  anterior,  the  external,  and 
the  superior.  The  anterior  ligament  firmly  attaches  the  head  of  the 
malleus  to  the  margin  of  the  Glaserian  fissure  in  the  anterior  wall  of 
the  tympanum.  The  processus  gracilis  of  the  malleus  is  inclosed  by 
the  fibers  of  this  ligament.  It  is  also  in  close  relation  with  the  chorda 
tympani  nerve,  which,  being  clothed  by  the  tympanic  mucosa,  trav- 
erses this  portion  of  the  tympanic  cavity  and  enters  the  iter  chordae 
anterius. 

The  external  ligament  connects  the  neck  of  the  malleus  with  the 
upper  portion  of  the  external  wall  of  the  tympanum.  It  is  somewhat 
fan-shaped.  The  space  lying  between  the  external  ligament  of  the 
malleus  and  the  membrana  flaccida  is  known  as  Prussak's  space.  The 
superior  ligament  is  a  looser  fibrous  band  which  passes  from  the  head 
of  the  malleus  to  the  superior  wall  of  the  tympanum. 

The  ligament  of  the  incus  is  decidedly  fan-shaped,  its  straight,  coarse, 
fibrous  bands  radiating  from  the  short  process  of  the  ossicle  to  the  ad- 
jacent portion  of  the  posterior  wall  of  the  tympanum. 

The  articulation  of  the  malleus  with  the  incus,  as  also  that  of  the 
latter  bone  with  the  stapes,  is  supplied  with  a  delicate  capsular  liga- 
ment. 

The  annular  ligament  of  the  stapes  connects  the  margin  of  the 
foot  plate  of  this  bone  with  the  adjacent  portions  of  the  cartilaginous 
and  bony  wall  of  the  vestibule  at  the  margin  of  the  fenestra  vestibuli. 
The  articulation  which  is  thus  inclosed  is  directly  formed  by  an  an- 
nular plate  of  cartilage  investing  the  margin  of  the  oval  foot  of  the 
stapes,  and  a  similar  annular  plate  of  hyaline  cartilage  which  lines  the 
borders  of  the  foramen  vestibuli.  The  fibers  of  the  annular  ligament 
are  continuous  with  those  of  the  perichondrium  and  adjacent  periosteum. 

THE  AUDITORY   (EUSTACIIIAN)    TUBE 

The  auditory  or  Eustachian  tube  connects  the  cavity  of  the  tym- 
panum with  that  of  the  nasopharynx.  Its  first  portion,  including 
about  one-third  of  its  entire  length,  is  surrounded  by  a  bony  wall;  be- 
yond this  it  is  supplied  with  a  cartilaginous  plate;  its  pharynqjeal  ostium 
is  entirely  membranous. 

The  mucosa  consists  of  an  entodermal  epithelium,  which   is  of  the 


692  THE  EAE 

columnar  ciliated  variety,  continuous  with,  and  similar  to  the  respiratory 
epithelium  of  the  nasopharynx,  together  with  a  fibrous  membrana 
propria  which  is  loosely  connected  with  the  surrounding  bony,  car- 
tilaginous, and  muscular  walls.  The  lower  portions  of  the  tube  are 
richly  supplied  with  mucus-secreting,  tubulo-acinar  glands,  and  toward 


FIG.  577. — TRANSECTION  OF  THE  EUSTACHIAN  TUBE;  DIAGRAMMATIC. 

1,  cartilaginous  plate;  2,  lateral  or  hooked  end  of  the  cartilage;  8,  ' dilator  tubss * 
(tensor  palati);  4,  levator  palati;  5,  fibrocartilage  at  the  base  of  the  skull;  6  and  7, 
mucous  glands;  8,  adipose  tissue;  9,  11,  lumen  of  the  tube;  10,  12,  connective  tissue. 
Low  magnification.  (After  Riidinger.) 

its  pharyngeal  end  the  mucosa  is  much  infiltrated  with  lymphoid  tissue, 
thus  forming  the  tubal  tonsil  of  Gerlach. 

The  cartilage  of  the  auditory  tube  is  firmly  adherent  to  the  bony  wall. 
At  the  point  of  attachment  it  has  a  hyaline  structure,  the  fibers  of 
the  perichondrium  penetrating  only  the  surface  of  the  cartilaginous 
plate.  Lower  down  the  cartilage  becomes  infiltrated  with  fibers  and 
conforms  to  the  typical  elastic  variety.  Like  the  cartilage  of  the  auricle 
it  is  rich  in  cellular  elements.  Its  transection  presents  a  peculiar  hook- 
like  form,  by  means  of  which  the  posterior  surface,  the  superior  margin, 
and  the  upper  portion  of  the  anterior  surface  are  invested  by  cartilage, 


THE  INTERNAL  EAR  693 

while  the  remaining  portions  of  the  anterior  surface  and  the  whole 
of  the  inferior  margin  are  entirely  membranous.  Closely  associated 
with  the  auditory  tube  are  the  tensor  and,  levator  palati  muscles,  lying 
laterally  and  ventrally  to  the  tube.  These  muscles  serve  also  as  dilators 
for  the  tube. 

VASCULAR  SUPPLY 

The  Blood-vessels. — The  mucosa  of  the  middle  ear  is  richly  sup- 
plied with  blood-vessels,  the  larger  of  which  lie  in  the  deeper  part  of  the 
membrane  and  supply  capillary  vessels  to  the  tunica  propria.  The  blood- 
vessels of  the  auditory  tube  are  especially  numerous. 

In  the  tympanic  membrane  the  arteries  and  veins  form  an  annular 
plexus  at  the  margin;  and  a  group  of  similar  vessels  surrounds  the 
manubrium  mallei,  lying  in  the  deeper  layers  of  the  cutaneous  portion 
of  the  membrane. 

The  mucosa  of  the  tympanum  is  peculiar  in  the  relative  deficiency 
of  capillary  vessels  (Prussak,  1869) ;  the  veins  are  numerous.  The 
veins  of  the  auditory  tube  empty  into  the  internal  jugular;  they  also 
communicate  with  the  cavernous  sinus  by  a  trunk  of  considerable  size 
(Bench,  1895). 

The  lymphatics  of  the  middle  ear  form  plexuses  in  the  connective 
tissue  of  the  mucosa  and  in  a  general  way  follow  the  course  of  the 
smaller  veins.  They  lead  in  part  to  the  lymphatic  nodes  behind  the  ear, 
and  in  part  to  the  parotid  group  (Kolliker).  They  also  communicate 
with  the  perilymphatic  spaces  of  the  internal  ear. 


THE   INTERNAL  EAR 

GENERAL  CONSIDERATIONS 

The  internal  ear  includes  a  series  of  membranous  structures  together 
with  the  terminal  fibers  of  the  acoustic  nerve ;  these  are  contained  within 
a  series  of  connected  cavities  hollowed  out  of  the  petrous  portion  of 
the  temporal  bone,  and  in  relation  with  the  mesial  wall  of  the  tympanum. 
The  central  portion  of  this  bony  cavity,  an  ovoid  space,  is  known  as 
the  vestibule;  its  outer  wall  presents  the  orifice  of  the  fenestra  vestibuli 
which  leads  to  the  tympanum,  but  during  life  is  closed  by  the  base  of 
the  stapes.  Opening  from  the  vestibule,  at  one  end,  are  the  bony  cavi- 
ties occupied  by  the  three  semicircular  canals  which,  in  a  general  way, 


694  THE  EAE 

project  from  the  posterodorsal  aspect  of  the  vestibule;  at  the  other  end 
the  bony  cochlea  containing  its  series  of  spiral  canals  projects  anteriorly 
from  the  vestibule.  Collectively  these  spaces,  with  several  diverticula, 
form  the  bony  labyrinth,  and  within  them  in  life  are  contained  a  num- 
ber of  membranous  sacs  whose  general  form  corresponds  more  or  less 


FIG.  578. — THE  BONY  LABYRINTH. 

1,  round  window;  2,  osseous  lamina  spiralis;  3,  osseous  cochlear  canal;  4,  floor  of 
internal  acoustic  meatus;  5,  vestibule;  6,  7,  8,  9,  semicircular  canals.  The  figures 
are  placed  at  that  portion  of  the  margin  which  is  nearest  the  structure  indicated. 
(After  Rudinger.) 

closely  to  that  of  the  bony  cavity;  these  sacs  collectively  form  the  mem- 
branous labyrinth. 

The  vestibule  contains  two  of  these  membranous  sacs,  the  sacculus 
and  the  utriculus,  which  are  connected  by  means  of  the  slender  ulriculo- 
saccular  canal,  from  which  a  much  prolonged  diverticulum  enters  the 
aqueductus  vestibuli  to  penetrate  to  the  posterior  surface  of  the  petrous 
bone  where  it  comes  into  relation  with  the  cerebral  meninges;  this  di- 
verticulum is  known  as  the  ductus  endolymphaticus.  Its  dilated  terminal 
portion  constitutes  the  endolymphatic  sac,  which  lies  upon  the  dura  and 
probably  opens  into  the  subdural  space.  The  utricle  and  saccule,  as  also 
all  other  portions  of  the  membranous  labyrinth,  contain  a  watery  fluid, 


THE  INTEKNAL  EAE 


695 


the  endolymph;  they  do  not  entirely  fill  the  bony  cavity  of  the  labyrinth 
in  which  they  lie,  the  intervening  space  being  occupied  by  a  retiform 
connective  tissue  with  broad  interstices  which  are  permeated  by  an 
aqueous  fluid,  the  perilymph. 


THE    SACCULE 

The  saccule  is  a  rounded  membranous  cavity  which  is  connected, 
on  the  one  hand,  by  means  of  the  slender  canalis  reuniens,  with  the 
cochlear  duct  or  scala  media,  and  on  the  other  hand  with  the  ductus 
I'lidolymphaticus  and  utricle,  as  already  stated.  Its  wall  consists  of  an 


FIG.  579. — DIAGRAM  OF  THE  MEMBRANOUS  LABYRINTH  IN  LATERAL  VIEW. 

A,  ampullae;  U,  utricle;  S,  saccule;  SM,  scala  media  or  cochlear  duct;  CR,  canalis 
reuniens;  C,  crus,  or  common  canal;  SE,  saccus  endolymphaticus;  DE,  ductus  endo- 
lymphaticus;  dss,  dsp,  dsl,  superior,  posterior  and  lateral  (external)  semicircular 
ducts.  The  utricle  and  saccule  are  connected  by  the  utriculosaccular  duct.  The 
cochlear  duct  terminates  in  the  ceca  vestibulare  and  cupulare.  (After  Gray.) 


ectodermal  epithelium,  a  membrana  propria  and  a  fibrous  coat.  The  epi- 
thelium consists  of  flattened  squamous  cells;  it  completely  lines  the 
cavity.  The  epithelial  surface  is  somewhat  irregular  from  the  papillary 
elevations  of  the  fibrous  coat.  On  the  antero-inferior  surface  of  the  sac- 
cule the  epithelium  is  peculiarly  altered  so  as  to  form  a  layer  of  col- 
umnar cells,  many  of  which  are  provided  with  stiff  cilia.  This  neuro- 
epithelium  is  distributed  over  an  oval  area  (3  mm.  by  2  mm.  in  extent) 
beneath  which  the  fibrous  coat  is  much  thickened  by  the  entrance  of 
many  fibers  derived  from  the  vestibular  portion  of  the  acoustic  nerve, 


FIG.  580. — DIAGRAM  OF  THE  RIGHT  MEMBRANOUS  LABYRINTH. 

1,  utricle;  2,  superior  semicircular  canal;  8,  posterior  semicircular  canal;  4,  ex- 
ternal semicircular  canal;  5,  saccule;  6,  endolymphatic  duct;  7  and  7',  canals  con- 
necting utricle  and  saccule  respectively  with  the  endolymphatic  duct;  8,  endo- 
lymphatic sac;  9,  cochlear  duct;  9',  its  vestibular  cul-de-sac  (cecum  vestibulare) ; 
9",  its  terminal  cul-de-sac  (cecum  cupulare);  10,  canalis  reunions.  (After  Testut.) 


FIG.  581. — THE  ISOLATED  MEMBRANOUS  LABYRINTH. 

1,  utricle;  2,  saccule  (opened);  3,  location  of  the  macula  acustica  sacculi;  4,  am- 
pulla of  a  semicircular  canal;  5,  canalis  communis.  Low  magnification.  (After 
Rudinger.) 


THE  INTERNAL  EAB 


697 


This  elevation  with  its  neuro-epithelial  covering  is  known  as  the  macula 
acustica  sacculi. 

The  neuro-epithelium  contains  two  varieties  of  cells,  the  sustentacu- 
lar  and  the  hair  cells.  The  former,  fiber  cells  of  Eetzius,  form  a  layer, 
two  or  three  cells  deep,  which  rests  upon  the  basement  membrane, 
and  whose  broad  basal  portion  contains  a  spheroidal  nucleus.  Beyond 
the  nucleated  portion  the  cytoplasm  of  the  sustentacular  cell  is  con- 


FIG.  582. — TRANSECTION  OF  THE  MARGIN  OF  THE  MACULA  ACUSTICA  SACCULI  OF  A 
GUINEA-PIG. 

a,  otolithic  membrane;  b,  hairs;  c,  cuticular  membrane;  d,  hair  cells;  e,  susten- 
tacular cells;  /,  epithelium  of  the  saccule;  g,  tunica  propria;  h,  nerve  fibers;  i,  bone. 
Hematoxylin  and  eosin.  X  325.  (After  Kolliker.) 

tinued  inward  between  the  bodies  of  the  hair  cells  to  the  surface  of 
the  epithelial  layer,  this  portion  of  the  cell  being  relatively  slender. 

The  hair  cells  occupy  the  superficial  part  of  the  epithelial  layer 
by  their  broad  nucleated  portions,  which  carry  upon  their  free  extremity 
a  single  tuft  of  long  stiff  cilia,  having  the  appearance  of  a  delicate  hair- 
like  process  which  projects  into  the  endolymphatic  cavity.  That  por- 
tion of  the  endolymph  which  immediately  overlies  the  macula,  and 
into  which  the  hair-like  processes  project,  though  not  essentially  dif- 
ferent in  microscopic  appearance  in  fresh  tissues,  appears  to  possess  a 
somewhat  gelatinous  consistence,  and  in  it  are  suspended  various  forms 
of  minute  crystals  of  calcium  carbonate  which  are  known  as  otoconia 
or  'otoliths.'  The  free  surface  of  the  neuro-epithelium  is  also  provided 
44 


698 


THE  EAK 


with  a  reticulated  cuticular  membrane  which  presumably  is  formec  by 
the  amalgamation  of  the  free  ends  of  the  sustentacular  cells.  Through 
the  openings  in  this  reticular  membrane  the  ciliary  tufts  of  the  hair 
cells  project. 

The  central  ends  of  the  hair  cells,  beneath  the  nucleated  enlarge- 
ment which  is  found  near  the  middle  of  the  epithelial  layer,  are  pro- 
longed outward  between  the  nucleated  portions  of  the  sustentacular  cells 
and  frequently  terminate  in  small  knobbed  extremities.  This  portion 
of  the  cells  is  in  intimate  relation  with  the  terminal  fibrils  of  the  vestibu- 
lar  portion  of  the  acoustic  nerve,  which,  coming  from  a  nerve  plexus  in 

the  fibrous  wall  of  the  saccule, 
forms  an  intra-epithclial  plexus 
of  delicate  varicose  fibrils.  Fre- 
quently the  epithelial  coat  con- 
tains coarse  granules  of  a  brown- 
ish pigment  which,  at  times,  also 
produces  a  diffuse  coloration  of 
the  cells. 

The  lining  epithelium  of  the 
saccule  rests  upon  a  thin  homo- 
geneous basement  membrane  and 
is  further  supported  by  a  delicate 
fibrous  coat  or  tunica  propria. 
The  connective  tissue  of  this  coat  forms  interlacing  bundles  the  most 
of  which  are  distributed  in  a  circular  manner  about  the  wall  of  the 
ovoid  sacculus.  At  the  macula  this  coat  is  much  thickened  by  the  en- 
trance of  the  fibers  from  the  vestibular  nerve.  It  also  contains  the 
minute  blood-vessels  which  supply  the  organ. 

As  is  the  case  with  the  other  divisions  of  the  membranous  labyrinth, 
the  fibrous  wall  of  the  saccule  is  in  contact  on  one  aspect  of  its  surface 
with  the  periosteum  which  lines  the  osseous  labyrinth;  elsewhere  it  is 
separated  from  the  periosteum  by  the  perilymphatic  cavity. 


FIG.    583. — NERVE    ENDINGS    IN    THE 
MACULA  ACUSTICA  OP  A  GUINEA-PIG. 

a,  epithelium;  b,  tunica  propria;  c,  three 
terminal  nerve  fibers.  Golgi  stain.  X 
about  200.  (After  Retzius.) 


THE   UTRICLE 

The  utricle  is  somewhat  larger  than  the  saccule.  It  lies  behind 
and  somewhat  above  the  saccule,  is  of  a  very  irregular  oblong  form, 
and  receives  the  insertions  of  the  semicircular  canals.  Its  anterior 
portion  is  provided  with  a  macula  and  the  structure  of  its  wall 
differs  in  no  wise  from  that  of  the  saccule;  both  of  these  mem- 


THE  INTERNAL  EAE  699 

brauous  sacs  arc  contained  within  the  irregular  cavity  of  the  vestibule. 
The  structure  of  the  utriculus,  therefore,  requires  no  further  description. 

THE  SEMICIRCULAR  CANALS 

s 

The  semicircular  canals  or  ducts  are  three  in  number,  the  posterior, 
superior,  and  lateral.  The  last  is  also  horizontal  in  its  position;  the 
first  two  are  vertical,  but  are  so  placed  as  to  form  a  right  angle  with 
one  another.  The  posterior  lies  in  the  long  axis  of  the  petrous  bone 
and  its  plane  is  therefore  more  nearly  sagittal,  while  that  of  the  superior 
canal  is  more  nearly  coronal.  Each  canal  forms  something  more  than 
half  a  circle,  its  two  ends  opening  separately  into  the  cavity  of  the  vesti- 
bule, with  the  exception  of  the  posterior  and  superior  canals  whose  in- 
ternal ends  open  by  a  common  orifice,  the  ca/ta/ts  comments.  The  un- 
joined orifices  of  the  posterior  and  superior  canals,  as  also  the  outer 
extremity  of  the  lateral  canal,  present  a  marked  dilatation  at  their 
termination  in  the  vestibule.  These  dilatations  are  known  as  the  am- 
puttce.  They  lodge  the  neuro-epithelial  patches,  the  cristffi  acusticae. 
The  osseous  and  membranous  canals  are  of  similar  shape;  the 
latter  is,  of  course,  contained  within  the  former. 

The  membranous  semicircular  canals  open  into  the  utricle.  They 
do  not  entirely  fill  their  bony  canal,  but,  like  the  utricle  and  saccule, 
lie  in  contact  with  the  periosteum  at  one  surface  only,  this  surface  being 
that  of  the  outer  wall  or  periphery  of  the  semicircle,  while  in  the  re- 
maining portion  of  the  circumference  of  the  cylindrical  bony  duct,  the 
membranous  canal  is  loosely  united  to  the  periosteum  of  the  osseous 
wall  by  a  retiform  connective  tissue  whose  loose  meshes  are  filled  with 
perilymph  and  lined  with  mesenchymal  epithelium. 

The  wall  of  the  membranous  canal  is  similar  in  structure  to  that 
of  the  saccule  and  utricle  and  consists  of  an  ectodermal  epithelium,  a 
membrana  propria,  and  a.  fibrous  tunic.  Each  of  the  three  ampullse 
presents  a  marked  differentiation  of  the  epithelial  lining,  which  is  there 
raised  in  the  form  of  a  prominent  crescentic  fold,  inappropriately  termed 
by  the  older  anatomists  the  cmto  acustica,  from  its  supposed  connection 
with  the  auditory  function.  Like  the  macula?  of  the  saccule  and  utricle, 
the  cristaa  are  supplied  by  the  vestibular  nerve  and  are  concerned  with 
the  function  of  equilibration. 

The  utricle  and  saccule  represent  the  original  anlage  of  the  ear — 
the  otocyst — from  which  thfe-  canals  and  cochlea  arise  as  evagiuations; 
they  correspond  most  closely  also  to  the  'ear'  of  certain  invertebrates, 


700 


THE  EAR 


e.g.,  Crustacea,  which  is  simply  an  equilibrating  organ.  They  are  be- 
lieved to  function  as  static  organs  of  equilibration,  giving  information 
as  to  position  at  rest  or  during  progressive  movements ;  the  semicircular 
canals  on  the  other  hand  are  commonly  conceived  of  as  dynamic  or- 
gans of  equilibration  and  are  thought  to  furnish  information  regarding 
the  direction  and  extent  of  rotatory  movements. 


FIG.  584. — TRANSECTION  OF  A  HUMAN  SEMICIRCULAR  CANAL. 

1,  bone;  2,  retiform  connective  tissue  membranes;  3,  at  this  point  a  band  of  con- 
nective tissue  joins  the  periosteum;  4,  membranous  semicircular  canal;  5,  liga- 
mentous  attachment  of  the  canal;  6,  at  this  point  the  membranous  and  osseous 
canals  are  in  contact.  Moderately  magnified.  (After  Rudinger.) 


The  cristffi  are  clothed  with  tall  columnar  cells  which,  though  some- 
what taller,  are  otherwise  similar  in  structure  to  those  of  the  maculse, 
and  are  similarly  divisible  into  sustentacular  cells  and  hair  cells.  They 
are  also  covered  by  a  gelatinous  cuticular  formation,  containing  otoliths, 
which  is  here  known  as  the  cupola.  The  vibratory  stimulus  is  trans- 
mitted from  the  endolymph  to  the  hair  cells  through  the  medium  of 
the  otolithic  membranes. 


THE  INTERNAL  EAR 


701 


THE   COCHLEA 

The  cochlea,  like  the  vestibular  portion  of  the  internal  ear,  consists 
of  a  bony  case  which  incloses  a  membranous  organ. 

Structure. — The  bony  cochlea  possesses  a  peculiar  flat  pyramidal 
shape.  The  base  of  the  pyramid  is  in  contact  with  the  anterior  aspect 
of  the  vestibule;  its  apex  or  cupola  is  directed  forward,  outward,  and 
slightly  downward.  The  pyramid  is  hollow  and  contains  in  i'ts  axis  a 
conical  bony  support,  the  modiolus,  which  tapers  from  a  broad  base  to 
a  pointed  apex  beneath  the  broader, 
blunt,  and  rounded  cupola  of  the 
outer  bony  wall.  The  modiolus  con- 
tains a  broad  canal  which  receives 
the  cochlear  division  of  the  acoustic 
nerve  as"  it  enters  from  the  internal 
meat  us. 

The  outer  surface  of  the  modio- 
lus supports  a  bony  shelf,  the  lam- 
inn  vjnralis  ossea,  which  winds  in  a 
spiral  manner  from  its  base  to  its 
apex,  and  ends  in  a  hook-like  proc- 
ess, the  Tiamulus.  This  shelf  only 
partially  spans  the  interval  between 
the  modiolus  and  the  outer  wall  of 
the  cochlea.  In  life  the  remaining 
interval  is  completed  by  a  firm  fi- 
brous membrane,  the  basilar  membrane  (lamina  spiralis  membranacea) . 
Thus  the  cylindrical  canal  of  the  cochlea,  which  is  wound  spirally  around 
the  modiolus  making  two  and  one-half  turns  from  the  base  to  the  apex,  is 
subdivided  into  two  parallel  longitudinal  divisions,  which  are  respectively 
known  as  the  scala  vestibuli  and  the  scala  tympani.  They  are  so  dis- 
posed that  in  a  given  turn  of  the  canal  the  former  is  always  nearer  the 
apex,  the  latter  nearer  the  base  of  the  cochlea.  According  to  Wieder- 
sheim  (1893)  the  human  cochlea  has  nearly  three  turns,  the  pig  four, 
the  cat  three,  the  rabbit  two  and  one-half,  the  ox  three  and  one-half, 
and  cetacea  one  and  one-half  turns. 

The  osseous  lamina  spiralis  presents  a  grooved  margin  or  sulcus, 
from  the  basal  or  tympanic  lip  of  which  the  lamina  basilaris  is  con- 
tinued to  the  opposing  surface  of  the  bony  wall.  The  lamina  spiralis 
ossea  is  hollowed  out  in  a  diploic  manner  for  the  transmission  of  the 


FIG.   585. — AXIAL  SECTION  THROUGH 
THE  COCHLEA  OF  A  FETAL  CALF. 

a,  internal  acoustic  meatus  in  which 
is  the  cut  end  of  the  cochlear  nerve  as  it 
enters  the  modiolus.  X  6.  ^  After  Kol- 
liker.) 


702 


THE  EAE 


branches  of  the  cochlear  nerve,  which  are  continuously  given  off  all  the 
way  from  the  base  to  the  apex  of  the  osseous  spiral  lamina,  and  which 
pass  outward  through  the  foramina  nervosa  upon  the  basilar  membrane 


FIG.  586. — AXIAL  SECTION  THROUGH  A  TURK  OF  THE  COCHLEA  OF  A  GUIXEA-PIG. 

a,  bone  of  the  outer  wall  of  the  cochlea;  b,  membrane  of  Reissner;  d,  membrana 
tectoria;  DC,  cochlear  duct  or  scala  media;  /,  stria  vascularis;  g,  organ  of  Corti;  h, 
spiral  ligament;  i,  cells  of  Claudius;  A;,  scala  tympani;  I,  scala  vestibuli;  m,  vestibular 
lip  of  the  limbus  spiralis;  n,  internal  spiral  sulcus;  o,  nerve  fibers  of  the  cochlear 
nerve,  contained  within  one  of  the  radiating  canals  within  the  osseous  spinal  lamina; 
p,  nerve  cells  of  the  spiral  ganglion;  q,  blood-vessel;  r,  external  spiral  sulcus,  upon 
which  open  Shambaugh's  glands;  s,  prominentia  spiralis,  containing  the  vas  prom- 
inens.  X  90.  (After  Bohm  and  von  Davidoff.) 

to  be  distributed  to  the  epithelium  of  the  spiral  organ  (of  Corti).  This 
organ  is  a  peculiar  spiral  group  of  neuro-epithelial  cells  which  extends 
the  whole  length  of  the  basilar  membrane  from  the  base  to  the  cupola 
of  the  cochlea. 


THE  INTERNAL  EAE  703 

The  margin  of  the  osseous  spiral  lamina  is  much  thickened  by 
the  fibrous  and  epithelial  tissues  by  which  it  is  invested,  so  that  a  mem- 
branous sulcus  of  considerable  depth  is  formed  between  the  two  lips 
(vestibular  and  tympanic  lips)  of  the  bony  sulcus  •spiralis  internus. 
This  is  further  thickened  by  a  marked  elevation  of  fibrous  tissue  cov- 
ered by  columnar  cells,  from  the  outer  margin  of  which  a  delicate  mem- 
brane, the  membrana  tectoria,  extends  outward  and  overhangs  the  epi- 
thelium of  Corti's  organ.  From  the  inner  margin  of  the  elevation  of 
fibrous  tissue,  the  limbus  spiralis,  which  is  supported  by  the  vestibular 
lip  of  the  bony  lamina,  a  delicate  membrane,  the  vestibular  membrane 
(of  Eeissner},  passes  obliquely  outward  to  the  bony  wall  of  the  cochlea, 
and  in  transections  appears  to  cut  off  a  corner  of  the  scala  vestibuli, 
thus  marking  off  a  triangular  space  whose  base  is  formed  by  the  outer 
wall  of  the  cochlea,  its  sides  by  the  membrane  of  Reissner  and  the 
basilar  membrane  upon  which  rests  the  organ  of  Corti ;  its  blunt  apex 
is  found  at  the  sulcus  spiralis  internus.  Since  these  membranes  ex- 
tend the  entire  length  of  the  bony  spiral  canal  of  the  cochlea,  the 
space  which  is  thus  apparently  cut  off  from  the  scala  vestibuli  must 
form  a  spiral  canal,  included  between  the  scala  tympani  on  the  one  side 
and  the  scala  vestibuli  on  the  other;  this  canal  is  the  scala  media  or 
cochlear  duct. 

The  scala  media  is  an  endolymphatic  canal.  At  the  apex  of  the 
cochlea  it  ends  in  a  blind  extremity  which  is  known  as  the  lagena  or 
cecum  cupulare;  its  opposite  end  forms  a  blind  pouch  between  the  fenes- 
tra  cochleae  and  the  fenestra  vestibuli,  at  the  base  of  the  cochlea,  which 
is  termed  the  cecum  vestibulare.  The  scala  media  is  connected  with 
the  saccule  and  utricle  by  means  of  the  canalis  reuniens,  as  described 
above. 

The  scala  tympani  and  scala  vestibuli,  on  either  side  of  the  scala 
media,  extend  spirally  from  the  base  to  the  apex  of  the  cochlea.  At 
the  apex  they  are  united  by  the  Jielicotrema,  a  continuation  of  these 
canals  which  curves  around  the  hamulus.  At  the  base  of  the  cochlea 
the  two  canals  diverge,  the  scala  tympani  ending  abruptly  at  the  fenestra 
cochleae,  which  is  closed  by  a  fibrous  membrane,  clothed  on  its  tympanic 
surface  by  the  flattened  epithelium  of  the  tympanic  mucosa,  and  on  its 
cochlear  surface  by  the  epithelium  of  the  scala  tympani.  This  secondary 
tympanic  membrane  serves  for  the  relief  of  tension  in  the  cochlea  when 
the  perilymph  is  set  into  motion  by  the  stapes.  The  scala  vestibuli,  on 
the  other  hand,  is  continued  backward  into  the  vestibule,  where  it  is 
in  relation  with  the  external  surface  of  the  saccule  and  utricle,  and, 


704  THE  EAE 

since  it  is  in  contact  with  the  outer  wall  of  the  bony  vestibule,  this  por- 
tion of  the  scala  vestibuli  receives  the  opening  of  the  fenestra  vestibuli, 
which  is  closed  by  the  foot  plate  of  the  stapes.  Corresponding  to  the 
relative  positions  of  the  fenestra  vestibuli  and  fenestra  cochleae,  the  scala 
vestibuli  in  the  first  turn  of  the  cochlea  lies  above  the  scala  tympani, 
and  being  somewhat  the  longer  it  also  extends  farther  backward. 

Having  traced  the  general  form  and  relations  of  the  several  portions 
of  the  cochlea,  we  are  now  in  a  position  to  study  more  carefully  the 
finer  structure  of  its  more  important  parts. 

The  membranous  wall  of  the  scala  tympani  and  scala  vestibuli  is 
alothed  by  a  mesenchymal  epithelium  of  flattened  endothelioid  cells, 
which  rest  upon  a  double  layer  of  fibrous  tissue.  Thus  the  tunica  propria 
also  serves  as  a  periosteum  for  the  inner  surface  of  the  bony  wall  of  the 
cochlea,  and  conveys  the  blood  and  lymphatic  vessels.  The  scalae  are 
perilymphatic  canals.  They  communicate  with  the  subdural  space 
through  the  aqueductus  vestibuli  and  the  aqueductus  cochleae.  The  latter 
opens  from  the  scala  tympani  near  its  beginning  at  the  fenestra  coch- 
leae, and  passes  below  the  pyramid  to  the  dura  transmitting  a  small 
vein. 

The  vestibular  membrane  (of  Reissner)  is  an  extremely  delicate 
structure  which  consists  of  a  thin  central  substantia  propria,  covered 
on  either  surface  by  epithelium,  that  on  the  one  surface  being  con- 
tinuous with  the  mesenchymal  epithelium  of  the  scala  vestibuli,  that 
on  the  other  with  the  ectodermal  epithelium  of  the  scala  media.  It  is 
non-vascular  in  the  adult. 

The  outer  wall  of  the  scala  media  is  lined  by  a  continuation  of  the 
epithelium  in  that  portion  which  adjoins  the  membrane  of  Beissner, 
and  this  rests  upon  a  fibrous  membrane  similar  to  that  which  forms 
the  walls  of  the  other  scalae.  Toward  the  attachment  of  the  membrana 
basilaris,  however,  the  tissue  of  the  outer  fibrous  wall  of  the  scala  media 
is  much  thickened,  and  forms  a  dense  ligamentous  structure,  triangular 
in  shape  as  seen  in  a  longitudinal  section  of  the  cochlea,  which  receives 
the  insertion  of  the  membrana  basilaris  at  its  apex,  and  being,  like 
the  basilar  membrane,  continued  from  the  base  to  the  apex  of  the  cochlea, 
is  known  as  the  spiral  ligament.  Its  dense  fibrous  bands  radiate  from 
the  attachment  of  the  basilar  membrane  to  all  portions  of  the  ligament, 
and  are  firmly  attached  to  the  bony  wall  of  the  cochlea,  with  whose 
periosteum  the  deeper  fibers  of  the  spiral  ligament  are  blended. 

The  surface  of  the  spiral  ligament,  which  forms  the  outer  wall  of 
the  scala  media,  slopes  gradually  away  from  the  attachment  of  the  basilar 


THE  INTERNAL  EAE  705 

membrane;  that  which  impinges  upon  the  scala  tympani  slopes  more 
abruptly.  The  greater  portion  of  the  spiral  ligament,  therefore,  is  con- 
tained within  the  scala  media.  Here  it  is  lined  by  low  columnar  or 
cuboidal  epithelium  whose  cells  blend,  without  demarcation,  with  the 
underlying  vascular  connective  tissue,  so  that  the  minute  blood-vessels 
frequently  appear  as  if  lying  within  the  epithelial  layer,  although  they 
probably  are  always  contained  within  the  connective  tissue  processes 
which  project  into  the  attached  surface  of  the  epithelial  layer. 

This  very  vascular  subepithelial  portion  of  the  spiral  ligament  is 
known  as  the  stria  vascularis.  A  short  distance  above  the  point  of 
attachment  of  the  basilar  membrane  to  the  spiral  ligament  appears  a 
prominent  spiral  ridge,  the  prominentia  spiralis,  the  intervening  groove 
constituting  the  sulcus  spiralis  externus.  The  larger  blood-vessel 
(venous)  within  the  prominence  is  the  vas  prominens.  From  the  ex- 
ternal sulcus  there  extend  into  the  subjacent  ligamentous  tissue  numer- 
ous large  clear  clumps  of  epithelioid  cells.  These  have  been  variously 
interpreted  as  neuro-epithelial  elements  and  as  smooth  muscle  cells. 
But  Shambaugh  (Archives  of  Otology,  37,  6,  1908)  has  shown  that  they 
contain  tubules  which  open  into  the  sulcus,  and  that  they  are  in  reality 
branched  tubular  glands.  He  ascribes  to  them  the  function  of  pro- 
ducing at  least  a  portion  of  the  endolymph  of  the  scala  media ;  the  stria 
vascularis  is  probably  also  an  important  source  of  endolymph. 

The  tympanic  wall  or  floor  of  the  scala  media  presents  for  examina- 
tion several  structures,  which,  from  within  outward  (viz.,  from  the 
modiolus  to  the  ligamentum  spirale),  are  the  limbus  spiralis,  membrana 
tectoria,  sulcus  spiralis  internus,  basilar  membrane,  and  the  organ  of 
Corti  which  rests  upon  the  basilar  membrane  (Fig.  587). 

The  vestibular  lip  of  the  limbus  spiralis  presents  a  distinct  eleva- 
tion, which  is  formed  by  a  peculiar  cellular  variety  of  connective  tissue, 
and  is  covered  by  columnar  epithelium,  whose  cells  are  not  sharply  de- 
fined from  those  of  the  underlying  connective  tissue.  The  surface  of 
the  epithelium  presents  a  distinct  cuticular  formation  of  considerable 
thickness,  which  seems  to  be  prolonged  outward  from  the  margin  of 
the  vestibular  lip,  and  forms  the  membrana  tectoria. 

The  surface  of  the  limbus  spiralis,  when  viewed  from  the  scala 
media,  presents  slight  elevations  which,  at  the  margin  of  the  vestibular 
lip,  are  prolonged  into  prominent  ridges  whose  indented  borders  over- 
luing  the  sulcus  and  are  known  as  the  auditory  teeth  (of  Huschke). 

The  Membrana  Tectoria  (Membrane  of  Corti}.— This  is  an  exo- 
plasmic  or  cuticular  tissue,  formed  by  the  epithelium  of  the  inner  or 


706  THE  EAR 

limbus  portion  of  the  embryonic  cochlear  duct.  It  has  a  gelatinous 
fibrillar  structure,  but  lacks  nuclei ;  and,  unlike  the  otherwise  very  simi- 
lar otolithic  membranes  of  the  macula?  and  cristse,  it  contains  no  calca- 
reous products.  Its  free  margin  overhangs,  or  rests  lightly  upon,  the  hair 
cells  of  Corti's  organ. 

The  tectorial  membrane  has  been  very  carefully  studied  by  llardesty 
(1908)  in  the  pig,  from  whose  cochlea  he  has  been  able  to  remove  it  entire. 
It  is  said  to  measure  about  30  mm.  in  length,  to  occupy  the  four  turns  of 
the  cochlea,  to  be  about  five  times  as  wide  and  five  times  as  thick  in  the 
apical  turn  as  at  the  basal  end,  and  to  have  a  section  area  in  the  apical 
turn  approximately  twenty-one  times  and  a  volume  ninety-five  times  the 
area  and  volume  of  its  basal  end.  It  is  described  as  consisting  'of  a  hyaline 
matrix,  probably  keratin,  in  gelatinous  form,  in  which  are  embedded  the 
very  numerous  fine  fibers  or  threads  of  uniform  size'  (Anat.  Rec.,  8,  2, 
1914).  The  membrane  has  a  slight  amount  of  elasticity,  is  of  a  semi-solid 
character  and  possesses  'marked  adhesiveness';  its  specific  gravity  is  said 
to  be  but  little  greater  than  tliat  of  the  endolymph.  None  of  the  fibers 
extend  the  entire  width  of  the  membrane,  none  are  attached  at  both  ends, 
and  the  greater  number  are  attached  at  neither  end  (Hardesty,  Amer.  Jour. 
Anat.,  8,  2,  1908).  Hardesty  describes  a  stripe  (Hensen's  stripe)  on  the 
under  surface  of  the  tectorial  membrane  opposite  the  row  of  inner  hair 
cells,  which  he  explains  'as  a  line  of  intercrossing  ends  of  fibers  of  the 
under  surface  resulting  from  the  process  by  which  the  growth  of  the  mem- 
brane terminates.'  He  describes  also  a  thin,  exceedingly  delicate,  'acces- 
sory tectorial  membrane,'  along  the  under  surface  of  the  outer  portion  of 
the  chief  membrane;  only  its  outer  edge  is  attached  to  the  latter,  and  it  is 
bounded  internally  by  Hensen's  stripe,  thus  covering  only  the  outer  hair 
cells. 

The  Sulcus  Spiralis  Interims. — This  is  a  deep  groove  included  be- 
tween the  vestibular  lip  of  the  limbus  and  the  basilar  membrane  which 
is  attached  to  the  tympanic  lip.  The  sulcus  is  lined  by  flattened  epi- 
thelial cells,  which  are  apparently  continuous  with  those  of  the  vestib- 
ular lip,  and  like  them  are  not  readily  distinguished  from  the  under- 
lying connective  tissue.  The  epithelium  is  continued  outward  upon  the 
basilar  membrane  to  the  margin  of  Corti's  organ,  with  the  innermost 
cells  of  which  it  is  continuous. 

The  Basilar  Membrane  (Memlrana  basilaris) . — This  is  a  thin  but 
resistant  membranous  structure,  upon  which  rests  the  epithelium  of 
Corti's  organ.  Hardesty  (1908)  describes  it  as  a  'flat  tendon  .  .  .  whose 
purpose  is  merely  to  strengthen  the  floor  of  the  ductus  cochlearis  and 


708  THE  EAE 

the  position  of  the  organ  of  Corti,  and  the  fibers  of  which  are  too  rigid 
and  firmly  associated  to  allow  of  resonant  vibration.'  Its  tympanic  sur- 
face is  clothed  by  a  continuation  of  the  lining  membrane  of  the  scala  tym- 
pani,  consisting  of  a  mesenchymal  epithelium,  resting  upon  a  very  thin 
and  delicate  connective  tissue  layer.  The  substantia  propria  of  the  bas- 
ilar  membrane  consists  of  tendinous  bands  which,  being  radially  disposed, 
span  the  interval  between  the  margin  of  the  tympanic  lip  of  the  osseous 
spiral  lamina  and  the  opposed  margin  of  the  spiral  ligament. 

Because  of  the  great  breadth  of  the  modiolus  at  the  base,  and  its 
rapid  diminution  in  thickness  toward  the  apex  of  the  cochlea,  this 
interval  is  relatively  narrow  at  the  beginning  of  the  first  turn  of  the 
spiral  scala  media,  but  progressively  widens  as  the  apex  of  the  cochlea 
is  approached.  Consequently,  the  shortest  tendinous  fibers  of  the  basilar 
membrane  are  found  at  the  base  of  the  cochlea,  the  longest  at  its  apex. 
The  shortest  fibers  are  also  the  coarsest.  It  has  been  estimated  that 
there  are  24,000  distinct  fibers  or  'auditory  strings'  in  the  basilar 
membrane. 

The  substantia  propria  is  covered  upon  that  surface  which  faces 
the  scala  media  by  a  thin  homogeneous  membrane,  a  cuticular  forma- 
tion or  exoplasmic  derivative,  upon  which  rests  the  epithelium  of  the 
organ  of  Corti. 

The  Organ  of  Corti. — This  organ  consists  of  a  highly  differenti- 
ated neuro-epithelium  whose  specialized  cells  are  disposed  according  to 
a  very  regular  arrangement.  The  flattened  epithelium  of  the  sulcus 
spiralis  internus  is  continued  for  a  short  distance  upon  the  basilar  mem- 
brane. Suddenly,  at  the  margin  of  Corti's  organ,  it  alters  its  char- 
acter. Here  the  epithelium  becomes  abruptly  changed  to  a  tall  columnar 
variety,  the  first  cells,  known  as  the  inner  sustentacular  cells,  being  ap- 
parently piled  upon  one  another  and  resting  against  the  inner  hair  cells, 
which  form  a  single  row  of  neuro-epithelium;  these,  like  all  the  suc- 
ceeding rows  of  cells,  can  be  traced  as  a  continuous  line  in  the  spirally 
wound  scala  media,  from  the  base  to  the  apex  of  the  cochlea. 

The  inner  auditory  or  hair  cells  have  a  broad  body  which  is  con- 
fined to  the  superficial  third  of  the  epithelial  layer  and  which  is  nu- 
cleated at  its  deeper  end.  Its  free  surface  forms  an  expanded  oval 
plate  from  which  about  twenty  stiff  cilia  project  through  a  cuticular 
membrane  toward  the  cavity  of  the  scala  media.  These  end  plates 
interdigitate  with  the  phalanges  of  the  inner  pillar  cells,  which  are  to 
be  shortly  described.  The  bases  of  the  inner  hair  cells  are  thin  and 
slender,  and  are  in  relation  with  a  nerve  plexus  of  fine  fibrils  derived 


THE  INTERNAL  EAK  709 

from  the  terminal  processes. of  the  cochlear  nerve.  These  nerve  fibrils 
make  their  exit  in  small  bundles  from  the  bony  spiral  lamina,  through 
the  foramina  nervosa  and  passing  outward  upon  the  basilar  membrane 
are  distributed  in  a  plexus  beneath  the  epithelium,  some  of  their  naked 
processes  almost  immediately  penetrating  the  epithelial  layer  to  end 
between  the  bases  of  the  inner  hair  cells. 

The  inner  hair  cells  rest  against  the  inner  pillar  cells,  or  rods,  of 
Corti's  arch.  This  arch  is  formed  by  two  rows  of  highly  specialized 
cells,  the  inner  and  the  outer  pillars.,  which  are  widely  separated  where 
their  bases  are  attached  to  the  basilar  membrane,  but  are  in  contact 
at  their  free  ends;  in  fact,  the  free  extremity  of  the  inner  pillar  is  pro- 
longed into  a  broad  flattened  plate-like  process  whose  inner  margin  in- 
terdigitates  with  the  head  plate  of  the  inner  hair  cells,  as  stated  above, 
and  whose  outer  margin  is  so  prolonged  as  to  almost,  though  not  com- 
pletely, cover  the  rounded  head  of  the  outer  pillar.  The  head  of  the 
outer  pillar,  being  similarly  flattened,  expanded,  and  prolonged  outward 
beyond  the  margin  of  the  head  plate  of  the  inner  pillar  cell,  comes  into 
contact  with  the  phalanges  of  Deiters'  cells  and  with  the  cilia  of  the 
outer  hair  cells  which  lie  next  without;  they  leave  a  space  between 
the  outer  pillars  and  the  outer  hair  cells  which  is  known  as  Nuel's  space, 
filled  by  a  semi-fluid  intercellular  substance. 

The  inner  pillar  cells  are  rather  more  numerous  than  the  outer 
— in  the  entire  length  of  the  scala  media,  according  to  Retzius,  there 
are  5,600  of  the  former  to  3,850  of  the  latter — so  that  about  three  of 
the  expanded  head  plates  of  the  inner  pillars  overlap  two  of  the  rounded 
heads  of  the  outer  pillar  cells.  The  arch  formed  by  the  opposed  pillar 
cells,  being  succeeded  by  similar  arches  of  successive  pillars,  forms  a 
continuous  tunnel,  triangular  in  transection,  which  extends  the  whole 
length  of  the  scala  media,  and  is  known  as  the  canal  of  Corti.  This 
canal  is  also  filled  with  a  semi-fluid  substance. 

Each  pillar  cell  is  differentiated  into  two  portions,  the  pillar  proper 
and  the  basilar  cell,  the  latter  containing  the  nucleus.  The  pillar 
presents  a  fibrillar  appearance,  the  fibrils  being  disposed  in  the  long  axis 
of  its  body.  This  portion  of  the  cell  reaches  from  the  basilar  membrane 
to  the  free  surface  of  the  neuro-epithelium. 

The  basal  part  of  the  cell,  the  basilar  cell,  probably  represents  the 
undifferentiated  portion  of  the  primordial  pillar  cell.  It  consists  of  a 
clear,  finely  granular  cytoplasm  and  contains  the  spheroidal  nucleus.  It 
lies  on  that  side  of  the  pillar  which  faces  the  canal  of  Corti,  the  bases 
of  the  opposed  cells  being  expanded  until  they  meet,  thus  forming  a 


710  THE  EAR 

cuticular  floor  for  the  tunnel.  This  uiidifferentiatcd  basilar  portion 
occupies  only  the  deeper  half  of  the  pillar  cell. 

The  outer  hair  cells  form  three  to  five  rows  of  ciliated  cells  which 
are  similar  in  structure  to  the  inner  hair  cells,  and  which  are  sup- 
ported by  the  sustentacular  cells  of  Dciters.  Their  cylindrical  cell 
bodies  occupy  the  superficial  third  of  the  epithelial  layer  and  at  the 
deeper  extremity  present  a  nucleated  enlargement,  beyond  which  they 
are  continued  only  as  an  extremely  slender  basal  process.  The  free 
ends  of  the  outer  hair  cells  present  an  expanded  oval  surface  from  which 
the  hairs  project.  The  outer  hair  cells  are  about  five  times  as  numerous 
as  the  inner,  that  is,  there  are  about  3,GOO  of  the  inner  to  18,000  of 
the  outer  (Waldeyer).  According  to  certain  authorities  the  hair  cells 
lack  the  delicate  basal  process  in  the  adult  condition. 

The  outer  sustentacular  cells  (Deiters'  cells)  are  cylindrical  cells 
whose  expanded  bases  rest  upon  the  basal  membrane  and  whose  distal 
portions  extend  toward  the  surface  between  the  outer  hair  cells.  The 
superficial  portion  of  these  cells,  being  encroached  upon  by  the  broad 
outer  hair  cells,  is  very  slender;  the  broader  basal  portion  occupies  the 
deeper  two-thirds  of  the  neuro-epithelium,  the  spheroidal  nuclei  being 
found  at  the  level  of  the  middle  third.  Each  sustentacular  cell  contains 
a  cuticular  filament  (fiber  of  Eetzius)  which  begins  in  contact  with  the 
cuticle  of  the  basal  membrane,  and  extends  through  the  axis  of  the 
cell  to  its  free  border,  where  it  expands  to  form  a  broad  flattened 
plate  of  peculiar  shape,  known  as  the  phalangeal  process.  These  cuticu- 
lar processes  surround  and  overlie  the  margins  of  the  head  plates  of  the 
hair  cells,  thus  forming  a  reticular  layer  through  the  openings  of  which 
the  cilia  of  the  hair  cells  project. 

The  cells  of  Deiters  are  succeeded  by  the  sustentacular  cells  of 
Hensen.  These  are  tall  columnar  cells  about  eight  rows  broad,  the  inner- 
most of  which  equal  in  height  the  tall  cells  of  the  preceding  type,  but 
which  at  their  outer  border  become  abruptly  shortened.  Here  they  pass 
into  the  cuboidal  cells  of  Claudius,,  and  are  thus  continued  outward  to  the 
spiral  ligament. 

The  nuclei  of  the  cells  of  Hensen  are  found  in  their  superficial 
third,  those  of  the  cells  of  Claudius  in  the  center  of  the  cell.  Beneath 
Hensen's  cells  other  small  nucleated  elements  are  occasionally  found; 
they  give  to  this  layer  somewhat  the  appearance  of  a  two-rowed  epi- 
thelium and  are  known  as  the  cells  of  Bottcher. 

Both  the  cells  of  Hensen  and  those  of  Claudius  are  provided  with 
a  cuticular  margin  which,  with  the  similar  cuticle  of  the  cells  of  Deiters, 


THE  INTERNAL  EAE 


711 


forms  a  continuous,  membranous,  cuticular  layer  known  as  the  lamina 
reticularis.  The  inner  portion  of  this  cuticular  membrane  is  pierced  by 
the  cilia  of  the  three  to  five  rows  of  outer  hair  cells,  as  already  described. 
A  fibrillar  axial  core  is  a  common  feature  of  all  of  the  sustentacular 
elements  of  Corti's  organ.  This  fiber  of  Retzius  becomes  progressively 

A 


FIG.  588. — DIAGRAM  OF  THE  ORGAN  OF  CORTI. 

A,  surface  view,  from  the  direction  of  the  scala  media;  B,  as  seen 
in  section,  profile  view,  a,  the  vestibular  lip  of  the  lamina  spiralis;  b,  margin  of 
same;  c,  sulcus  spiralis  internus;  d,  inner  sustentacular  cells;  e,  inner  hair  cells;  /, 
pillar  cells;  g,  outer  hair  cells  and  phalanges  of  Deiters'  cells;  h,  cells  of  Hensen;  i, 
cells  of  Claudius.  Very  highly  magnified. 

less  pronounced  in  passing  from  the  pillar  cells,  where  it  is  very  highly 
developed,  to  the  cells  of  Claudius,  where  it  is  barely  discernible. 

In  the  above  description  we  have  directed  attention  to  the  appear- 
ance of  transections  of  the  organ  of  Corti.  In  the  study  of  this  organ 
in  the  fresh  condition,  and  occasionally  in  fixed  and  stained  preparations, 
it  is  possible  to  obtain  a  surface  view  of  this  organ  from  the  direction 
of  the  scala  media.  In  such  preparations  the  polygonal  outlines  of  the 
columnar  cells  of  the  limbus  spiralis,  beneath  which  are  the  auditory 
teeth,  are  seen  on  the  outer  side  of  the  attachment  of  Heissner's  mem- 


712  THE  EAE 

brane.  Beneath  the  overhanging  vestibular  lip  of  the  limbus  the  mosaic 
of  large  polygonal  epithelial  cells  of  the  internal  sulcus  comes  into 
view.  At  the  margin  of  the  organ  of  Corti  these  are  exchanged  for  the 
broader  cell  ends  of  the  inner  sustentacular  cells  and  the  adjacent  single 
row  of  inner  hair  cells. 

The  flattened  rectangular  head  plates  of  the  inner  pillar  cells  form 
the  next  row,  the  heads  of  the  outer  pillars  projecting  from  beneath, 
and  extending  beyond  the  heads  of  the  inner  pillar  cells.  These  are  fol- 
lowed by  the  interdigitating  phalanges  of  the  cells  of  Deiters,  which 
enter  into  the  formation  of  the  reticular  membrane,  through  the  feuestra 
of  which  the  cilia  of  the  three  to  five  rows  of  outer  hair  cells  project. 
This  cuticular  membrane  is  continued  outward,  and  beneath  it  are 
successively  seen  the  ends  of  the  cells  of  Hensen,  and  of  the  cells  of 
Claudius. 

THE  ACOUSTIC  NERVE 

The  acoustic  nerve  presents  two  distinct  divisions  both  of  which  are 
sensory,  but  which  differ  greatly  as  regards  their  central  termination. 
They  likewise  differ  in  their  peripheral  distribution.  Within  the  inter- 
nal acoustic  meatus  the  nerve  divides,  each  branch  consisting  of  numer- 
ous bundles.  The  vestibular  (superior  or  anterior)  division  is  supplied 
with  a  ganglion  of  considerable  size,  the  vestibular  ganglion  (of  Scarpa) , 
beyond  which  the  nerve  separates  into  three  branches  which  supply,  re- 
spectively, the  macula  of  the  utricle,  and  the  cristae  of  the  superior  and 
lateral  semicircular  canals,  in  the  neuro-epithelium  of  each  of  which 
their  terminal  fibrils  end  in  relation  with  the  bases  of  the  hair  cells  (Figs. 
582  and  583).  The  remaining  nerve  fibers  which  are  distributed  to  the 
vestibule  are  derived  from  a  branch  of  the  cochlear  (inferior  or  poste- 
rior) division,  and  they  supply  in  a  similar  manner  the  macula  of  the 
saccule  and  the  crista  of  the  posterior  semicircular  canal.  According  to 
Streeter  (Amer.  Jour.  Anat.,  1907),  the  vestibular  nerve  contributes  also 
the  innervation  to  the  posterior  canal  and  to  the  saccule,  the  cochlear 
nerve  supplying  only  the  cochlea. 

The  cochlear  branch  proper,  cochlear  nerve,  enters  the  modiolus, 
where  it  becomes  abruptly  narrowed  by  giving  off  numerous  fine  branches 
which  pass  outward  between  the  layers  of  the  bony  spiral  lamina.  Here 
they  form  a  continuous  spiral  succession  of  small  nerve  trunks,  supplied 
with  many  bipolar  ganglion  cells,  which  collectively  form  the  spiral 
ganglion  (Fig.  586).  They  penetrate  the  margin  of  the  bony  sulcus 
through  the  foramina  nervosa,  a  succession  of  perforations,  in  the  tym- 


THE  INTERNAL  EAR 


713 


panic  lip  of  the  sulcus.  Here  the  nerve  fibers  lose  their  medullary 
sheath  and  come  almost  at  once  into  relation  with  the  inner  hair 
cells.  From  this  point  the  path  of  the  non-medullated  fibers  varies,  most 
of  them  passing  for  some  distance  along  a  spiral  course  through  the 
organ  of  Corti.  One  such  spiral  bundle  is  found  on  the  inner,  and 
another  on  the  outer  side  of  the  inner  pillars,  the  latter  lying  within 
the  canal  of  Corti.  Still  other  fibers,  the  tunnel  fibers,  cross  the  canal 
of  Corti  to  form  a  spiral  plexus  beneath  the  outer  hair  cells  and  the  cells 


/  i'.p.  v.8.     o.p  Z)i       Z>«  Z>»  B. 

FIG.  589. — AXIAL  SECTION  THROUGH  CORTI'S  ORGAN  OF  THE  GUINEA-PIG,  SHOWING 
THE  TERMINAL  NERVE  FIBRILS. 

B,  cells  of  Bottcher;  Dl,  D2,  D3,  three  rows  of  Deiters'  cells;  H,  cells  of  Hensen; 
i.b.,  inner  border  cell;  i.h.,  inner  hair  cell;  i.p.,  inner  pillar  cell;  n,  terminal  branch  of 
the  cochlear  nerve;  o.h.-l,  2,  3,  three  rows  of  outer  hair  cells;  o.p.,  outer  pillar  cell; 
p.,  phalangeal  process  of  the  outer  sustentacular  process.  Very  highly  magnified. 
(After  Held.) 


of  Deiters.     Terminal  fibrils  from  these  spiral  plexuses  end  in  relation 
with  both  the  inner  and  the  outer  hair  cells. 

The  relation  of  the  nerve  cells  of  the  spiral  ganglion  and  the  vestibu- 
lar  ganglion  to  the  termination  of  the  nerve  fibrils  about  the  hair  cells 
of  the  organ  of  Corti,  the  macula?,  and  the  crista?,  is  essentially  the  same. 
The  ganglia  contain  the  cell  bodies  of  the  peripheral  sensory  neurons 
of  the  eighth  cerebral  or  acoustic  nerve.  These  are  bipolar  cells,  of 
which  the  central  process  or  axon  enters  a  medullated  nerve  fiber  of  the 
acoustic  nerve,  while  the  peripheral  process  is  distributed  to  the  hair 
cells  of  the  several  areas  of  specialized  neuro-epithelium,  as  above  de- 
scribed. 

45 


714 


THE  EAE 

THE  VASCULAR  SUPPLY 


Blood  Supply. — The  internal  ear  is  supplied  by  the  internal  audi- 
tory artery,  a  branch  of  the  basilar  artery,  which  enters  the  labyrinth 
along  with  the  acoustic  nerve,  and  at  once  divides  into  two  main  stems, 
the  vestibular  and  the  cochlear  (arteria  cochlearis  communis,  Sieben- 


d  f 

FIG.  590. — SCHEME  OF  THE  VASCULAR  SUPPLY  OF  THE  INTERNAL  EAR. 

C1,  first  turn  of  the  cochlea;  S,  saccule;  Sup.S.C.,  Ext.S.C.,  and  PosLS.C.,  superior, 
external,  and  posterior  semicircular  canals;  U,  utricle.  The  arteries  are  in  heavy 
black,  the  veins  somewhat  lighter;  a,  central  vein,  and  6,  central  artery  of  the  cochlea; 
c,  vestibular  artery;  d,  vestibulocochlear  artery;  e,  arteria  proprise  cochleae;  /,  vena 
aqueductus  cochleae;  g,  vena  aqueductus  vestibuli. 

mann) .  The  vestibular  artery  accompanies  the  branches  of  the  vestibular 
nerve  to  the  saccule,  utricle,  and  semicircular  canals,  supplying  these 
structures  in  the  posterior  portion  of  the  vestibule,  and  forming  a  rich 
plexus  in  the  connective  tissue  of  the  maculae  and  cristse,  and  a  more 
scanty  network  in  the  remaining  portions  of  the  membranous  labyrinth. 
The  cochlear  division  of  the  internal  auditory  artery,  according  to 
Siebenmann,  promptly  subdivides  into  the  cochlear  artery  proper,  which 
appears  as  the  continuation  of  the  vessel,  and  the  vestibulocochlear 


THE  INTEKNAL  EAE  715 

artery,  which  supplies  the  macula  sacculi,  the  posterior  ampulla,  and  the 
adjacent  portions  of  the  utricle  and  posterior  semicircular  canal.  This 
vessel  also  supplies  the  early  portion  of  the  first  turn  of  the  spiral 
cochlea. 

The  true  cochlear  artery  enters  the  modiolus  and  supplies  a  branch 
to  the  remaining  portion  of  the  first  cochlear  turn,  and  a  terminal 
branch  which  passes  as  far  as  the  apex  of  the  cochlea,  distributing  its 


FIG.  591. — SCHEME  OF  THE  VASCULAR  TERMINATIONS  IN  THE  WALL  OF  THE  COCH- 
LEAR CANALS. 

c,  capillary  vessels  in  the  spiral  ligament;  DC,  cochlear  duct  or  scala  media;  d, 
capillaries  in  the  limbus  spiralis;  /,  scala  tympani;  g,  arteriole;  h,  spiral  ganglion; 
i,  vena  spiralis  inferior;  v,  scala  vestibuli;  j,  vena  spiralis  superior.  (After  Bohm 
and  von  Davidoff.) 

branches  to  the  last  two  turns.  All  of  these  vessels  are  characterized 
by  their  peculiarly  tortuous  course.  They  distribute  terminal  branches 
to  the  limbus  spiralis  and  to  the  connective  tissue  of  the  membranous 
scala  vestibuli,  extending  as  far  around  this  canal  as  the  spiral  ligament. 
No  vessels  cross  in  the  basilar  membrane. 

The  veins  collect  the  blood  from  the  limbus  spiralis  and  the  wall  of 
the  scala  tympani  and  form  venous  trunks  within  the  modiolus,  which 
correspond  more  or  less  closely  with  the  arteries.  Two  of  the  cochlear 
radicals  of  the  venous  tributaries  are  important  by  reason  of  their  posi- 
tion and  relative  size:  the  vas  prorninens  of  the  prominentia  spiralis  of 
the  stria  vascularis,  and  the  vas  spiralis  beneath  the  organ  of  Corti. 


716  THE  EAR 

Those  veins  coming  from  the  wall  of  the  scala  tympani  unite  to  form 
superior  and  inferior  spiral  veins  in  the  inner  wall  of  the  scala  tympani. 
These  vessels  chiefly  empty  into  the  vena  aqueductus  cochlea  which 
finds  its  way  through  the  aqueduct  to  the  internal  jugular  vein.  Other 
branches  from  the  interior  of  the  cochlea  unite  to  form  the  central  vein 
of  the  cochlea,  which  becomes  the  chief  radical  of  the  internal  auditory 
vein,  and  thus  enters  either  the  transverse  or  inferior  petrosal  sinus. 

The  veins  from  the  utricle  and  semicircular  canals  mostly  enter  the 
vena  aqueductus  vestibuli,  which  follows  its  aqueduct  to  the  superior 
petrosal  sinus. 

It  will  be  perceived  that  the  blood  has  three  chief  avenues  of  exit  from 
the  labyrinth :  1,  by  the  vena  aqueductus  vestibuli ;  2,  by  the  vena  aque- 
ductus cochlea?;  and,  3,  by  the  internal  auditory  vein.  The  greater 
portion  of  the  blood  pursues  the  second  course  and  thus  finds  its  way  to 
the  internal  jugular  vein,  the  smaller  remainder  entering  the  petrosal 
sinuses  by  one  of  the  other  two  avenues. 

Lymphatics. — The  internal  ear  contains  relatively  few  lymphatic 
vessels  but  is  richly  supplied  with  broad  lymphatic  spaces.  Anastomosing 
vessels  are  found  in  the  periosteum  and  membranous  wall  of  the  laby- 
rinth. These  communicate  with  the  perilymph  spaces  between  the  peri- 
osteum and  the  membranous  wall  in  the  vestibule,  and  with  the  vestibular 
and  tympanic  scalse  in  the  cochlea.  The  perilymphatic  spaces  are  con- 
nected with  the  subdural  space  of  the  meninges  by  means  of  lymphatic 
channels  in  the  aqueductus  cochlea?.  The  perilymph  of  the  vestibule  also 
communicates  with  the  subdural  space  through  vessels  which  follow  the 
sheaths  of  the  nerves. 

The  endolymph  cavities  of  the  several  divisions  of  the  membranous 
labyrinth  communicate  freely  with  one  another;  by  means  of  the  ductus 
endolymphaticus  a  connection  is  also  established  though  the  aqueductus 
vestibuli  with  the  subdural  space,  the  blind  terminal  saccule  of  this 
canal,  the  saccus  endolymphaticus  lying  upon  the  posterior  surface  of 
the  petrous  bone  and  in  contact  with  the  dura  mater. 


FUNCTION  OF  THE  COCHLEA 

The  cochlea  is  the  essential  organ  of  hearing.  The  fundamental  struc- 
ture concerned  in  audition  is  the  spiral  organ  of  Corti.  The  physiology 
of  sound  perception  involves  proximally  the  stimulation  of  the  hair  cells 
of  Corti's  organ  by  the  tectorial  membrane.  This  membrane  is  thrown 


DEVELOPMENT   OF  THE   EAE  717 

into  synchronous  vibrations  by  the  undulations  in  the  endolymph  of  the 
cochlear  duct  transmitted  through  the  vestibular  membrane  from  the  peri- 
lymph.  The  latter  receives  the  sound  waves  through  the  foot-plate  of  the 
stapes. 

The  Helmholtz  (1896)  theory  of  tone  perception,  until  recently  widely 
accepted,  postulated  sympathetic  vibrations,  in  resonance  with  atmospheric 
waves,  on  the  part  of  the  fibers  of  the  basilar  membrane.  This  view  has 
been  shown  to  be  untenable,  notably  by  Shambaugh  (Archives  of  Otology, 
37,  6,  1908)  and  by  Hardesty  (Amer.  Jour.  Anat.,  8,  2,  1908).  The  basilar 
membrane  contains  only  a  little  more  than  half  as  many  fibers  as  the 
maximum  number  of  vibrations  (40,000  double  vibrations  per  second)  com- 
monly audible;  moreover,  it  does  not  possess  the  physical  and  histologic 
properties  demanded  by  the  'resonance  theory'  of  tone  perception.  Har- 
desty has  shown  that  the  tectorial  membrane  on  the  contrary  does  answer 
the  requirements  of  an  alternative  theory,  a  modification  of  the  earlier 
'telephone  theory'  of  Rutherford  (1886)  ;  and  he  has  succeeded  in  construct- 
ing an  apparatus  which  simulates  the  cochlea,  and  imitates  its  presumed 
functional  activity  at  least  in  the  lower  ranges  of  the  tone  scale. 

Hardesty  suggests  'that  notes  up  to  a  certain  pitch  throw  the  entire 
natural  tectorial  membrane  into  vibrations  of  corresponding  frequencies 
and  that  sensations  of  pitch  are  determined  by  the  frequency  of  impinge- 
ment of  the  membrane  upon  the  auditory  hairs,  intensity  being  determined 
by  the  amplitude  and  quality  by  the  quality  of  the  wave  motion  imparted. 
Further,  that  the  highest  notes  within  the  range  of  the  auditory  apparatus 
throw,  according  to  their  frequency,  only  varying  extents  of  the  smaller, 
basal  end  of  the  tectorial  membrane  into  vibration,  being  so  damped  out 
in  passing  toward  the  apex  of  the  cochlea,  overcoming  friction,  the  inertia 
of  the  endolymph  and  that  of  the  membrane  itself,  as  not  to  produce  vibra- 
tions in  the  heavier,  apical  portions.'  (Anat.  Rec.,  8,  2,  1914). 

In  essence,  the  tectorial  membrane  is  conceived  to  respond  in  its  sev- 
eral parts  in  the  manner  of  a  physical  resonator  to  tones  of  different  pitch 
(Shambaugh).  According  to  this  conception,  tone  analysis  is  accomplished 
peripherally,  the  specific  stimulus  being  carried  to  the  brain  by  the  special 
sets  of  cochlear  nerve  fibers. 


DEVELOPMENT  OF  THE  EAR 

The  external  ear  develops  in  connection  with  the  first  branchial  fur- 
row: the  meatus  from  the  deepened  groove,  the  auricle  through  the  fusion 
of  definite  tubercles  on  the  adjacent  branchial  arches. 

The  middle  ear  and  auditory  tube  arise  from  the  corresponding  pharyn- 
geal  pouch,  the  process  involving  a  ventral  elongation  of  the  groove  to  form 


FIG.  592. — SBMIDIAGRAMMATIC  ILLUSTRATIONS  OF  SUCCESSIVE  STAGES  IN  THE  DE- 
VELOPMENT OF  THE  INTERNAL  EAR  OF  THE  CHICK. 

A,  45  hour  embryo;  B,  60  hour  embryo;  C,  5  day  embryo;  D,  7  day  embryo;  M, 
wall  of  neural  canal  at  level  of  metencephalon ;  E,  epidermal  ectoderm ;  op,  otic  pit ; 
oc,  otocyst  (otic  vesicle);  DE,  ductus  endolymphaticus;  SE,  saccus  endolymphaticus; 
cd,  cochlear  duct;  u,  utriculus;  dss,  superior  semicircular  duct;  dsl,  lateral  semi- 
circular duct. 


dss 


FIG.  593. — WAX  RECONSTRUCTIONS  OF  THREE  EARLY  STAGES  IN  THE  DEVELOP- 
MENT OF  THE  INTERNAL  EAR  (MEMBRANOUS  LABYRINTH)  OF  MAN. 

A,  lateral  view,  from  a  6.6  mm.  embryo;  B,  lateral  view  from  an  11  mm.  embryo; 
C,  front  view  from  a  20  mm.  embryo  (A  and  B  correspond  approximately  to  stages 
C  and  D  of  the  preceding  figure).  DE,  ductus  endolymphaticus;  8E,  saccus  endo- 
lymphaticus; VP,  vest ibular  pouch;  cp,  cochlear  pouch;  ap,  absorption  focus;  c, 
eras;  s,  sacculus;  u,  utriculus;  cd,  cochlear  duct;  dss,  dsp,  and  dsl,  superior,  poste- 
rior, and  lateral  semicircular  ducts.  (After  Streeter.) 


718 


DEVELOPMENT  OF  THE  EAR  719 

the  tube  and  a  subsequent  dorsal  dilatation,  expanding  as  the  tympanum 
to  include  the  auditory  ossicles  which  have  meanwhile  taken  form  in  the 
adjacent  mesenchyma.  The  mastoid  cells  are  formed  by  a  late  erosion  and 
invasion  of  the  bone  by  the  mucous  membrane  of  the  tympanum. 

The  internal  ear  develops  from  a  thickening  in  the  epidermal  ectoderm 
at  the  level  of  the  third  primary  cerebral  vesicle.  This  auditory  anlage 
becomes  invaginated  to  form  an  otic  pit,  the  aperture  of  which  subse- 
quently closes  and  thus  separates  an  auditory  vesicle  or  otocyst  from  the 
overlying  parent  ectoderm.  At  the  point  of  closure  medially  a  dorsal 
evagination  arises  to  form  the  endolymphatic  duct.  At  the  upper  pole  of 
the  vesicle  appear  the  semicircular  ducts  through  a  process  involving  the 
elevation  of  three  circular  folds,  the  lateral  walls  of  which  fuse  proximally, 
and  subsequently  disappear  leaving  a  peripheral  duct  dilated  at  one  end 
to  form  an  ampulla.  The  cochlea  arises  at  the  opposite  pole  as  a  tubular 
evagination  which  becomes  spirally  disposed.  The  original  vesicle  persists 
as  the  utricle;  on  its  anteromedial  border  is  formed  an  alveolar  evagina- 
tion, the  saccule,  which  remains  connected  by  a  constricted  duct,  the  utric- 
ulosaccular  canal,  to  which  is  attached  the  ductus  endolymphaticus. 

Each  ampulla  differentiates  an  elongated  patch  of  neuro-epithelium, 
the  cristae;  in  both  utricle  and  saccule  a  similar  oval  patch  appears,  the 
macula;  the  spiral  organ  of  the  cochlea  develops  in  like  manner  through 
a  specialization  of  the  ectoderm  along  the  floor  of  the  membranous  duct. 

The  bony  labyrinth  develops  from  the  mesenchyma  originally  envelop- 
ing the  membranous  labyrinth.  The  mesenchyma  immediately  surround- 
ing the  membranous  labyrinth  becomes  converted  into  a  mucoid  tissue 
which  eventually  disappears,  leaving  the  perilymphatic  spaces;  these  are 
bounded  by  periosteum,  the  innermost  layer  of  which  becomes  modified  into 
a  mesenchymal  epithelium. 

The  scala  tympani  and  scala  vestibuli  of  the  cochlea  are  formed  by 
tin;  coalescence  and  subsequent  dilatation  of  small  mesenchymal  tissue  spaces 
in  two  distinct  regions:  one  between  the  saccule  and  the  oval  window,  the 
other  between  the  saccule  and  the  round  window.  From  these  two  areas  the 
two  great  scala?  of  the  cochlea  proceed  in  a  definite  and  constant  direction 
to  their  definite  position  and  condition  (Streeter,  Proc.  Amer.  Assoc.  Anat., 
1916). 


CHAPTER    XX 
HISTOLOGIC  TECHNIC 

The  satisfactory  examination  of  the  tissues  with  the  aid  of  the  mod- 
ern microscope  requires  certain  preparatory  steps  which  are  in  certain 
cases  very  simple,  in  others  very  complicated.  The  present  chapter  deals 
briefly  with  the  more  important  and  simpler  methods,  and  the  general 
principles  upon  which  they  are  based. 


THE  EXAMINATION  OF  FRESH  TISSUES 

Certain  tissues  may  be  examined  immediately  after  they  have  been 
removed  from  the  body.  This  method  is  applicable  to  blood,  lymph, 
scrapings  from  the  spleen,  liver,  uterus,  and  similar  organs,  small  frag- 
ments of  muscle,  connective  tissue,  etc. 

A  small  drop  of  blood  may  be  collected  upon  the  under  surface  of  a 
cover  glass,  which  is  then  quickly  dropped  upon  a  glass  slide  and 
examined  at  once.  The  glass  must  be  thoroughly  cleaned,  otherwise  a 
thin  preparation  can  not  be  obtained.  Slides  and  covers  should  be 
washed  in  very  dilute  hydrochloric  acid  (about  10  per  cent.),  then 
washed  in  running  water  for  several  hours,  and  finally  rinsed  in  95  per 
cent,  alcohol.  Ordinarily  slides  and  cover  glasses  can  be  sufficiently 
cleaned  by  simply  dipping  in  alcohol  and  drying  with  a  linen  cloth. 

Scrapings  from  the  epithelium  of  the  mouth,  or  from  similar  mucous 
membranes,  may  be  prepared  in  the  same  manner  as  blood,  and  ex- 
amined while  still  suspended  in  their  own  'fluids.  Most  tissues,  however, 
are  not  sufficiently  well  moistened  for  examination  after  this  manner; 
the  preparation  must  then  be  diluted  with  some  inert  fluid.  Normal 
saline  solution  may  be  used  for  this  purpose;  the  following  formula  is 
recommended : 

Sodium  chlorid 0.75  to  0.9  grm. 

Distilled  water 100  c.c. 

720 


THE  DISSOCIATION  OF  TISSUES  721 

Some  histologists  regard  a  0.6  per  cent,  solution  preferable.  Normal 
salt  solution  has  become  quite  generally  displaced  by  Ringer's  Solution, 
which  corresponds  more  nearly  to  blood  plasma  and  is  less  likely  to 
produce  distortion.  This  is  prepared,  adjusted  to  tissues  of  warm- 
blooded animals,  according  to  the  following  formula : 

Sodium  chlorid   90.0 

Potassium  chlorid 4.2 

Calcium  chlorid  (anhydrous)    2.4 

Potassium  bicarbonate 2.0 

Distilled  water  10000.0 

In  order  to  render  the  nuclei  more  conspicuous  a  drop  of  a  5  per 
cent,  aqueous  solution  of  acetic  acid  may  be  added.  This,  however,  will 
dissolve  theo  collagenous  fibers  and  albuminous  granules.  The  nuclei 
may  be  stained  by  the  addition  of  a  drop  of  a  1  per  cent,  aqueous  solu- 
tion of  methylene  blue. 

A  40  per  cent,  solution  of  glycerin  in  distilled  water  also  is  useful 
as  an  examining  medium;  better  still,  the  tissues  may  be  suspended 
in  a  mixture  of  equal  parts  of  95  per  cent,  alcohol,  glycerin,  and  dis- 
tilled water.  This  mixture  is  especially  useful,  for  in  it  tissues  may  be 
kept  for  a  long  period  without  deterioration. 

Amniotic  fluid  obtained  from  pig  fetuses  is  also  valuable  as  a  medium 
for  the  examination  of  fresh  tissues. 

Hogan  (Jour.  Amer.  Med.  Assoc.,  64,  9,  1915)  has  devised  a  normal- 
salt-gelatin  mixture  with  a  colloidal  constitution  like  that  of  blood  serum, 
which  serves  as  a  favorable  indifferent  medium  for  the  examination 
of  fresh  blood  and  other  delicate  tissues.  For  the  method  of  preparation 
reference  should  be  made  to  the  original  article. 


THE  DISSOCIATION  OF  TISSUES 

It  is  frequently  desirable  to  dissociate  tissues  to  a  certain  extent  into 
their  component  elements  prior  to  microscopical  examination.  This  is 
accomplished  by  teasing,  or  by  the  solvent  action  of  relatively  strong 
acids  or  alkalies.  Isolation  by  the  latter  method  is  known  as  maceration. 

For  teasing,  minute  fragments  of  tissue  are  separated  by  the  aid  of 
needles  or  scissors  and  placed  on  a  clean  slide,  where  they  are  to  be 
kept  always  moistened  with  normal  saline  solution  or  other  isotonic 


722  HISTOLOGIC  TECHNIC 

fluid.  For  their  further  manipulation  a  dissecting  microscope  is  useful, 
though  not  essential.  Two  sharply  pointed  needles,  mounted  in  wooden 
handles,  are  to  he  used. 

The  fragment  of  tissue  is  pinioned  with  the  needle  held  in  the  left' 
hand,  and  with  that  in  the  right  the  tissue  is  gently  torn  hy  a  rhythmic 
combing  motion,  being  very  careful  to  avoid  squeezing  the  tissue  between 
the  needle  and  the  slide.  With  a  little  practice  bundles  of  fibers,  groups 
of  cells,  etc.,  are  readily  isolated  sufficiently  to  be  studied  under  moder- 
ate magnification.  During  the  teasing,  the  fragments  of  tissue  should 
be  kept  well  moistened,  and  are  to  be  frequently  inspected  under  low 
magnification  to  determine  the  progress  of  the  operation.  When  satis- 
factorily prepared,  a  cover  glass  may  be  applied,  and  the  preparation 
examined  under  higher  magnification. 

In  applying  a  cover  glass  care  should  be  taken  to  permit  one  edge 
of  the  cover  to  first  touch  the  slide  while  being  held  at  an  angle  of  30 
degrees  to  40  degrees.  If  the  cover  is  then  gently  lowered  into  place,  the 
air  is  forced  out  before  the  advance  of  the  fluid,  and  the  many  air 
bubbles  which  would  otherwise  be  included  are  not  found  in  the  prepara- 
tion. 

The  method  of  teasing  is  particularly  applicable  to  the  study  of  the 
connective,  and  peripheral  nervous  tissues.  Collagenous  fibers,  elastic 
fibers,  fat  cells,  and  nerve  fibers  are  readily  isolated  in  this  way.  If 
desired,  they  may  be  stained  by  the  addition  of  a  drop  of  a  solution  of 
•methyl  green,  picrocarmin,  etc. 

Chemical  Dissociation.— It  is  necessary  to  dissociate  many  tissues 
by  chemical  means,  either  because  of  the  firm  union  of  the  elements 
composing  the  tissue  or  because  they  may  be  too  delicate  and  fragile  to 
withstand  the  mechanical  teasing.  Epithelial  cells,  nerve  cells,  and 
muscle  fibers  are  readily  macerated  in  this  way. 

For  the  dissociation  of  muscle  fibers  small  cubes  (0.25  to  0.5  c.c.) 
are  placed  for  ten  to  thirty  minutes  in  the  following  solution : 

Strong  nitric  acid 100  c.c. 

Potassium  chlorate,  sufficient  to  saturate. 

The  fragments  of  tissue  should  be  handled  with  glass  rods.  After 
some  minutes  they  begin  to  disintegrate  at  the  surface,  and  should  then 
be  transferred  to  running  water,  where  they  are  left  to  wash  from  three 
to  twelve  hours.  The  pieces  of  tissue  are  then  transferred  to  a  mixture 
of  equal  parts  of  alcohol,  glycerin,  and  water,  and  thoroughly  shaken. 


FIXATION  723 

Muscle  fibers  isolated  in  this  way  may  be  kept  for  months  or  even 
years. 

Caustic  potash  (potassium  hydroxid)  is  also  a  valuable  dissociator 
for  muscle  tissue.  The  solution  commonly  used  is  made  by  dissolving 
40  grams  of  the  potash  in  60  c.c.  of  water.  Cardiac  muscle  is  suffi- 
ciently macerated  in  twenty  minutes.  The  tissue  must  then  be  thor- 
oughly washed,  and  may  be  preserved  in  the  alcohol-glycerin  mixture. 

Epithelium  may  be  dissociated  by  teasing  or  by  the  action  of  a  40 
per  cent,  solution  of  potassium  hydroxid,  or  by  means  of  a  10  or  20 
per  cent,  aqueous  solution  of  'lysol,'  and  preserved,  if  desired,  in  the 
mixture  of  alcohol,  glycerin,  and  water. 

Nerve  cells  may  be  isolated  from  the  anterior  horns  of  the  spinal  cord 
or  other  gray  matter  of  the  central  nervous  system  by  teasing.  They 
may  also  be  isolated  by  immersion  in  a  0.2  per  cent,  aqueous  solution 
of  formalin  in  normal  salt  solution  for  two  to  twenty-four  hours,  or  in 
a  0.2  per  cent,  aqueous  solution  of  potassium  bicarbonate,  two  to  five 
days.  Afterward  they  are  transferred  to  a  normal  saline  solution  or  to 
a  mixture  of  alcohol,  glycerin,  and  water,  and  isolated  by  shaking, 
assisted,  if  necessary,  by  gentle  teasing. 

Similar  preparations  may  also  be  made  by  placing  small  fragments 
of  tissue  in  30  per  cent,  alcohol  (TJanvier's  alcohol;  2  parts  water,  1 
part  95  per  cent,  alcohol)  for  two  days  or  more;  then  shake  thoroughly, 
allow  the  debris  to  settle,  remove  a  drop  of  the  fluid  with  a  pipette,  and 
examine. 

For  the  isolation  of  the  elements  of  the  epidermis,  hair  and  nails, 
stronger  solutions  are  required.  Concentrated  sulphuric  acid  may  be 
employed.  After  maceration  is  complete,  the  cells  must  be  thoroughly 
washed  in  water  and  may  then  be  preserved  in  the  alcohol-glycerin 
mixture.  A  caustic  potash  solution,  acting  for  two  to  three  hours,  is 
also  serviceable  with  these  tissues. 

Any  of  the  above  preparations  may  be  stained  by  the  addition  of  a 
small  drop  of  a  solution  of  cosin,  picrocarmin,  or  methyl  green  to  the 
fluid  in  which  they  are  examined. 


FIXATION 

For  the  preservation  of  tissue,  and  as  a  preparation  for  further 
manipulation,  most  tissues  require  to  be  'fixed.'  Innumerable  formulas 
have  been  advocated  for  this  purpose,  many  of  them  having  as  their 


724  HISTOLOGIC  TECHNIC 

object  the  demonstration  of  certain  structural  features  by  the  after  ap- 
plication of  special  staining  methods. 

The  action  of  the  fixing  fluids  is  in  most  cases  dependent  upon  the 
combination  of  the  reagent  with  the  chemical  elements  of  which  the 
tissue  consists;  very  elaborate  compounds  are  thus  formed. 

The  distinction  between  a  physical  and  a  chemical  combination  of 
a  dye  with  particular  tissue  elements  must  be  emphasized. 

The  following  reagents  are  recommended  for  general  use.  The  choice 
of  a  fixative  is  in  great  measure  determined  by  the  staining  method 
which  is  to  be  afterward  applied. 

Alcohol. — This  is  especially  useful  for  the  fixation  of  the  glandular 
organs.  Tissue  may  be  placed  directly  in  95  per  cent.,  or  in  absolute 
alcohol.  The  fluid  is  to  be  changed  in  twenty-four  hours,  and  again  in 
five  to  seven  'days.  This  method  of  fixation  is  desirable  for  after-staining 
of  the  nervous  tissues  with  methylene  blue  and  for  the  demonstration 
of  glycogen  in  the  hepatic  cells,  cartilage,  etc.  Alcohol  causes  consider- 
able distortion  of  the  internal  architecture  of  the  cell  by  its  rapid  and 
forceful  diffusion  from  the  surface  toward  the  center  of  the  tissue,  the 
cytoplasmic  granules  often  being  in  this  way  forced  to  one  side  of  the 
cell.  This  result  may  be  partially  avoided  by  the  use  of  ' graded  alcohol/ 
viz.,  67  per  cent,  alcohol  for  three  to  twelve  hours,  82  per  cent,  for 
twenty-four  hours,  and  finally  95  per  cent,  alcohol,  which  should  be  once 
changed  after  a  few  days.  Glycogen,  however,  is  partially  dissolved 
by  the  action  of  the  dilute  alcohols. 

The  graded  alcohols  may  be  derived  from  the  95  per  cent,  stock 
supply  by  the  following  dilutions: 

95  per  cent,  alcohol,  1  part;  distilled  water,  1  part=48  per  cent. 
95  per  cent,  alcohol,  3  parts;  distilled  water,  1  part=67  per  cent. 
95  per  cent,  alcohol,  5  parts;  distilled  water,  1  part=82  per  cent. 

For  practical  purposes  these  grades  may  be  regarded  as  50,  70  and  80 
per  cent,  respectively;  they  may  be  derived  also  by  the  use  of  the  fol- 
lowing formula: 

265  c.c.  95%  ale.  +  235  c.c.  aq.  dist.  =  5Q%  ale. 
370  c.c.  95%  ale.  +  130  c.c.  aq.  dist.  =  70 %  ale. 
425  c.c.  95%  ale.  +  75  c.c.  aq.  dist.  =  80%  ale. 

The  distortion  from  the  use  of  strong  alcohol,  as  well  a^  the  disso- 
ciation which  follows  the  use  of  the  weaker  strengths,  may  also  be  par- 


FIXATION  725 

tially  avoided  by  the  addition  of  a  little  iodin  to  the  stronger  alcohol, 
or  by  combination  with  acetic  acid,  thus: 

Glacial  acetic  acid 5  c.c. 

95  per  cent,  alcohol  60  c.c. 

Distilled  water 35  c.c. 

After  fixation  for  three  to  twenty-four  hours  the  tissues  are  washed, 
and  hardened  by  immersion  for  twenty-four  hours  in  each  strength  of 
graded  alcohol  (50,  70,  80  and  95  per  cent),  and  may  be  kept  indefinitely 
in  80  per  cent,  alcohol.  Tissues  should  always  be  stored  in  80  per  cent, 
alcohol.  Lower  grades  tend  to  macerate,  higher  grades  to  harden  unduly. 

Carnoy  recommends  also  a  mixture  of  glacial  acetic  acid  and  abso- 
lute alcohol  in  the  proportion  of  1  to  3 ;  this  gives  excellent  results  with 
muscular  tissues. 

Tissues  for  fixation  by  these  or  any  subsequent  method  are  pref- 
erably cut  into  small  cubes;  a  size  not  exceeding  0.5  to  1  cm.  is  most 
desirable.  If  larger  pieces  of  tissue  are  necessarily  used,  the  reagents 
will  each  require  increased  time  to  insure  complete  penetration. 

Mercuric  Chlorid  (Corrosive  Sublimate}. — This  salt  is  to  be  used  in 
saturated  aqueous  solution.  As  it  dissolves  with  difficulty  in  cold  water, 
the  use  of  a  hot,  normal  saline  solution  hastens  the  operation. 

Mercuric  chlorid  is  an  excellent  fixative  for  cytoplasm,  but  gives  still 
better  results  when  combined  with  a  nuclear  fixative  such  as  acetic  acid. 
The  following  is  an  excellent  method  for  general  use: 

Mercuric  chlorid   7  grm. 

Sodium  chlorid    0.75  grm. 

Distilled  water 95.0  c.c. 

Just  prior  to  use  add  5  c.c.  of  acetic  acid. 

Small  pieces  of  tissue  remain  in  this  corrosive  acetic  mixture  for 
two  to  twenty-four  hours,  and  are  then  transferred  to  graded  alcohol, 
beginning  with  70  per  cent,  and  remaining  twenty-four  hours  in  each 
strength.  Most  dyes  will  act  perfectly  on  tissue  fixed  in  this  way.  If, 
however,  the  presence  of  mercury  interferes  with  the  action  of  a  dye, 
this  salt  can  be  readily  removed  by  the  addition  of  a  few  crystals  of 
iodin  to  the  higher  grades  of  the  graded  alcohols,  renewing  the  iodin  if 
necessary  until  it  is  no  longer  decolorized. 

Formalin.— Tissues  may  be  fixed  in  formalin  (formol),  a  40  per 


726  HISTOLOGIC  TECHNIC 

cent,  solution  of  formaldehyd  gas,  which  is  to  be  used  in  strengths  vary- 
ing from  5  to  20  per  cent.  Small  pieces  should  be  left  in  the  weaker 
solutions  (5  to  10  per  cent.)  from  six  hours  to  two  days,  not  longer. 
In  the  stronger  solutions  (10  to  20  per  cent.)  tissues  should  remain 
for  only  two  to  six  hours.  More  prolonged  immersion  in  the  fixative 
causes  considerable  swelling.  As  a  rule,  the  stronger  solutions  are  pref- 
erable; this  is  especially  true  for  the  fixation  of  the  cells  of  lymphoid 
tissue.  The  10  per  cent,  formalin  solution  is  valuable  for  the  fixation  of 
human  embryos.  For  the  hardening  of  nervous  tissues,  also,  the  10  per 
cent,  solution  is  very  serviceable. 

After  fixation,  the  tissues  are  transferred  directly  to  80  per  cent, 
alcohol,  with  one  or  several  changes.  This  method  gives  excellent  re- 
sults with  lymphoid  and  epithelial  tissues,  but  does  not  bring  out  the 
finer  details  of  cytoplasmic  structure. 

Potassium  Bichromate  (Dichromate) . — This  salt  has  been  used  in 
all  sorts  of  combinations;  those  which  follow  may  be  specially  recom- 
mended. Miiller's  solution  is  employed  for  the  fixation  of  the  tissues 
of  the  central  nervous  system,  and  must  be  used  when  fixation  is  to  be 
followed  by  any  of  the  Weigert  hematoxylin  staining  methods.  Applied 
to  the  fixation  of  other  organs,  Miiller's  fluid  is  apt  to  produce  some 
maceration  and  better  results  are  usually  obtained  with  Miiller-formol  or 
with  Tellyesniczky's  solution. 

For  the  special  fixation  of  cytoplasmic  granules,  and  also  for  after- 
staining  with  Mallory's  connective  tissue  stains,  Zenker's  solution  yields 
better  results. 

Miiller's  Solution: 

Potassium  bichromate 2.5  grm. 

Sodium  sulphate  1.0  grm. 

Water 100.0  c.c. 

Pieces  of  tissue  are  left  in  the  fluid  for  one  to  six  weeks;  large 
pieces  of  the  spinal  cord  or  brain  require  four  to  six  weeks.  If  left  too 
long  the  tissues  will  become  brittle.  After  fixation,  the  tissue  is  washed 
thoroughly  in  running  water  for  twelve  to  twenty-four  hours,  and 
hardened  in  graded  alcohol. 

A  relatively  large  volume  of  the  fixing  fluid  should  be  used,  and 
it  should  be  frequently  changed.  It  should  not  be  allowed  to  become 
turbid  nor  to  deposit  crystals:  this  is  avoided  by  frequent  changes  and 
by  keeping  the  jars  in  the  dark,  or  at  least  in  such  a  position  that 
they  are  not  exposed  to  a  bright  light. 


FIXATION  727 

Tellyesniczky's  Fluid: 

Potassium  bichromate   3  grm. 

Water 100  c.c. 

Glacial  acetic  acid  (added  just  before  use) 5  c.c. 

Pieces  of  tissue  are  placed  in  a  considerable  volume  of  the  fixing 
fluid  and  left  for  three  to  seven  days.  They  are  then  washed  in  run- 
ning water  for  twelve  to  twenty-four  hours,  and  hardened  in  graded 
alcohol.  (Where  tissues  are  first  washed  in  water,  the  graded  alcohols 
must  begin  with  the  50  per  cent,  strength.)  This  fluid  yields  excellent  re- 
sults with  muscular  and  glandular  tissues,  and  is  particularly  serviceable 
where  pieces  of  considerable  size  must  be  used,  e.g.,  whole  embryos. 

Orth's  Fluid    (Miiller-formol)  : 

Miiller's  fluid  95  to  90  c.c. 

Pure  formalin   5  to  10  c.c. 

This  is  an  excellent  fixative  for  general  use,  for  by  it  most  tissues 
are  well  preserved.  Small  pieces  of  tissue  are  left  in  a  considerable 
volume  of  the  fluid  for  one  to  five  days,  washed  thoroughly  in  running 
water  for  twelve  to  twenty-four  hours,  and  hardened  in  graded  alcohol. 
The  washing  should  be  so  thorough  as  to  remove  all  excess  of  the 
chromium  compounds,  otherwise  difficulty  will  be  experienced  in  obtain- 
ing satisfactorily  stained  preparations. 

Chrom- Acetic-Formalin  Mixture. — This  makes  an  excellent  fixing 
fluid  for  general  embryologic  work. 

Mix  and  keep  in  stock  the  following  solution : 

1  per   cent,   chromic   acid    16  volumes 

Glacial  acetic  acid   1  volume 

At  the  time  of  using  add  to  2  volumes  of  the  stock  mixture,  1  volume 
of  formalin. 

Wash  in  water  from  twenty  minutes  to  two  hours  according  to  size. 
Zenker's  Solution: 

Potassium  bichromate    2.5  grm. 

Sodium  sulphate   1.0  grm. 

Mercuric  chlorid   5.0  grm. 

Distilled  water   100.0  c.c. 

Just  prior  to  use  add  1  c.c.  of  glacial  acetic  acid  to  each  20  c.c.  of  the 
fluid. 


728  HISTOLOGIC  TECHNIC 

Small  pieces  of  tissue,  only,  should  be  used.  They  remain  in  a  con- 
siderable volume  of  the  solution  for  three  to  twenty-four  hours,  after 
which  they  are  thoroughly  washed  in  running  water  for  twelve  to 
twenty-four  hours,  and  hardened  in  graded-  alcohol.  The  corrosive 
sublimate  deposits  crystals  in  the  tissue.  These  may  be  removed  by  the 
addition  of  a  crystal  of  iodin  (or  tincture  of  iodin)  to  the  stronger  alco- 
hols until  decolorization  no  longer  occurs.  If  the  mercury  is  not  thus 
removed  it  will  be  difficult  to  obtain  well  stained  specimens,  and  the 
presence  of  the  crystals  may  cause  much  confusion.  In  obstinate  cases 
Lugol's  solution  is  recommended  in  place  of  tincture  of  iodin  (alcoholic 
solution  of  iodin),  to  be  added  until  the  alcohol  has  a  'port  wine'  color. 
(See  page  758.) 

This  is  probably  the  best  fixing  fluid  for  general  routine  histologic 
work.  The  presence  of  the  acetic  acid,  however,  dissolves  the  more  deli- 
cate albuminous  granules.  To  avoid  this,  formalin  may  be  substituted 
in  the  same  proportion,  and  added  in  the  same  way,  for  the  acetic  acid. 
This  modified  Zenker's  fluid  (KELLY'S  FLUID)  is  particularly  valuable 
for  the  preservation  of  tissues  where  it  is  desired  to  investigate  the 
granular  cytoplasmic  contents,  e.g.,  blood  cells  in  embryos,  etc. 

Flemming's  Fluid  (strong  solution)  : 

Chromic  acid,  1  per  cent,  aqueous  solution 15  parts 

Osmic  acid,  2  per  cent,  aqueous  solution 4  parts 

Glacial  acetic  acid 1  part 

The  mixture  should  be  newly  made,  from  stock  solutions  of  the 
ingredients,  immediately  before  using.  The  stock  mixture  undergoes  a 
deteriorating  chemical  transformation. 

Pieces  of  tissue  should  not  be  more  than  2  to  3  mm.  in  thickness 
and  should  be  left  in  the  solution  and  kept  in  the  dark  for  one  to  twenty- 
four  hours,  according  to  the  results  desired.  For  mere  fixation  a  short 
immersion  is  sufficient;  for  blackening  fat  and  the  myelin  of  medullated 
nerve  fibers  the  longer  period  is  necessary.  After  fixation  the  tissues 
are  to  be  washed  in  running  water  for  three  to  twenty-four  hours,  and 
hardened  in  graded  alcohol. 

This  fluid  gives  splendid  results  for  the  fixation  of  the  finer  cyto- 
logical  elements  of  glandular  epithelium;  and  for  the  demonstration 
of  nuclear  constitution,  chromosomes,  and  mitotic  figures,  it  is  unex- 
celled. It  serves  also  to  demonstrate  the  presence  of  fat  and  myelin, 
which  are  blackened  by  the  osmium  tetroxid.  When  used  for  the  dem- 
onstration of  fat  in  sections,  chloroform  should  be  substituted  for 


FIXATION  729 

xylol  in  the  embedding  process.  It  does  not  penetrate  the  tissues  very 
readily,  and  the  surfaces  of  the  piece  are  usually  destroyed  by  over- 
fixation. 

Kleinenberg's  Fluid: 

Saturated  aqueous  solution  of  picric  acid 99  c.c. 

Sulphuric  acid    1  c.c. 

Shake  well,  filter  and  dilute  the  filtrate  with  200  c.c.  of  distilled  water. 

Small  pieces  of  tissue  should  be  left  in  the  fluid  for  about  three 
hours  and  then  transferred  to  70  per  cent,  alcohol,  which  is  changed 
two  or  three  times  during  the  first  day.  Hardening  is  continued  in 
80  and  95  per  cent,  alcohols,  which  are  to  be  frequently  changed.  The 
picric  acid  will  be  slowly  dissolved  by  the  alcohol,  but  will  not  be  en- 
tirely removed  even  after  a  considerable  time;  a  trace  does  no  harm. 

This  fluid  gives  excellent  results  with  small  pieces  of  embryonic 
tissue,  and  possesses  the  additional  advantage  of  removing  the  calcareous 
salts  from  partially  calcified  bone;  it  is  not,  however,  a  strong  decalcify- 
ing reagent. 

When  a  fixative  is  employed  which  contains  picric  acid,  the  tissue 
must  never  be  washed  in  water,  but  is  transferred  directly  to  70  per 
cent,  alcohol. 

Bouin's  Fluid: 

Picric  acid,  saturated  aqueous  solution 75  c.c. 

Formalin    20  c.c. 

Glacial  acetic  acid 5  c.c. 

Small  pieces  of  tissue  are  fixed  from  three  to  twelve  hours,  trans- 
ferred to  70  per  cent,  alcohol,  and  then  passed  through  the  higher 
grades.  This  is  an  excellent  fluid  for  the  fixation  of  embryonic  ma- 
terial. For  chromosome  studies  it  is  probably  surpassed  only  by  Flem- 
ming's  fluid. 

Van  Gehuchten's  Fluid  (Camay's  fluid,  No.  I)  : 

Absolute  alcohol   60  c.c. 

Chloroform    30  c.c. 

Glacial  acetic  acid 10  c.c. 

Very  small  pieces  of  tissue  should  be  used.     They  should  be  left  in 
the  fluid  three  to  twelve  hours,  and  the  vessel  tightly  closed  to  prevent 
evaporation  of  the  volatile  fluid.     The  tissues  are  then  transferred  to 
46 


730  HISTOLOGIC  TECHNIG 

several  changes  of  absolute  alcohol  to  remove  the  fixing  fluid  and  com- 
plete the  dehydration. 

This  fluid  is  especially  valuable  for  the  fixation  of  lung  tissue.  It 
can  be  advantageously  applied  only  to  perfectly  fresh,  viz.,  living  tissues. 

Gilson  discovered  that  this  fluid  could  be  advantageously  modified 
for  cytologic  purposes  by  saturation  with  mercury  bichlorid.  About  20 
grams  should  be  added  to  the  above  mixture.  As  thus  modified  the 
solution  is  commonly  known  as  Carnoy's  fluid,  No.  II.  Its  penetrating 
properties  are  very  high  and  the  degree  of  fixation  delicate.  Tissues 
should  not  be  left  in  the  fluid  for  more  than  an  hour.  The  after- 
treatment  is  the  same  as  with  the  simple  solution,  except  that  tincture  of 
iodin  must  be  used  with  the  alcohols. 

Gilson 's  Fluid     (Mer -euro-nitric  mixture)  : 

Bichlorid  of  mercury    5  grm. 

Nitric  acid  (approximately  80  per  cent.) 4  c.c. 

Glacial  acetic  acid  1  c.c. 

Alcohol  (70  per  cent.) 25  c.c. 

Distilled  water 250  c.c. 

Fix  small  pieces  of  tissue  from  three  to  twelve  hours,  transfer 
directly  to  70  per  cent,  alcohol,  and  pass  through  the  higher  grades, 
with  the  addition  of  tincture  of  iodin.  This  fluid  has  a  high  degree 
of  penetration,  and  produces  faithful  and  delicate  fixation. 

Heat. — This  is  a  useful  agent  for  the  fixation  of  blood,  marrow 
cells,  and  scrapings  from  glandular  and  other  organs,  which  are  not 
to  be  afterward  stained  with  methylene  blue  or  its  compounds.  For 
this  purpose  smears  made  upon  glass  slides  or  cover  glasses  are  quickly 
dried  in  the  air,  heated  to  110  degrees  C.  for  twenty  to  thirty  minutes, 
and  are  then  ready  for  immediate  staining. 

The  smears  are  made  in  the  following  manner:  Slides  or  cover 
glasses  should  be  thoroughly  cleaned  with  a  final  rinsing  in  equal  parts  of 
absolute  alcohol  and  ether.  A  small  drop  of  blood  or  other  fluid  is 
collected  by  quickly  touching  the  center  of  a  cover  glass  to  a  drop  of 
ordinary  size.  This  cover  glass  is  then  immediately  dropped  upon  the 
surface  of  a  second  one,  and  the  two  are  drawn  apart  by  a  rapid  sliding 
motion,  the  two  surfaces  being  maintained  parallel  to  one  another  during 
the  motion.  The  success  of  the  maneuver  depends  upon  its  rapidity,  and 
to  obtain  very  thin  preparations  some  little  dexterity  is  required." 

Fairly  good  smears  are  more  easily  made  with  slides.  A  drop  of  blood 
is  collected  upon  the  end  of  one  glass  slide  whose  edge  must  have  been 


DECALCIFICATION  731 

ground.  The  end  of  the  slide  with  the  drop  of  blood  is  then  touched  to 
the  middle  of  a  second  slide,  the  drop  spreads  out  between  the  two,  and 
the  first  slide  is  rapidly  drawn  over  the  surface  of  the  second,  while 
being  held  at  an  angle  of  about  45  degrees.  A  broad  smear  is  thus 
left  upon  the  surface  of  the  second  slide,  some  portions  of  which  are 
sufficiently  thin,  other  portions  too  thick  for  use.  Like  the  former 
maneuver  the  success  of  this  depends  upon  rapidity,  cleanliness,  and  the 
use  of  a  sufficiently  small  drop  of  fluid. 

Fixation  by  Vapors. — Smears  of  fluids  or  very  thin  pieces  of  tissue 
may  be  fixed  by  a  very  brief  exposure  to  the  vapor  of  osmium  tetroxid, 
formalin,  etc.  This  method  is  only  useful  iii  occasional  instances.  Os- 
mium tetroxid  vapor  has  been  shown  to  preserve  faithfully  the  mito- 
chondria in  young  cells  from  tissue  cultures  (M.  B.  and  W.  H.  Lewis, 
Amer.  Jour.  Anat.,  17,  3,  1915). 

In  all  methods  of  fixation  where  pieces  of  tissue  are  immersed  in 
the  fixing  and  hardening  fluids,  it  is  desirable  to  prevent  the  distortion 
of  the  object  from  the  pressure  of  contact  with  the  glass  container. 
This  is  accomplished  by  suspending  the  object  by  means  of  a  thread,  or 
by  resting  the  tissue  upon  a  thin  layer  of  cotton  placed  in  the  bottom  of 
the  jar. 

DECALCIFICATION 

Tissues  containing  bone  or  other  calcareous  material  require  decalci- 
fication  before  they  can  be  sectioned  for  examination.  If  the  calcareous 
deposit  is  limited  in  amount,  as  in  early  fetal  tissues,  this  can  be  ac- 
complished and  the  tissue  fixed  at  the  same  time  by  the  use  of  Kleiuen- 
berg's  fluid,  a  saturated  aqueous  solution  of  picric  acid,  or  a  5  to  10 
per  cent,  aqueous  solution  of  sulphurous  acid,  the  tissues  being  per- 
mitted to  remain  in  the  decalcifying  fluid  until  a  needle  or  slender  scal- 
pel can  be  readily  pushed  to  the  most  central  portions  without  producing 
great  resistance  or  any  grating  sensation. 

For  well  developed  and  mature  bones  the  above  methods  are  in- 
sufficient, and  stronger  acids  must  be  relied  upon.  Nitric  acid  is  the 
one  most  generally  used  for  this  purpose.  The  tissue  should  have  been 
previously  fixed,  Muller-formol,  Zenker's  fluid,  or  mercuric  chlorid  being 
the  preferable  fixatives.  The  fixed  and  washed  tissues  are  placed  in  2 
to  5  per  cent,  nitric  acid,  and  the  fluid  changed  daily  until  decalcifi- 
cation  is  complete.  They  are  then  thoroughly  washed  in  running  water 
for  twelve  to  twenty-four  hours  and  hardened  in  graded  alcohol. 


732  HISTOLOGIC  TECHNIC 


INJECTION 

Injection  is  used  either  for  the  rapid  dissemination  of  fixing  fluids 
through  whole  organs,  embryos,  etc.,  or  for  the  demonstration  of  blood 
or  lymphatic  vessels.  For  the  former  purpose  mercuric  chlorid  is  the 
most  useful  fixative,  since  it  may  be  immediately  followed  by  the  in- 
jection of  a  hardening  fluid,  alcohol,  by  which  the  remaining  mercury 
is  dissolved  out  of  the  tissue  before  overfixation  occurs.  For  the  latter 
purpose  a  colored  fluid,  either  aqueous  or  gelatinous,  is  forced  into  the 
blood  or  lymphatic  vessels.  Berlin  blue,  carmin,  vermilion,  and  lamp- 
black are  the  coloring  matters  most  frequently  used.  The  last  two 
merely  require  suspension  in  a  gelatinous  or  an  aqueous  menstruum; 
the  preparation  of  Berlin  blue  and  carmin  is  somewhat  more  com- 
plicated. 

Berlin  Blue  Gelatin  Mass: 

Saturated  aqueous  solution    (1  to  20)    of 

Berlin'  blue  (Griibler's) 100  c.c. 

Pure  French  gelatin  (in  sheets) 5  to  10  grm. 

The  gelatin  should  be  quickly  washed  to  remove  dust,  etc.,  and  then 
placed  for  several  hours  in  a  very  little  distilled  water  until  it  becomes 
swollen  and  soft.  The  superfluous  water  is  then  poured  off,  and  the 
gelatin  melted  over  a  water  bath.  The  warmed  solution  of  Berlin  blue 
may  now  be  added,  a  little  at  a  time,  and  continuously  stirred.  Finally, 
the  mixture  is  filtered  through  cotton  flannel  (or  flannel)  which  has 
been  previously  wrung  out  of  hot  water.  If  the  mass  is  not  to  be  used 
at  once,  a  few  crystals  of  thymol  may  be  added  as  a  preservative,  or, 
after  cooling,  a  little  methylic  alcohol  may  be  floated  upon  the  surface  of 
the  solidified  mass.  It  is  better  to  use  it  at  once. 
Carmin  Gelatin  Mass: 

Carmin  (Griibler's) 3  grm. 

Ammonium  hydrate,  strong 6  c.c. 

Pure  French  gelatin 7  grm. 

Distilled    water 80  c.c. 

The  gelatin  is  prepared  and  melted  as  above,  50  c.c.  of  the  water  being 
used,  and  the  evaporation  replaced.  The  carmin  is  rubbed  up  in  a 
mortar  with  the  remaining  30  c.c.  of  the  water,  and  the  ammonia  is 
added  to  render  the  carmin  soluble.  The  mixture  is  now  permitted  to 


HARDENING  733 

stand  for  two  hours,  after  which  it  is  neutralized  by  the  gradual  addi- 
tion of  4  to  6  c.c.  of  glacial  acetic  acid,  the  mixture  being  constantly 
stirred,  and  the  latter  portions  of  the  acid  diluted  with  four  volumes 
of  distilled  water,  and  added  drop  by  drop.  The  acid  soon  changes  the 
color  of  the  mixture  from  a  purplish  carmin  to  a  bright  crimson.  Care 
should  be  taken  not  to  add  too  much  acid.  When  properly  prepared, 
the  sense  of  smell  should  detect  both  ammonia  and  acetic  acid,  and  the 
fluid  should  have  a  dark  crimson  color  (the  addition  of  too  much  acid 
produces  a  brighter  crimson).  Should  the  mixture  be  slightly  over- 
acidified  a  few  drops  of  diluted  ammonia  will  restore  the  proper  con- 
dition. The  carmin  solution  is  now  added  to  the  gelatin  mass,  a  little 
at  a  time  and  with  constant  stirring,  and  the  whole  is  filtered  through 
cotton  flannel  wrung  out  of  hot  water. 

The  gelatin  mass  may  be  kept  for  a  short  time  by  being  covered 
with  methylic  alcohol,  but  is  better  used  at  once. 

The  pressure  required  for  injection  may  be  obtained  by  the  gentle 
use  of  a  hand  syringe;  by  the  displacement  of  the  confined  air  in  a 
large  bottle  or  carboy  by  tap  water;  or  much  better  by  the  use  of  a 
water  blast,  of  which  the  small  glass  type  is  relatively  inexpensive  and 
will  furnish  a  pressure  for  injection  about  equal  to  180  mm.  of  mercury. 
The  air  outflow  of  the  water  blast  is  connected  by  rubber  tubing  with 
a  glass  canula  of  proper  size  to  fit  the  vessel  injected,  a  Wolff  bottle 
containing  the  warm  injection  mass  being  interposed.  If  a  manometer 
is  connected,  by  means  of  a  T -canula,  on  the  proximal  side  of  the 
Wolff  bottle,  a  relatively  even  and  accurately  measured  pressure  is 
assured.  The  amount  of  pressure  should  be  at  first  low  (20  to  40 
mm.  of  mercury),  and  should  be  gradually  increased  up  to,  but  not 
much  beyond,  the  normal  blood  pressure  in  the  vessel  injected. 

The  injected  organ  is  cooled  rapidly  in  a  refrigerator,  or  by  being 
packed  in  ice  or  immersed  in  ice  water.  After  solidification  small  pieces 
are  immediately  placed  in  95  per  cent,  alcohol  for  fixation,  dehydration, 
and  hardening. 

HARDENING 

After  proper  fixation  nearly  all  tissues  require  to  be  further  hardened 
before  satisfactory  sections  can  be  cut.  This  is  accomplished  by  im- 
mersion in  alcohol  until  dehydration  is  complete.  The  process  requires 
from  a  day  to  a  week,  according  to  the  size  of  the  tissue  and  the  volume 
and  strength  of  the  fluid.  Various  strengths  of  alcohol  are  advised.  For 


734  HISTOLOGIC  TECHNIC 

general  use  the  procedure  recommended  by  Gage  ("The  Microscope") 
is  found  to  be  very  satisfactory.  The  tissues  after  fixation  are  suc- 
cessively placed  for  one  or  two  days  in  each  of  the  following  strengths 
of  alcohol — 70,  80  and  95  per  cent.  They  are  then  returned  to  80  per 
cent,  alcohol,  where  they  may  remain  indefinitely,  but  it  is  generally 
safer  to  embed  for  sectioning  without  great  delay;  this  is  especially 
true  of  tissue  which  has  been  fixed  with  Zenker's  solution.  Most  fixing 
fluids  also  harden;  the  terms  'fixing5  and  'hardening'  are  consequently 
often  used  synonymously. 


EMBEDDING 

Thick  sections  may  be  obtained  from  the  firmer  tissues  by  freehand 
sectioning  with  a  razor,  but  for  the  satisfactory  preparation  of  thin  sec- 
tions a  microtome  is  a  necessity  and  the  tissues  must  have  been  pre- 
viously embedded  to  render  them  sufficiently  firm.  This  is  accomplished 
by  infiltrating  the  tissue  with  celloidin  or  paraffin,  either  of  which  yields 
a  firm,  waxy  consistence. 

Embedding  in  Celloidin. — Make  a  saturated  solution  of  a  little  cel- 
loidin (Schering's)  in  a  mixture  of  equal  parts  of  alcohol  and  ether. 
The  alcohol  should  contain  no  trace  of  copper  sulphate.  This  solution 
is  for  convenience  known  as  number  III  and  should  have  a  very  thick, 
syrupy  consistence. 

A  small  portion  of  number  III  is  mixed  with  three  to  five  times  its 
volume  of  the  alcohol  and  ether  mixture,  to  obtain  number  II,  which 
should  have  a  somewhat  viscid  consistence. 

A  second  small  portion  of  number  III  is  diluted  with  ten  to  fifteen 
times  its  volume  of  the  alcohol  and  ether,  to  produce  celloidin  number 
I,  which  should  have  a  thin,  watery  consistence. 

Small  pieces  of  tissue  which  have  been  thoroughly  hardened  in  95 
per  cent,  alcohol  are  treated  as  follows: 

1.  Dehydrate  in  absolute  alcohol,  six  to  twenty-four  hours. 

2.  Place  in  the  absolute  alcohol  and  ether  mixture,  twelve  to  twenty- 
four  hours. 

3.  Place  in  celloidin  number  I,  twelve  to  twenty-four  hours. 

4.  Place  in  celloidin  number  II,  twelve  to  twenty-four  hours. 

5.  Place  in  celloidin  number  III,  twenty-four  to  forty-eight  hours, 
or  longer. 

Pieces  of  tissue  of  considerable  size  may  be  satisfactorily  embedded 


EMBEDDING  735 

in  celloidin,  but  should  be  passed  through  the  successive  solutions  in 
a  much  more  leisurely  manner.  Thus  an  eye  requires  two  to  three 
weeks,  a  large  piece  of  the  central  nervous  system  three  to  four  weeks 
for  proper  embedding.  The  tissue  should  now  be  fastened  to  a  wooden 
block  and  the  celloidin  hardened.  Ordinary  wood  yields  its  resins  to 
the  alcohol  in  which  the  blocks  are  to  be  kept ;  the  white  pine  blocks 
which  are  commercially  known  as  'deck  plugs'  contain  very  little  resin 
and  are  admirably  adapted  for  the  purpose.  Vulcanized  fiber  blocks  are 
still  better,  and  glass  blocks  are  also  serviceable.  The  piece  of  tissue 
should  be  so  oriented  upon  the  block  that  the  future  sections  may  be 
cut  nearly  parallel  to  the  block  surface.  Thick  celloidin  is  then  poured 
over  the  tissue;  a  few  moments'  exposure  to  the  air  cements  it  firmly 
to  the  block.  After  the  celloidin  has  become  firm  by  partial  drying  in 
air,  the  block  may  be  stored  indefinitely  in  70  per  cent,  alcohol  (stronger 
alcohol  is  apt  to  soften  the  celloidin),  where  the  hardening  is  completed. 
If  it  is  desired  to  harden  the  celloidin  rapidly  for  early  cutting,  the 
block  may  be  floated  in  a  jar  of  chloroform,  tissue  down,  for  two  or 
three  hours. 

The  final  step  in  the  embedding  process  may  be  accomplished  ad- 
vantageously by  allowing  the  tissue  to  remain  in  the  slowly  hardening 
thick  celloidin  in  a  shallow  dish.  Care  must  be  taken  to  begin  this 
step  with  sufficient  celloidin  to  keep  the  tissue  covered  until  the  harden- 
ing is  completed.  The  tissue  may  then  be  cut  from  the  firm  celloidin 
and  blocked. 

Embedding  in  Paraffin. — If  sections  thinner  than  15  p.  are  de- 
sired, paraffin  embedding  must  be  used;  it  is  impossible  to  cut  celloidin 
sections  with  any  great  degree  of  certainty  thinner  than  10  p  to  15  p., 
Paraffin  sections  are  readily  cut  at  5,  and  may  be  cut  as  thin  as  2  /x. 
The  paraffin  method  is  also  to  be  selected  for  the  rapid  preparation 
of  tissues  for  sectioning,  but  it  is  only  applicable  to  small  pieces  of 
tissue.  For  large  pieces  better  results  will  be  obtained  with  celloidin. 
Many  methods  for  the  employment  of  paraffin  have  been  extolled;  the 
following  can  be  recommended.  The  tissue,  after  fixation,  should  have 
been  hardened  in  alcohol. 

1.  Dehydrate  in  absolute  alcohol  twenty-four  to  forty-eight  hours; 
v^ery  small  pieces  of  tissue  (1  to  2  mm.)  may  be  completely  dehydrated 
in  three  to  six  hours. 

2.  Place  in  equal  parts  of  absolute  alcohol  and  xylol  (xylcne),  one 
to  three  hours. 

3.  Place  in  pure  xylol  until  clear  and  translucent,  one-half  to  two 


736  HISTOLOGIC  TECHNIG 

hours.     (For  relatively  large  pieces  of  tissue  cedar- wood  oil  or  pure 
anilin  oil  may  be  substituted  for  the  xylol). 

4.  Place  in  melted  paraffin  containing  a  little  xylol  (or  cedar  oil)  ; 
that  which  has  been  previously  used  for  embedding  does  very  well. 

5.  Transfer  to  pure  melted  paraffin. 

6.  Transfer  to  a  second  dish  of  pure  melted  paraffin  (with  melting 
point  of  about  54°).     The  object  of  these  changes  is  to  replace  the 
xylol   (or  oil)   with  pure  paraffin.     If  the  xylol  is  not  completely  re- 
moved the  tissue  will  contain  bubbles  and  satisfactory  sections  cannot 
be  made. 

7.  Embed  in  a  paper  box  or  a  watch  glass.     If  glass  is  used  the 
surface  should  be  smeared  with  the  least  trace  of  glycerin  to  prevent 
adhesion.    The  box  should  be  filled  with  pure  melted  paraffin,  the  tissue 
handled  with  warmed  forceps,  and  placed  with  proper  orientation  so 
that  it  is  completely  covered  with  the  melted  paraffin.     The  paraffin  is 
now  rapidly  cooled  by  immersion  in  cold  water;  in  summer  months 
ice  water  must  be  used.     If  a  paper  box  is  used  it  can  be  left  to  float 
on  the  water  until  the  paraffin  is  thoroughly  congealed.     The  manner 
of  preparing  these  boxes  is  shown  in  Fig.  594. 

Considerable  depends  upon  the  choice  of  a  proper  grade  of  paraffin. 
That  which  melts  at  58°  to  65°  is  most  desirable  for  use  in  temperate 
climates  during  the  warmer  months;  during  the  winter  months  paraffin 
of  54°  to  56°  is  preferable.  If  too  hard,  the  paraffin  cracks;  if  too  soft, 
it  fails  to  retain  its  form  during  sectioning.  The  former  condition  may 
be  improved,  if  necessary,  by  the  proximity  of  a  small  flame  during  the 
sectioning  process,  or  by  breathing  upon  the  loiif e  blade  and  tissue  block ; 
the  latter  fault  may  be  remedied  by  placing  the  tissue  for  a  short  time 
in  the  refrigerator,  just  prior  to  cutting. 


SECTIONING 

The  cutting  of  free-hand  sections  is  so  simple  an  operation  as  to 
scarcely  require  description.  A  small,  inexpensive  hand  microtome  and 
a  sharp  razor  whose  surfaces  are  ground  flat,  not  concave,  are  all  that  is 
necessary. 

For  more  precise  sectioning  a  stationary  microtome  is  a  necessity. 
Many  types  of  these  instruments  are  on  the  market.  The  Thoma  type 
of  instrument  is  specially  adapted  for  celloidin  work,  but  may  also  be 
used  for  paraffin  sections.  The  Schanze  instrument  is  very  useful  for 


SECTIONING 


737 


celloidin  sections  and  may  also  be  used  for  small  paraffin  sections.  The 
Minot  and  the  new  Spencer  rotary  microtomes  are  specially  adapted  for 
the  production  of  serial  sections  in  paraffin.  These  instruments  of  them- 
selves suggest  the  manner  in  which  they  are  to  be  used,  and  the  technic 
is  easily  acquired.  Like  all  delicate  instruments,  they  must  be  kept  well 
cleaned  and  properly  oiled,  to  do  good  service. 

Much  depends  upon  the  choice  and  care  of  the  knife.     The  micro- 
c  I  d 


a' 


D 


II 


FIG.  594. — A  METHOD  OF  PREPARING  A  PAPER  Box  FOR  PARAFFIN  EMBEDDING. 

7.  A  slip  of  paper,  A,  B,  D,  C,  is  folded,  both  ways,  on  the  lines  a-a',  5-6',  c-c', 
and  d-d'.  Then  being  folded  into  the  form  shown  in  //,  it  is  laid  flat,  the  section 
a,  a',  b',  b,  shown  in  7,  being  uppermost,  and  the  paper  is  creased  on  the  lines  e-e' 
and  /-/'.  It  is  then  opened,  folded  in  the  shape  of  a  box,  /,  e,  f,  e',  forming  the  bot- 
tom, and  is  secured  by  folding  down  the  ends  after  creasing  the  paper  on  the  lines 
e-f  and  f-e'. 

tome  knives  of  Jung  are  of  excellent  quality  and  should  be  kept  in  good 
condition  by  the  frequent  use  of  the  hone  and  strop. 

The  hone  should  be  of  fine  Belgian  stone.  It  should  be  well  moist- 
ened with  water,  the  addition  of  a  little  fine  soap  being  a  distinct  ad- 
vantage. The  edge  of  the  knife,  carefully  applied  to  the  hone,  should 
first  be  drawn  obliquely  from  heel  to  toe  and  toward  the  operator,  being 
held  at  a  constant  angle  and  drawn  the  whole  length  of  the  stone.  The 
knife  is  then  turned  over  and  the  motion  is  reversed,  the  knife  being 
held  obliquely  at  an  angle  equal  to  the  previous  one,  the  edge  directed 


738  HISTOLOGIC  TECHNIC 

away  from  the  operator,,  and  the  knife  pushed  from  heel  to  toe, 
the  whole  length  of  the  stone.  The  motion  being  repeated,  a  sharp 
edge  is  gradually  acquired,  which  can  be  finished  by  the  use  of  the 
strop. 

In  the  use  of  the  strop  the  motions  are  the  reverse  of  those  with 
the  hone,  the  back  of  the  knife  in  this  case  preceding  its  edge  as  it  is 
drawn  along  the  leather,  and  the  draw  should  be  from  the  toe  to  heel 
of  the  knife.  The  angle,  however.,  between  the  knife  and  the  hone  and 
the  knife  and  the  strop  should  always  be  a  constant  one,  and  should 
be  such  that  the  microscopical  'teeth'  which  are  thus  formed  on  the  edge 
of  the  knife  should  be  directed  obliquely  toward  its  heel. 

In  sectioning,  the  knife  should  be  so  placed  in  the  microtome  that 
its  edge  crosses  the  paraffin-embedded  object  at  right  angles,  and  for 
ribbon  sectioning  the  paraffin  block  should  be  so  trimmed  that  it  forms 
a  perfect  rectangle.  In  sectioning  celloidin-embedded  objects,  the  knife 
should  cross  the  object  at  as  acute  an  angle  as  possible.  With  paraffin, 
also,  the  stroke  should  be  sharp  and  quick;  with  celloidin,  somewhat 
slower  and  rhythmic.  The  knife  should  remain  dry  when  Used  with 
paraffin;  with  celloidin  both  the  knife  and  the  object  should  be  at  all 
times  well  moistened  with  70  per  cent,  alcohol. 


STAINING 

The  sections,  having  been  cut,  are  at  once  ready  for  staining,  pro- 
vided they  were  embedded  in  celloidin.  If  paraffin  was  used  for  em- 
bedding, the  sections  have  first  to  be  fastened  to  the  slide.  This  is 
accomplished  in  the  following  manner. 

The  paraffin  sections  are  properly  arranged  upon  the  surface  of  a 
clean  slide,  a  few  drops  of  water  from  a  pipette  are  allowed  to  flow 
between  the  slide  and  the  sections,  so  that  the  latter  float  upon  the 
surface  of  the  water;  and  the  slide  is  gently  heated  over  a  small  flame. 
Thus  the  paraffin  sections  are  straightened;  care  should  be  used  not 
to  melt  them.  The  excess  of  water  is  now  carefully  drained  off  and  the 
slide  placed  in  an  oven  and  heated  to  about  40°  C.  for  several  hours, 
until  thoroughly  dried.  Most  tissues  will  now  adhere  firmly  to  the 
slide.  If,  however,  the  tissue  was  fixed  with  solutions  containing  bi- 
chromate of  potassium  the  sections  are  liable  to  come  off  the  slide,  a 
misfortune  which  may  be  avoided  by  the  use  of  a  celloidin  adhesive, 
with  or  without  the  previous  use  of  Mayer's  albumin.  As  a  precautionary 


STAINING  739 

measure  against  the  loss  of  sections,  the  routine  use  of  albumin  ad- 
hesive is  recommended. 
Mayer's  Albumin: 

White  of  egg,  chopped  with   scalpel  or  scissors 

and   filtered 10  c.c. 

Glycerin    10  c.c. 

Thymol a  small  crystal 

A  drop  of  this  fluid  is  rubbed  evenly  upon  the  surface  of  a  clean 
slide.  Distilled  water  is  added  with  a  pipette  and  the  paraffin  sections 
arranged  upon  the  slide  by  the  method  detailed  above.  In  the  process 
of  drying  the  albumin  is  coagulated  and  the  tissue  becomes  firmly  at- 
tached to  the  slide.  The  drying  may  be  accomplished  without  special 
heating,  but  requires  at  least  twelve  hours  at  ordinary  room  tempera- 
tures. 

Celloidin  Adhesive. — The  sections  having  been  fastened  to  the  slide 
and  dried,  the  paraffin  is  removed  by  dipping  the  slide  into  one  or  two 
changes  of  pure  xjlol,  the  xylol  removed  by  washing  with  absolute  al- 
cohol, and  a  few  drops  of  very  thin  solution  of  celloidin  (made  by 
diluting  thin  celloidin,  number  I  (see  page  734)  with  eight  or  ten  vol- 
umes of  the  alcohol  and  ether  solvent)  are  poured  over  the  sections. 
The  solution  of  celloidin  should  be  so  thin  as  to  scarcely  leave  an  appreci- 
able film  on  the  slide.  The  excess  of  celloidin  is  drained  off  and  the 
film  hardened  by  first  flooding  the  slide  with  70  per  cent,  alcohol,  and 
after  a  few  minutes  transferring  it  to  water.  The  sections  will  not  now 
be  removed  from  the  slide  except  by  mechanical  violence.  In  handling 
serial  sections  of  embryos,  time  may  be  saved,  and  the  same  end  ac- 
complished, by  simply  spreading  by  means  of  a  soft  brush  a  thin  film 
of  the  very  thin  celloidin  solution  over  the  dried  paraffin  sections.  The 
sections  may  then  be  manipulated  for  staining  in  the  usual  way. 

Celloidin  sections  do  not  need  to  be  fastened  to  the  slide  before 
being  stained;  they  are  sufficiently  firm  to  be  gently  handled  with  a 
needle. 

Staining  in  Bulk. — It  is  occasionally  desirable  to  stain  tissue  in  bulk 
so  that  sections  once  cut  can  be  immediately  mounted.  This  is  best 
accomplished  by  the  use  of  a  single  stain  applied  to  small  blocks  of 
tissue  immediately  after  fixation  and  hardening,  and  is  usually  done  in 
aqueous  media.  Borax  carmin  is  the  most  useful  dye  for  the  purpose, 
and  is  used  as  described  below,  except  that  it  will  require  two  or  three 


740  HISTOLOGIC  TECHNIC 

days  to  penetrate  the  tissue.  Delafield's  hematoxylin  also  gives  brilliant 
results  in  bulk  staining. 

Regressive  Staining. — Staining  in  bulk  is  necessarily  a  regressive 
process,  viz.,  the  tissue  is  first  overstaiued  and  then  partially  decolorized. 
With  borax  carmin  the  decolorization  is  accomplished  by  acid  alcohol 
(hydrochloric  acid  1  c.c.,  70  per  cent,  alcohol  100  c.c.).  Since  the 
stain  is  removed  more  rapidly  from  the  cytoplasm  than  from  the  nucleus, 
a  differentiation  is  thus  produced. 

Progressive  Staining. — In  progressive  staining  the  dye,  having  been 
once  taken  up  by  the  tissue,  is  not  removed,  the  differentiation  of 
nucleus  and  cytoplasm  being  accomplished  by  the  selective  affinity  of 
the  dye.  Thus,  certain  dyes  are. nuclear  (basic),  others  are  cytoplasmic 
(acid).  The  former  possess  a  special  affinity  for  the  nucleus,  the  latter 
stain  both  nucleus  and  cytoplasm. 

Certain  dyes  may  be  used  either  progressively  or  regressively ;  in 
the  former  case  care  must  be  exercised  that  the  section  be  not  over- 
stained;  in  the  latter  case  overstating  is  impossible,  but  decolorizatiou 
must  be  watched  with  care. 

Classification  of  Dyes. — Dyes  may  be  classified  according  to  their 
affinity  for  certain  granules  or  other  portions  of  the  cytoplasmic  struc- 
ture. A  classification  of  this  kind  was  advanced  by  Ehrlich  through 
his  pupil,  G.  Schwartze  (Inaug.  Dissert.,  1880),  and  has  been  greatly 
elaborated  by  Pappenheim  (Grundriss  der  Farbechemie,  1901).  Such 
a  classification  is  very  incomplete  and  unsatisfactory,  but  in  a  very 
general  way  serves  a  useful  purpose.  The  following  is  sufficient  for  our 
present  needs: 

1.  Basic   dyes,   those   which   color   the   chromatin    of    the   nucleus 
(largely  nucleic  acid)   and  the  so-called  basophil  granules.     Hematein, 
methylene  blue,  methyl  green,  safranin,  and  basic  fuchsin  are  examples. 

2.  Acid  dyes,  those  which  are  usually  cytoplasmic  dyes,  and  have 
an  affinity  for  the  acidophil    (i.e.,  basic)    granules.     Such  are  eosin, 
Congo  red,  orange  G,  methyl  blue,  and  acid  fuchsin. 

3.  Neutral  dyes,  which  result  from  a  due  admixture  of  acid  and 
basic  colors,  and  which  gives  a  specific  tint  to  the  so-called  neutrophil 
or  azure  granules.     Such  dyes  are  Ehrlich's  triacid  mixture,  eosinated 
methylene  blue,  etc. 

4.  Specific  dyes,  which  result  from  the  due  admixture  of  dyes  with 
certain  reagents,  other  dyes  or  chemicals,  and  which  have  a  selective 
affinity  for  particular  tissues.    This  is  an  indefinite  class  which  includes 
Weigerf  s  elastic  tissue  stain,  Mallory's  connective  tissue  stain,  Sudan  III 


STAINING  741 

for  fat,  the  intra  vitam  staining  of  nerve  tissues  with  methylene  blue,  etc. 

Mordants. — The  successful  application  of  a  dye  requires  that  the 
tissue  shall  have  a  chemical  affinity  for  the  stain.  This  affinity  may  be 
either  natural  or  artificial,  e.g.,  eosin  will  color  nearly  all  tissues  under 
any  ordinary  conditions  without  the  aid  of  any  other  reagent;  the  colora- 
tion is,  however,  largely  a  physical  phenomenon,  due  to  inhibition 
of  the  dye;  hematoxylin,  on  the  other  hand,  stains  ordinary  tissue  but 
slightly,  but  its  action  is  much  enhanced  by  first  acting  upon  the  tissue 
with  alum  or  a  similar  reagent.  The  alum,  in  this  case,  serves  as  a 
mordant. 

A  mordant  should  have  a  strong  affinity  for  both  the  stain  and  the 
tissue.  Hence  it  is  that,  after  a  tissue  has  been  once  stained  by  the 
aid  of  a  mordant,  it  may  be  decolorized,  partially  or  completely,  by  the 
second  application  of  the  same  or  another  mordant  of  equal  strength. 


SINGLE  STAINS  WITH  NUCLEAR  DYES 

Hematein. — Hematein  is  the  active  principle  of  the  dye,  hema- 
toxylin, obtained  by  extracting  logwood.  Hematein  is  derived  from  the 
solutions  of  hematoxylin  by  oxidation,  either  by  chemical  reagents  or  by 
prolonged  exposure  to  the  air.  As  a  dye  it  must  be  combined  with  a 
mordant,  which,  most  frequently,  is  some  form  of  alum.  The  following 
formulas  are  recommended: 

Alum  Hematein  (Mayer)  : 

Alum  hematein   (Grubler's) 0.2  grm. 

95  per  cent,  alcohol 5      c.c. 

Saturated    aqueous    solution    of    ammonium 
alum 100     c.c. 

About  10  grm.  of  alum  are  required  for  this  solution.  The  hematein 
should  be  first  dissolved  in  the  alcohol,  with  gentle  heat  if  necessary, 
and  afterward  added  to  the  warm  solution  of  alum.  The  fluid  is  ready 
for  use  in  two  or  three  days,  but  will  increase  in  strength  for  several 
weeks;  it  then  requires  dilution. 

Bohmer's  Hematoxylin: 

Hematoxylin     0.5  grm. 

Absolute  alcohol 5      c.c. 

Saturated  aqueous  solution  of  potassium  alum  100      c.c. 


742  HISTOLOGIC  TECHNIC 

The  ingredients  should  be  mixed  as  above  and  allowed  to  stand  for 
eight  to  ten  days  in  an  open  bottle  and  exposed  to  sunlight.  Filter. 
Ripening  will  continue  for  some  weeks,  and  the  dye  will  require  dilution 
from  time  to  time  with  a  saturated  solution  of  potassium  alum. 

Delafield's  Hematoxylin : 

Hematoxylin    4  grm. 

95  per  cent,  alcohol 25  c.c. 

Saturated  aqueous  solution  of  ammonium  alum  400  c.c. 

Mix  as  above  and  permit  the  fluid  to  stand  in  an  open  vessel  ex- 
posed to  the  air  and  sunlight  for  three  or  four  days.  Add: 

Glycerin   100  c.c. 

Methylic  alcohol   100  c.c. 

Expose  to  light  in  a  cotton-plugged  bottle.  After  two  days  filter. 
After  several  days  filter  again,  and  keep  in  tightly  stoppered  bottle. 
The  fluid  will  ripen  for  several  weeks  and  may  require  dilution  with 
a  saturated  aqueous  solution  of  alum,  containing  glycerin  and  methylic 
alcohol  in  the  above  proportions. 

This  is  a  very  deep  nuclear  stain,  in  fact  it  is  so  deep,  that,  while 
the  nuclei  are  sharply  differentiated,  the  intranuclear  structure  is  nearly 
obliterated.  The  stain  is  somewhat  improved  in  this  particular  by  the 
slight  regressive  action  of  very  weak  acids — e.g.,  hydrochloric,  picric,  or 
dilute  acetic  acid.  This  is  a  very  useful  dye  for  the  toto  staining  of 
small  embryos. 

Mann's  Acid  Hematein  (Ehrlich's  Ilematoxylin]  : 

Hematein   (Griibler's)    or  hematoxyliii  crystals  2  grm. 

Absolute  alcohol   100  c.c. 

Glycerin   100  c.c. 

Distilled  water 100  c.c. 

Potassium  alum 10  grm. 

Glacial  acetic  acid 10  c.c. 

The  hematein  (or  hematoxylin)  is  dissolved  in  the  acetic  acid,  with 
25  c.c.  of  the  alcohol;  the  glycerin  and  the  remainder  of  the  alcohol 
are  then  added.  The  alum  is  dissolved  in  water  by  the  aid  of  heat, 
and  the  warm  solution  is  poured  slowly  while  stirring  into  the  solution 
of  hematein.  The  fluid  keeps  indefinitely  and  is  an  excellent  hematein 
stain  for  general  use.  Hematoxylin  solutions  may  be  ripened  immedi- 
ately by  the  addition  of  small  amounts  of  hydrogen  peroxide  (about  1 
c.c.  to  200  c.c.  of  stain,  neutralized  by  a  few  grains  of  sodium  chlorid). 


STAINING  743 

Application  of  the  Hematein  Stains.— All  of  the  above  solutions 
arc  used  in  a  similar  manner.  Sections,  either  free  or  attached  to  the 
slide,  are  taken  from  water  and  immersed  in  the  dye  for  three  to  five 
minutes;  they  are  then  thoroughly  washed  in  water.  The  stained  sec- 
tions are  at  first  of  a  reddish-purple  color,  but  soon  become  a  deep 
blue  from  the  slight  alkalinity  of  the  tap  water  used  for  washing.  If 
necessary  this  alkalinity  may  be  increased  by  the  addition  of  one  or  two 
drops  of  ammonia  to  500  c.c.  of  the  water  used  for  washing. 

Hematoxylin  solutions  require  air  and  sunlight  for  ripening.  After 
ripening  is  complete  the  solution  should  be  kept  tightly  stoppered.  The 
solutions  should  be  filtered  before  using.  Ehrlich's  hematoxylin  is  prob- 
ably the  best  nuclear  dye  for  general  routine  work.  Better  differentia- 
tion is  usually  obtained  if  the  sections  are  over-stained  (5  to  10  minutes) 
and  then,  after  thorough  washing,  partially  decolorized  in  a  1  per  cent, 
solution  of  hydrochloric  acid  in  70  per  cent,  alcohol  (a  few  seconds 
is  usually  sufficient),  washed,  and  the  color  restored  in  an  ammoniacal 
solution  (1  per  cent,  aqueous  solution  of  ammonium  hydroxid).  The 
sections  must  again  be  thoroughly  washed,  and  the  best  differentiation 
is  secured  if  the  sections  are  now  placed  in  very  dilute  watery  eosin  for 
ten  to  twelve  hours. 

Methylene  Blue. — This  dye  is  a  derivative  of  thionin,  and  may  be 
similarly  used.  For  staining  fresh  tissues  the  dye  is  used  in  2  per  cent, 
aqueous  solution.  Its  preparations  are  not  very  permanent.  The  chief 
uses  of  this  dye  are  in  combination  with  eosin  as  a  stain  for  blood;  as 
a  stain  for  nerve  cells  according  to  the  method  of  Nissl;  and  as  applied 
to  living  organs  as  a  specific  stain  for  nerve  tissues  after  the  method  of 
Ehrlieh.  These  methods  will  be  described  below. 

Methyl  Green. — This  dye  is  preferable  to  methylene  blue  as  a  stain 
for  fresh  tissues.  It  is  used  in  2  per  cent,  aqueous  solution  and  applied 
as  a  progressive  stain.  It  also  enters  into  the  composition  of  Ehrlich's 
triacid  mixture.  It  is  strongly  basic. 

Carmin. — This  valuable  dye  is  derived  from  the  cochineal  bug,  and 
is  used  either  as  a  progressive  or  a  regressive  stain.  For  the  former, 
picro-carmin  or  alum  carmin  are  recommended;  for  the  latter,  borax 
carmin  is  preferable. 

Borax  Carmin : 

Borax 4  grm. 

Distilled  water   (boiling) 100  c.c.;  cool,  filter,  and  add 

Carmin 3  grm. ;  when  dissolved,  add 

70  per  cent,  alcohol 100  c.c. 


'744  HISTOLOGIC  TECHNIC 

Mix  the  ingredients  in  the  above  order,  and  after  twenty-four  hours 
filter.  It  may  be  necessary  to  use  a  drop  or  two  of  ammonia  to  complete 
the  solution  of  the  carmin.  This  is  again  removed  by  evaporation. 

Tissues  are  to  be  overstained  in  the  carmin  solution,  and  differen- 
tiated in  acid  alcohol  (70  per  cent,  alcohol  containing  0.5  to  1  per  cent, 
of  hydrochloric  acid)  until  the  red  color  is  no  longer  removed  in  clouds. 
The  sections  are  then  well  washed  with  several  changes  of  95  per  cent, 
alcohol,  cleared  and  mounted.  This  is  a  most  excellent  dye  for  staining 
embryos  in  toto. 

Alum  Carmin: 

Potassium  alum   5  grm. 

Distilled  water    (hot) 100  c.c. 

Carmin 1  grm. 

Mix  in  the  order  given,  boil  for  twenty  minutes,  and  when  cold  filter. 
Picro-Carmin : 

Ammonium  hydrate 5  c.c. 

Distilled  water 50  c.c. 

Carmin 1  grm. ;  when  dissolved,  add 

Saturated    aqueous    solution    of 

picric  acid 50  c.c. 

Expose  to  light  and  air  for  two  days;  filter. 

*  Picro-carmin  is  used  as  a  progressive  stain.  Since  the  picric  acid  is 
soluble  in  alcohol,  dehydration  should  be  rapid,  or  a  crystal  of  picric 
acid  should  be  added  to  the  alchohol  used  for  dehydration. 

Aceto-Cannin. — This  is  an  invaluable  fluid  for  certain  purposes, 
especially  where  it  is  desired  to  study  nuclear  structure,  chromosomes 
and  spindles  in  fresh  and  uncut  (teased)  tissue.  The  tissue  is  simul- 
taneously fixed  and  stained  in  this  mixture,  and  remains  preserved  in  the 
fluid  in  a  condition  favorable  for  study  for  a  considerable  time.  The 
stained  tissue,  e.g.,  insect  testes,  etc.,  is  teased  out  on  a  slide  in  the  fluid, 
covered  with  cover  glass,  and  may  then  be  studied  under  an  oil  immer- 
sion lens.  The  mitotic  figures  are  almost  as  clear  as  in  sectioned  ma- 
terial. The  solution  is  made  by  dissolving  to  saturation  carmin  in  boil- 
ing acetic  acid  of  45  per  cent,  strength,  and  filtering. 

Safranin. — This  dye  is  a  coal-tar  derivative;  it  is  an  excellent 
nuclear  stain.  Like  carmin,  safranin  yields  a  deep  red  color. 

Safranin   0    (Griibler's) 1  grm. 

Distilled  water   .  .   100  c.c. 


STAINING  745 

1.  Tissues  taken  from  water  are  stained  five  minutes. 

2.  Wash  in  water. 

3.  Dehydrate  rapidly  in  absolute  alcohol.    The  afcohol  removes  some 
of  the  safranin,  giving  a  regressive  effect. 

I 

SINGLE  STAINS  WITH  CYTOPLASMIC  DYES 

Eosin. — This  dye  is  a  coal-tar  derivative.  There  are  no  less  than 
seventeen  varieties  of  the  dye  on  the  market,  of  which  five  are  in  general 
use.  These  are:  (1)  yellowish  alcoholic;  (2)  bluish  alcoholic;  (3) 
yellowish  watery;  (4)  bluish  watery;  (5)  pure  French  eosin.  The  most 
reliable  of  these  dyes  are  manufactured  by  Griibler.  The  first  and  fifth 
varieties  are  to  be  recommended  as  blood  stains,  the  first  and  fourth 
are  the  best  for  general  use.  Two  distinct  methods  are  based  upon 
this  choice  of  dyes. 

Method  I: 

Yellowish  alcoholic  eosin 1  grm. 

70  per  cent,  alcohol 100  c.c. 

This  stock  solution  is  usually  diluted  with  four  to  ten  volumes  of 
70  to  95  per  cent,  alcohol  just  before  using.  The  stain  is  preferably 
preceded  by  the  use  of  a  nuclear  dye,  after  which  the  sections  should 
be  dehydrated  in  95  per  cent,  alcohol. 

1.  Stain  in  the  diluted  eosin,  one  to  five  minutes,  or  until  the  sec- 
tions become  a  bright  red  color. 

2.  Wash  quickly  in  absolute  alcohol,  clear,  and  mount.     The  color 
is  dissolved  out  during  this  process,  producing  some  differentiation  by 
regression. 

Method  II: 

Bluish  watery  eosin 1  grm. 

Distilled  water   100  c.c. 

The  stock  solution  should  be  diluted  with  one  to  four  volumes  of 
distilled  water  before  using. 

1.  Tissues  are  taken  from  water  and  placed  in  the  dilute  eosin,  one 
to  five  minutes. 

2.  Wash  quickly  in  water  to  remove  the  excess  of  the  dye. 

3.  Pass  radially  through  graded  alcohol,  clear,  and  mount. 
Slight  differentiation  may  be  obtained  by  prolonging  the  washing 

in  water,  otherwise  the  stain  is  progressive.     Much  greater  differenti- 
4? 


746  HISTOLOGIC  TECHNIG 

ation  is  possible  with  either  eosin  method  by  making  the  stain  very 
dilute  and  staining  for  twenty-four  to  forty-eight  hours. 
Congo  Red : 

Congo  red   1  grm. 

Distilled  water 100  c.c. 

A  few  drops  of  dilute  acetic  acid  should  usually  be  added  to  the 
above;  the  bright  red  color  is  then  exchanged  for  a  dull  bluish  red,  and 
in  this  neutralized  condition  the  stain  usually  gives  the  highest  differen- 
tiation. The  dye  should  be  used  in  the  same  manner  as  watery  eosin 
(see  Method  II,  above).  Congo  red  gives  especially  good  results  when 
applied  to  fetal  and  young  tissues. 

Orange  G. — There  are  many  varieties  of  orange.  The  orange  Gr 
and  the  aurantia  of  Griibler  will  be  found  satisfactory.  As  a  cytoplasmic 
stain  the  former  is  preferable.  It  should  be  used  in  the  same  manner 
as  alcoholic  eosin  (see  Method  I,  above). 

Fuchsin. — Two  distinct  dyes,  the  one  of  acid,  the  other  of  basic, 
properties,  pass  under  this  name.  Acid  fuchsin  is  a  cytoplasmic  dye, 
but  when  used  in  acid  solution  has  a  slight  selective  affinity  for  the 
nuclei.  Basic  fuchsin  is  chiefly  useful  in  bacteriology.  It  is  also  used 
in  preparing  Weigert's  elastic  tissue  stain. 

It  is  recommended  that  euparal  be  used  as  a  mounting  medium 
with  this  group  of  stains.  The  tissue  may  be  mounted  directly  from  90 
per  cent,  alcohol. 

DOUBLE  STAINING 

Hematein  and  Eosin : 

1.  Stain  with  one  of  the  hem- 
atein  solutions,  preferably  Mann's 
or  Ehrlich's  for  general  use,  five 
minutes. 

2.  Wash  well  in  water. 

3.  Stain   in  watery  eosin,  one 

to    ten    minutes.      Or—  3.  Dehydrate   in    95   per  cent. 

alcohol. 

4.  Wash   quickly  in  water.  4.  Stain     in     alcoholic     eosin, 

one  to  five  minutes. 

5.  Dehydrate    in    absolute    al-  5.  Dehydrate   quickly    (one  to 
cohol.                                                         five  minutes)   in  absolute  alcohol. 

6.  Clear  and  mount.  6.  Clear  and  mount. 


STAINING  747 

Methyl  Blue  and  Safranin.  —  Methyl  blue  is  a  very  different  dye 
from  methylene  blue  but  is  practically  identical  Avith  water  blue  (Wasser 
blau).  It  is  an  acid  or  cytoplasmic  stain. 

1.  Stain  with  a  2  per  cent,  aqueous  solution  of  methyl  blue,  three 
minutes. 

2.  Einse  in  water. 

3.  Stain  in  a  1  per  cent,  aqueous  solution  of  safranin,  five  minutes. 

4.  Wash  in  water. 

5.  Differentiate  and  dehydrate  quickly  in  absolute  alcohol,  till  the 
sections  become   again  blue. 

6.  Clear   and  mount. 

This  method  gives  a  permanent  stain  which  yields  excellent  results 
with  certain  tissues — e.g.,  the  skin. 

Other  nuclear  and  cytoplasmic  dyes  may  be  combined  in  a  similar 
manner  to  the  above  methods. 

SPECIAL   STAINING   METHODS 

Iron  Hematoxylin    (Heidenhain)  : 
I.  Mordant: 

Ferric  alum  (iron  ammonium  sulphate — violet 

crystals)    2  grm. 

Distilled  water 100  c.c. 

II.  Stain: 

Hematoxylin     1  grm. 

95  per  cent,  alcohol 10  c.c. 

Distilled  water 100  c.c. 

1.  Mordant  the  sections  four  to  twelve  hours  in  I. 

2.  Rinse  in  water. 

3.  Stain  twelve  to  twenty  hours  in  II. 

4.  Wash  well  in  water.     The  sections  should  become  very  black; 
a  drop  or  two  of  ammonia  to  one-half  liter  of  water  often  improves 
the  color. 

5.  Decolorize  in  the  mordant,   watching  each   section  under  the 
microscope,  and  stopping  the  decolorization  at  the  proper  time  by — 

6.  Wash  thoroughly  in  slowly  running  water,  or  in  several  changes 
of  still  water. 

7.  Counter-stain  if  desired,  dehydrate,  clear,  and  mount. 


748  HISTOLOGIC  TECHNIC 

This  method  gives  an  excellent  stain  for  the  finer  nuclear  structure, 
mitosis,  etc. 

Muchematein   (Mayer)  : 

Hematein    (Griibler's) 0.2  grm. 

Glycerin    40  c.c. 

Aluminium  chlorid 0.1  grm. 

Distilled  water 60  c.c. 

Mix  the  ingredients  in  the  order  given,  rubbing  the  hematein  with 
the  glycerin  in  a  mortar.  One  or  two  drops  of  nitric  acid  added  to  the 
final  mixture  will  sharpen  its  properties  as  a  nuclear  stain. 

This  dye  is  used  as  a  specific  stain  for  mucinous  tissues.  It  is  used 
in  the  same  manner  as  hematein,  and  stains  rapidly  (three  to  ten 
minutes). 

Mucicannin    (Mayer)  : 

Carmin    1  grm. 

Aluminium  chlorid   0.5  grm. 

Distilled  water 2  c.c. 

50  per  cent,  alcohol 100  c.c. 

Mix  in  the  order  given ;  heat  over  a  small  flame  till  the  fluid  darkens 
(two  minutes) ;  after  twenty-four  hours,  filter.  For  use,  dilute  with 
five  to  ten  volumes  of  50  per  cent,  alcohol.  Like  muchematein,  mucicar- 
min  is  a  specific  stain  for  mucus-containing  cells.  It  also  stains 
rapidly. 

Weigert-Pal  Stain  for  Medullated  Nerve  Fibers.— The  tissues 
must  have  been  previously  fixed  in  Miiller's  fluid  or  in  10  per  cent, 
formalin,  washed  in  water,  hardened  in  alcohol,  and  sectioned. 

I.  Stain: 

Hematoxylin    1  grm. 

Absolute    alcohol    10  c.c. 

Distilled  water   90  c.c. 

Saturated  aqueous  solution  of  lithium  carbonate 

(1  to  80) 1  c.c. 

II.  Differentiating  Solution: 

Potassium  permanganate    0.25  grm. 

Distilled  water  .  100        c.c. 


STAINING  749 

III.  Decolorizing  Solution: 

1  per  cent,  aqueous  solution  of  oxalic  acid 50  c.c. 

1  per  cent,  aqueous  solution  of  potassium  sulphate  50  c.c. 

This  last  solution   should   be  freshly  prepared  by  mixing  the  two 
stock  solutions  just  prior  to  use. 

1.  Stain  sections   (six  to  twenty-four  hours)   until  black. 

2.  Wash  well  in  water.     A  few  drops  of  lithium  carbonate  solution 
added  to  the  water  may  improve  the  color,  which  should  become  a 
deep  blue-black. 

3.  Differentiate  until  the  gray  matter  becomes  brown   (one-quarter 
to  two  minutes). 

4.  Rinse  in  water. 

5.  Decolorize  until  the  white  matter  becomes  a  steel  blue,  the  gray 
matter    a   light   brown    (one-quarter   to    one   minute),    watching   each 
section   with   care. 

6.  Wash  thoroughly  in  several  changes  of  water,  or  in  running  water. 

7.  If  desired,  counter-stain  with  alum  carmin,  and  wash  in  water. 

8.  Dehydrate,  clear,  and  mount. 

Methylene  Blue,  for  non-medullated  nerve  fibers    (Intravitam 
Method) : 

I.  Stain : 

Methylene     blue     (Griibler's     frectif.     nach 

Ehrlich')     0.1  grm. 

Distilled  water  100      c.c. 

Dissolve  with  heat,  cool,  and  filter. 

II.  Fixing  Solution  (Bethe's)  : 

Ammonium  molybdate    1  grm. 

Distilled  water   20  c.c. 

Hydrochloric  acid,  C.  P 1  drop. 

The  solution  should  be  freshly  made  and  kept  at  or  near  0°  C. 

1.  The  method  is  only  applicable  to  living  tissues,  by  injecting  the 
blood-vessels  with  the  stain,  or  by  partially  immersing  in  the  staining 
fluid  small  pieces  of  tissue,  freshly  removed  from  the  living  animal. 

2.  After  ten  to  thirty  minutes,  rinse  in  normal  saline  solution,  and 
place  in  the  cold  fixing  solution  for  two  to  six  hours,  according  to  the 
size  of  the  pieces.     The  tissue  should  be  kept  cold. 

3.  Wash  well  in  distilled  water. 


750  HISTOLOGIC  TECHNIC 

4.  Dehydrate  quickly  in  95  per  cent,  and  absolute  alcohol,  kept  at 
or  near  0°   C. 

5.  Embed  in  paraffin.     At  a  convenient  time,  cut  and  mount. 
The  stain  is  rather  unstable,  but  may  be  kept  fairly  well  if  mounted 

in  glycerin  or  in  neutral  balsam. 

This  technic  is  invaluable  for  the  demonstration  of  the  terminal 
nerve  supply  of  tissues. 

Methylene  Blue,  for  chromophilic  (tigroid)  granules  in  cyton  and 
dendron  (Nissl's  Method): 

I.  Stain: 

Methylene  blue  (Griibler's  'B  pat/) 3.75  grm. 

Venetian  soap  (white  Castile) 1.75  grm. 

Distilled  water 1000        c.c. 

II.  Differentiating  Solution: 

Anilin  oil  (pure) 10  c.c. 

95  per  cent,  alcohol 90  c.c. 

This  method  is  only  applicable  to  tissue  which  has  been  fixed  in  95 
per  cent.,  or  in  absolute  alcohol.  Thionin  may  be  substituted  for  the 
methylene  blue  in  the  stain. 

1.  Warm   the  stain   till  steam  begins  to  rise ;  then   immerse   the 
sections  for  four  to  six  minutes.     They  acquire  a  deep  blue  color. 

2.  Rinse  in  distilled  water. 

3.  Differentiate  in  the  anilin  alcohol  till  the  sections  become  a  light 
blue,  carefully  observing  each  section    (twenty  to  sixty  seconds). 

4.  Wash  in  95  per  cent,  alcohol. 

5.  Clear  in  equal  parts  of  origanum  and  cajuput  oils,  and  mount 
in  neutral  balsam  or  in  colophonium  dissolved  in  xylol. 

Cajal's  Method  for  Demonstrating  Neurofibrils: 

1.  Fix  small  pieces  of  tissue  in  10  per  cent,  formalin  for  six  hours. 

2.  Wash  in  water  for  four  hours. 

3.  Transfer  to  40  per  cent,  alcohol  for  six  hours. 

4.  Place  in  50  c.c.  of  40  per  cent,  alcohol,  adding  5  drops  of  am- 
monia, for  twenty-four  hours. 

5.  Transfer  to  1.5  per  cent,  silver  nitrate  solution  at  incubator  tem- 
perature (38°  C.)  for  five  days. 

6.  Rinse,  and  place  in  a  solution  of  1  gram  pyrogallic  acid  or  hydro- 
chinon,  100  c.c.  water,  and  15  c.c.  formalin  for  twenty-four  hours. 

7.  Pass  through  graded  alcohols,  and  embed  in  paraffin  or  celloidin. 


STAINING  751 

For  other  more  complicated  Cajal  technics  for  demonstrating  neuro- 
fibrils,  also  for  the  Bielschowsky,  Bethe  and  Apathy  methods  for  the 
same  purpose,  reference  must  be  made  to  the  special  works  on  technic. 

Golgi  's  Stain  for  Nerve  Cells  (cyton,  axis  cylinder,  and  dendrons, 
and  neuroglia) : 

I.  Mordant  : 

'  1  per  cent,  aqueous  solution  of  osmium  tetroxid  10  c.c. 
3£  per  cent,  aqueous  solution'  of  potassium  bi- 
chromate      40  c.c. 

II.  Silver  Solution: 

Silver  nitrate    (crystals) 0.75  grm. 

Distilled   water    100        c.c. 

This  method  is  only  applicable  to  fresh  tissues,  and  the  best  results 
are  obtained  when  the  tissue  is  taken  from  a  fetus  or  from  an  animal 
not  over  three  days  old.  Thin  slices  or  small  fragments  of  tissue  must 
be  used. 

1.  Fix  in  the  mordant  for  ten  days,  frequently  changing  the  fluid, 
which  should  not  become  turbid,  nor  should  its  odor  of  osmium  tetroxid 
entirely  disappear. 

2.  Rinse  quickly  in  water. 

3.  Place  tissues  in  the  silver  solution,  diluted  with  two  volumes  of 
distilled  water,  for  fifteen  minutes. 

4.  Place    in    the    undiluted    silver    solution    twenty-four    to    forty- 
ciglit  hours.     If  several  pieces  of  tissue  are  prepared  they  should  be 
removed  at  intervals,  as  the  duration  of  the  impregnation  by  silver  is 
always  an  experiment. 

5.  Dehydrate  in  absolute  alcohol,  one  hour. 

6.  Transfer  to  equal  parts  of  absolute  alcohol  and  ether,  half  an 
hour. 

7.  Thin  celloidin  (number  1),  thirty  minutes. 

8.  Thick  celloidin  (number  3),  thirty  to  forty-five  minutes. 

9.  Transfer  to  a  wooden  block  and  fasten  with  celloidin. 

10.  Harden  the  celloidin  block  in  chloroform,  one-half  to  one  hour. 

11.  Cut  at  once,  the  sections  being  50  p.    to  100  /tt    thick.     While 
cutting,  the  knife  should  be  well  moistened  with  bergamot  oil,  not  al- 
cohol, and  the  sections,  if  not  mounted  at  once,  may  be  preserved  for 
a  short  time  in  the  same  oil.     Oil  of  lavender,  cajuput,  or  origanum 
may  be  used  in  a  similar  manner. 


752  HISTOLOGIC  TECHNIC 

Nitrate  of  Silver  for  Cement  Substances. — This  reagent  is  used 
to  outline  epithelial  cells  by  blackening  the  intercellular  substance,  the 
silver,  after  impregnation,  being  reduced  or  blackened  by  exposure  to 
light. 

1.  The  fresh  tissue  is  immersed  in  a  0.25  per  cent,  to  0.5  per  cent, 
aqueous  solution  of  silver  nitrate   (crystals),  and  left  in  the  dark  for 
ten  to  twenty  minutes.     Protargol  may  be  substituted  for  silver  nitrate 
crystals. 

2.  Wash  in  distilled  water,  and  while  still  in  water,  expose  to  direct 
sunlight  until  the  object  becomes  a  dark  reddish-brown  color   (ten  to 
thirty  minutes). 

3.  Transfer  to  70  per  cent,  alcohol,  three  to  twelve  hours. 

4.  Preserve  in  95  per  cent,  alcohol.     The  tissue  may  be  mounted  in 
the  usual  way. 

Since  nitrate  of  silver  will  attack  metal  instruments,  the  tissues 
while  in  this  solution  should  be  handled  with  glass  rods.  In  silvering 
serous  membranes,  it  is  well  to  slightly  stretch  the  object  by  tying  it 
over  a  cork  with  a  thread  tightly  fastened  around  the  edge. 

Gold  Chlorid  for  Nerve  Plexuses  and  Nerve  Endings  (Ranvier's 
Method).—!.  Wash  the  fresh  tissues  in  normal  saline  solution,  and 
place  them  in  pure  lemon- juice  until  they  appear  clear  (five  to  ten 
minutes) . 

2.  Wash  quickly  in  distilled  water. 

3.  Place  in  the  dark  in  a  1  per  cent,  aqueous  solution  of  chlorid 
of  gold  for  ten  to  forty-five  minutes,  according  to  the  permeability  of 
the  tissue. 

4.  Wash  in  distilled  water. 

5.  Place  in  a  25  per  cent,  aqueous  solution  of  formic  acid,  and 
keep  in  the  dark  for  twenty-four  to  forty-eight  hours. 

6.  Wash  thoroughly  in  water. 

7.  The  tissue  is  now  properly  teased  and  mounted  in  glycerin,  or 
sections  may  be  dehydrated,  cleared,  and  mounted  in  balsam. 

The  gold  method  is  used  for  the  demonstration  of  nerve  plex- 
uses and  nerve  terminations.  It  is  applicable  also  for  the  demonstra- 
tion of  certain  connective  tissue  cells,  e.g.,  corneal  cells,  and  tendon 
cells. 

Picro-Fuchsin  (Van  Gieson).— This  method  is  used  as  a  specific 
stain  for  connective  tissue;  it  colors  the  collagenous  fibers  a  bright  red, 
all  other  tissues  appearing  yellow.  Picric-acid-fuchsin  may  be  used 
as  an  after  stain  with  nuclear  dyes,  e.g.,  hematoxylin,  though  the  tissue 


STAINING  753 

must  be  greatly  overstained  with  the  nuclear  dye,  since  the  picric  acid 
will  decolorize  hematein. 

Saturated  aqueous   solution  of  picric   acid 100  c.c. 

1  per  cent,  aqueous  solution  of  acid  f uchsin ....       5  c.c. 

The  acid  fuchsin  solution  must  be  boiled  well  and  filtered  before 
adding  to  the  picric  acid  solution,  otherwise  a  precipitate  will  occur 
and  the  mixture  be  spoiled. 

1.  Stain  with  Delafield's  or  Bohmer's  hematoxylin,  fifteen  to  thirty 
minutes. 

2.  Wash  well  with  water.     The  sections   should  be  almost  black. 

3.  Stain  with  picro-fuchsin,  three  to  five  minutes. 

4.  Rinse  quickly  in  water   (water  removes  the  fuchsin).  . 

5.  Dehydrate  in  absolute  alcohol,  clear,  and  mount. 

Weigert's  Elastic  Tissue  Stain. — This  method  gives  a  specific  stain 
for  elastic  fibers;  it  may  be  used  alone,  or  in  combination  with  hema- 
tein and  picro-fuchsin. 

1  per  cent,  aqueous  solution  of  basic  fuchsin . .   100  c.c. 

2  per  cent,  aqueous  solution  of  resorcin 100  c.c. 

Boil  the  mixture  in  a  porcelain  dish,  and  while  hot,  add  liquor 
ferri  sesquichlorati  (Pharm.  Ger.,  Ill),  25  c.c. 

Heat  and  stir  for  five  minutes;  a  heavy  precipitate  is  formed.  Cool 
and  filter.  Dry  the  precipitate  in  a  porcelain  dish  over  a  water  bath 
or  sand  bath.  Dissolve  the  dried  precipitate  in  200  c.c.  of  95  per 
cent,  alcohol,  filter  and  replace  the  alcohol  lost  by  evaporation.  Add 
4  c.c.  of  pure  hydrochloric  acid. 

Tissues  should  be  stained  twenty  to  sixty  minutes,  then  thoroughly 
washed  in  water,  dehydrated,  cleared,  and  mounted. 

The  following  method  gives  very  beautiful  results: 

1.  Stain  in  Delafield's  or  Bohmer's  hematoxylin,  twenty  to  thirty 
minutes. 

2.  Wash  well  with  water. 

3.  Stain  in  Weigert's  elastic  tissue  stain,  twenty  minutes. 

4.  Wash  in  water. 

5.  Stain  in  picro-fuchsin,  three  to  five  minutes. 

6.  Rinse  quickly  in  water. 

7.  Dehydrate  in  absolute  alcohol,  clear,  and  mount. 

Orcein  may  also  be  employed  as  a  specific  stain  for  elastic  fibers. 
Mallory's  Connective  Tissue  Stain. — This    method    is    applicable 


754  HISTOLOGIC  TECHNIC 

only  to  tissues  which  have  been  fixed  in  Zenker's  solution  and  de- 
hydrated with  alcohol.  Somewhat  inferior  results  are  obtained  after 
fixation  with  mercuric  chlorid. 

It  stains  collagenous  fibers  and  reticulum,  blue;  nuclei,  neuroglia 
and  cytoplasm,   red;   and  hemoglobin    (red  blood  corpuscles),  yellow. 
Elastic  fibers  remain  unstained. 
I.  Stain: 

Acid  fuchsin 0.1  grm. 

Distilled  water    100      c.c. 

II.  Fixative: 

Phosphomolybdic   acid    1      grm. 

Dfstilled   water    100      c.c. 

III.  Counter-Stain: 

Anilin  blue    (soluble  in  water) 0.5  grni. 

Orange  G   (Griibler's) 2  grm. 

Oxalic   acid    . . 2  grm. 

Distilled  water  100  c.c. 

1.  Stain  in  the  fuchsin  solution,  three  to  twenty  minutes.     The 
sections  should  become  a  bright  red. 

2.  Wash  in  water. 

3.  Fix  in  the  phosphomolybdic  acid  solution,  one  minute.     This 
'fixes'  the  fuchsin  and  prevents  decolorizatiou. 

4.  Wash  well  in  water. 

5.  Counter-stain   in  the  anilin   blue  solution    (Xo.   Ill),  five  to 
twenty  minutes.    The  section  should  become  decidedly  blue. 

6.  Wash  in  watsr. 

7.  Dehydrate,  clear,  and  mount. 

Eosinate  of  Methylene  Blue  (Basting's  Method  for  Blood). — For 
the  somewhat  complicated  method  of  preparing  the  stain  the  reader  is  re- 
ferred to  the  original  article,  Johns  Hop.  Hosp.  Bull.,  1904,  vol.  xv,  p. 
122.  The  stain  is  applicable  to  smears  of  blood,  marrow,  splenic  cells, 
etc.  When  used  with  smears  which  contain  traces  of  fat,  a  preparatory 
treatment  with  a  2  per  cent,  aqueous  solution  of  sodium  metaphosphate, 
which  probably  serves  as  a  mordant,  improves  the  staining  properties, 
Otherwise  the  stain  is  applied  without  previous  fixation. 

1.  Stain  for  one  minute. 

2.  Dilute  the  stain  with  several  volumes  of  distilled  water,  and 


STAINING  755 

continue  the  stain  for  five  minutes,  or  until  satisfactorily  differentiated. 

3.  Wash  with  distilled  water. 

4.  Dry  and  mount. 

The  Giemsa  and  tlie  Wright  blood  stains  (other  modifications  of  the 
original  Romanowsky  stain)  may  be  used  for  the  same  purposes,  and 
are  applied  in  a  similar  manner. 

Eosin  and  Methyl  Blue  Mixture  (Mann) : 

1  per  cent,  aqueous  solution  of  methyl  blue 35  c.c. 

1  per  cent,  aqueous  solution  of  bluish  watery  eosin     45  c.c. 
Distilled  water    100  c.c. 

1.  Mordant  the  sections  in  water,  leaving  them  till  all  alcohol  has 
been  replaced  (five  to  thirty  minutes). 

2.  Stain  in  the  above  mixture,  five  to  ten  minutes. 

3.  Wash  well  and  differentiate  in  water;  the  effect  may  be  varied 
by  the  duration  of  the  washing   (ten  to  forty  minutes). 

4.  Dehydrate  in  alcohol,  clear,  and  mount. 

When  a  sharper  nuclear  dye  is  desired  the  stain  may  be  used  as  a 
counter-stain  after  hematein.  In  this  case  the  methyl  blue  solution 
should  be  allowed  to  act  only  three  to  five  minutes.  The  methyl  blue 
used  in  this  method  is  a  cytoplasmic  dye  and  should  not  be  confounded 
with  methylene  blue.  This  is  a  valuable  stain  for  differentiating  cyto- 
plasmic granules. 

Triacid  Stain  (Ehrlich) : 

Saturated  aqueous  solution  of  orange  G 13  c.c. 

Saturated  aqueous  solution  of  acid  f uchsin ....      7  c.c. 

Distilled  water   15  c.c. 

95  per  cent,  alcohol 15  c.c. 

Saturated  aqueous  solution  of  methyl  green.  . . .  12.5  c.c. 

95  per  cent,  alcohol 10  c.c. 

Glycerin    10  c.c. 

Be  certain  that  the  solutions  of  the  dyes  are  saturated,  and  mix  in 
the  order  given. 

The  following  formula  by  Mayer  may  be  substituted: 

Distilled  water   45  c.c. 

Glycerin 10  c.c. 

95  per  cent,  alcohol 25  c.c. 

Acid  fuchsin   3  grm. 


756  HISTOLOGIC  TECHNIC 

Orange  G 2  grm. 

Methyl  green  . . .  ^ 1  grm. 

Mix  the  fluids  and  dissolve  the  dyes  in  the  order  given. 
When  used  for  staining  sections,  either  of  these  formulas  should  be 
diluted  with  five  to  ten  volumes  of  the  following  mixture: 

Glycerin    10  c.c. 

Distilled  water   15  c.c. 

95  per  cent,  alcohol 25  c.c. 

1.  Stain  five  to  ten  minutes  in  the  diluted  solution.      (Use  full 
strength  for  blood  smears.) 

2.  Rinse  in  water. 

3.  Dehydrate  in  absolute  alcohol.     (Smears  are  dried  in  the  air.) 

4.  Clear  and  mount. 

The  best  results  are  obtained  with  tissues  fixed  in  a  sublimate  mix- 
ture. It  is  a  delicate  cytologic  stain,  and  is  serviceable  in  differentiating 
between  chromatin  (chromosomes)  and  plastin  (plasmosomes  and  linin)  ; 
also  in  differentiating  cytoplasmic  granules.  Sections  should  n»t  be  over 
3  /it  in  thickness.  The  stain  is  more  or  less  capricious. 

Auerbach's  Fuchsin-Methyl-Green  Stain.— This  stain  does  well 
only  after  a  sublimate  fixative.  It  is  serviceable  in  cytologic  work  for 
differentiating  between  'active'  and  'resting5  chromatin.  When  suc- 
cessfully manipulated  it  stains  the  chromosomes  green  and  the  plasmo- 
somes and  linin  red. 

Keep  in  separate  bottles  the  following  stock  solutions: 

I.  Acid  fuchsin  1  part,  distilled  water  1,000  parts. 
II.  Methyl  green  1  part,  distilled  water  1,000  parts. 

Mix  when  ready  to  use  in  the  following  proportions : 

2  parts  of  I,  acidulating  every  50  c.c.  with  1  drop  of  a  10  per 
cent,  solution  of  glacial  acetic  acid. 

3  or  4  parts  of  II. 

Fix  tissues  (e.g.,  insect  testes,  etc.)  in  the  sublimate  acetic  mixture, 
transfer  direct  to  80  per  cent,  alcohol  (removing  the  mercury  with  tinc- 
ture of  iodin),  dehydrate,  and  embed  in  paraffin.  Sections  should  not 
be  cut  over  3  p  thick. 

Stain  for  fifteen  minutes,  and  pass  directly  to  95  per  cent,  alcohol. 
When  the  green  stain  no  longer  leaves  the  sections  in  clouds,  pass 


STAINING  757 

rapidly  through  absolute  alcohol  and  xylol,  and  mount  in  balsam.  The 
sections  may  also  be  mounted  directly  from  95  per  cent,  alcohol  in 
euparal. 

Mitochondria!  Technics. — Mitochondria  (chondriosomes,  plasto- 
somes)  are  readily  destroyed  by  acids,  hence  these  must  be  eliminated 
from  fixing  solutions,  or  greatly  reduced. 

I.  MEVES'  METHOD. — This  is  the  simplest  method  for  demonstrating 
mitochondria,  and  in  many  instances  it  is  quite  satisfactory. 

Very  small  pieces  of  tissue  are  fixed  for  eight  days  in  Flemming's 
strong  solution  in  which  the  acetic  acid  has  been  reduced  to  3  or  4  drops 
in  the  simplest  formula  (see  page  728).  The  tissue  is  then  embedded 
in  paraffin  in  the  usual  way,  and  the  sections  cut  at  3  to  6 /n  are  stained 
by  the  iron-hematoxylin  method.  The  nuclei  and  cytoplasm  are  a  uni- 
form pale  gray;  the  mitochondria  appear  as  deep  black  granules,  rods 
or  filaments. 

II.  BENDA'S  METHOD. — This  is  a  more  complicated  technic,  but 
gives  excellent  results,  and  is  claimed  to  be  specific. 

1.  Fixation  in  strong  Flemming's  fluid  (acetic  acid  reduced  to 

3  drops)  for  eight  days. 

2.  Wash  in  water  one  hour. 

3.  Place  in  a  mixture  of  equal  parts  of  pyroligneous  acid  and  1 

per  cent,  chromic  acid  for  twenty-four  hours. 

4.  Transfer  to  a  2  per  cent,  solution  of  potassium  bichromate  for 

twenty-four  hours. 

5.  Wash,  dehydrate  and  embed  in  paraffin  and  fix  on  slide  in  the 

usual  way. 

6.  Mordant  sections  on  slide  in  4  per  cent,  solution  of  ferric 

alum  for  twenty-four  hours. 

7.  Rinse  with  water,  and  place  in  an  amber-yellow  aqueous  solu- 

tion of  Kahlbaum's  suphalizarinate  of  soda  (prepared  by 
dropping  1  c.c.  saturated  alcoholic  solution  in  100  c.c.  of 
water)  for  twenty-four  hours. 

8.  Einse  with  water,  flood  slides  with  a  solution  of  crystal  violet 

(1  vol.  sat.  sol.  of  dye  in  70  per  cent,  ale.;  1  vol.  1  per  cent. 
HC1  in  70  per  cent.  ale. ;  2  vols.  anilin  water)  and  warm 
until  vapor  is  given  off. 

9.  Rinse,  differentiate  one  or  two  minutes  in  30  per  cent,  acetic 

acid  solution. 
10.    Wash  in  running  water  five  to  ten  minutes. 


758  HISTOLOGIG  TECHNIC 

11.     Dry    with    blotting    paper,    drop    in    absolute    alcohol,    pass 
through  bergamot  oil  into  xylol  and  mount  in  balsam. 

According  to  Wildman  (Jour.  Morph.,  24,  3,  1913)  the  slides  may 
be  passed  from  the  alizarin  solution  after  rinsing,  1,  into  a  3  per  cent, 
solution  of  crystal  violet  (3  c.c.  anilin  stain  in  100  c.c.  distilled  water) 
for  ten  minutes;  2,  rinse  and  place  in  80  per  cent,  alcohol  for  five  sec- 
onds; 3,  pass  through  95  per  cent,  and  100  per  cent,  alcohol,  where  the 
differentiation  is  watched;  4,  clear  and  mount  in  the  usual  way. 

III.  EEGAUD'S  METHOD  (Arch.  d'Anat.  Micr.,  t.  11,  1910,  p.  296). 
— This  constitutes  a  very  satisfactory  routine  technic. 

1.  Fix  small  piece  of  tissue  for  twenty-four  hours  in  a  mixture  of 
Potassium  bichromate,  3  per  cent,  aqueous  solution. .   80  parts 
Formalin 20  parts 

2.  Transfer  to  a  3  per  cent,  aqueous  solution  of  potassium  bichro- 
mate.    This  acts  as  a  mordant.     The  tissue  should  be  left  in  this  solu- 
tion for  from  1  to  4  weeks,  with  several  changes  of  fluid. 

3.  Wash,  harden,  embed  in  paraffin,  and  cut  sections  of  from  3  to 
5  microns. 

4.  Stain  with  iron-hematoxylin. 

Mallory's  Phosphotungstic  Acid  Hematoxylin  for  Neuroglia  and 
may  be  used  to  advantage  with  the  connective  tissues)  (Jour.  Exp. 
Med.,  Vol.  19,  No.  5,  1900).— Tissues  should  be  fixed  in  Zenker's  fluid 
or  in  Kelly's  fluid.  It  stains  neuroglia,  myoglia  and  fibroglia  fibrils 
and  fibrin  and  nuclei  blue;  collagen  fibrils  are  stained  reddish-brown; 
other  intercellular  substances  pink. 

Hematoxylin 0.1  gram 

Water   80.0  c.c. 

Phosphotungstic   acid    (Merck),   10   per  cent. 

aqueous  solution 20.0  c.c. 

Dissolve  the  hematox3'lin  by  heating  in  a  small  amount  of  water; 
when  cool  add  to  rest  of  solution.  Allow  to  ripen  several  weeks.  The 
solution  can  be  ripened  for  immediate  use  by  addition  of  10  c.c.  of  14 
per  cent,  solution  of  potassium  permanganate,  or  by  the  addition  of 
0.2  gram  peroxid  of  hydrogen. 

1.  Pass  sections  through  graded  alcohols  to  water. 

2.  Place  in   14   per  cent,  aqueous  solution  of  potassium  perman- 
ganate for  five  to  ten  minutes. 


HISTOLOGIC  TECHNIC  759 

3.  Wash  in  water. 

4.  Place  in  a  5  per  cent,  aqueous  solution  of  oxalic  acid  for  five 
to  ten  minutes. 

5.  Wash  thoroughly  in  water. 

6.  Place  in  phosphotungstic  acid  hematoxylin  solution  for  twelve 
to  twenty-four  hours. 

7.  Dip  for  a  few  seconds  in  95  per  cent,  alcohol. 

8.  Clear  in  carbol-xylol  and  xylol  and  mount  in  xylol-damar. 

Vance's  Method  for  Staining  Bile  Canaliculi  (Anat.  Anz.,  Vol.  44, 
Xo.  17,  pp.  412-413). 

1.  Fix  tissues  in  Helly's  fluid ;  or  in  a  mixture  of  equal  parts  of 
10  per  cent,  formalin  and  5  per  cent,  mercuric  chlorid. 

2.  Embed  in  colloidia. 

3.  Place  sections  in  a  dilute  solution  of  iodin  in  95  per  cent,  alco- 
hol for  five  to  fifteen  minutes. 

4.  Remove  excess  iodin  by  washing  in  several  changes  of  95  per 
cent,  alcohol. 

5.  Stain  in  Mallory's  phosphotungstic  acid  hematoxylin  for  twenty- 
four  hours. 

6.  Transfer  directly  to  95  per  cent,  alcohol. 

7.  Clear  in  carbol-xylol  or  in  oil  of  origanum,  and  mount  in  balsam. 

Jenner's  Blood  Stain. — This  solution  acts  as  a  fixative  as  well  as  a 
stain.  Blood  smears  are  immersed  in  the  stain  for  two  to  five  minutes, 
washed  in  water,  dried  and  mounted  in  balsam. 

Water  soluble  eosin  (Griibler's),  1  per  cent,  aque- 
ous solution  : 100  c.c. 

Methylene  blue  (Griibler's),  1  per  cent,  aqueous 

solution  100  c.c. 

Mix  the  above  solutions;  after  twenty-four  hours,  filter.  Dry  the 
filtrate  at  65°  C.,  wash  the  dry  filtrate,  and  again  dry  and  powder.  Dis- 
solve 0.5  gram  of  the  powder  in  100  c.c.  pure  methyl  alcohol.  The 
result  constitutes  the  stock  solution. 

Zimmermann's  Technic,  for  demonstrating  the  intercalated  disks 
of  cardiac  muscle. 

1.  Small  piece?  of  tissue  are  fixed  for  twenty-four  hours  in  a  solu- 
tion of  90  parts  absolute  alcohol  and  10  parts  25  per  cent,  nitric  acid. 

2.  W;ish  in  several  changes  of  95  per  cent,  alcohol,  01  xintil  it  re- 
mains neutral  to  litmus  paper, 


760  HISTOLOGIC  TECHNIC 

3.  Pass  through  graded  alcohols  to  distilled  water. 

4.  Transfer  to  solution  of  1  gram  hemalum   (Griibler's)  to  10  c.c. 
water,  where  it  remains  for  eight  to  ten  days. 

5.  Wash  in  distilled  water,  embed  in  paraffin,  and  section. 

The  intercalated  disks  are  conspicuously  stained  a  dark  blue,  which 
contrasts  sharply  with  the  light-blue  background. 

These  disks  can  be  well  demonstrated  also  by  fixation  in  Carney's 
fluid,  followed  by  iron-hematoxylin  stain.  For  the  same  purpose  Heiden- 
hain  employs  vanadium  hematoxylin  after  sublimate  fixation  (see  Lee's 
Vade  Mecum). 

Gage's  Method,  for  Demonstrating  Glycogen.—  Glycogen granules 
are  readily  soluble  in  aqueous  media.  Tissue  which  is  to  be  tested  for 
this  substance  should  be  fixed  in  95  per  cent,  alcohol. 

1.  Embed  in  paraffin  in  the  usual  way. 

2.  Flatten  sections  on  slide  by  use  of  the  following  iodin  solution 

(Lugol's  solution),  which  is  subsequently  used  for  staining: 

Iodin 1.5  grm. 

Potassium  iodid 3.0  grm. 

Sodium  chlorid   1.5  grm. 

50  per  cent,  alcohol 300  c.c. 

3.  Stain,  dehydrate,  dissolve  paraffin. with  xylol,  mounted  in  melted 

vaselin,  and  seal  cover  glass  with  shellac.    The  glycogen  grains 
are  stained  mahogany  red. 

Osmic  Acid  Technic  for  Fat. — Free  fats  and  lipoids  are  soluble  in 
ether,  chloroform,  absolute  alcohol,  xylol,  benzene,  and  essential  oils. 
Since  these  must  be  employed  in  both  paraffin  and  celloidin  embedding, 
fat  cannot  be  very  satisfactorily  demonstrated  by  these  technics.  Frozen 
sections  (made  with  a  freezing  microtome)  of  fresh  or  formalin-fixed 
tissues  are  therefore  preferable  (in  some  instances  indispensable)  ;  these 
may  be  satisfactorily  stained  with  Sudan  III  (red),  Sharlach  E  (red), 
Nile  blue  (blue)  ;  they  must  be  mounted  in  glycerin  jelly. 

Osmic  acid,  however,  renders  certain  fats  resistant  to  solution  in 
oils,  and  tissue  so  fixed  may  accordingly  be  treated  by  the  paraffin  tech- 
nic;  but  thick  cedar  oil  must  be  substituted  for  xylol  or  chloroform,  and 
absolute  alcohol  should  be  avoided : 

1.  Fix  small  pieces  of  fatty  tissue  in  Flemming's  fluid  for  two  days. 

2.  (a)   Embed  in  paraffin  (use  cedar  oil),  section,  and  mount  in 

euparal;  or 


HISTOLOGIC  TECHNIC  761 

(b)  Embed  in  celloidin,  the  different  solutions  of  which  should 
be  made  up  in  95  per  cent,  alcohol  (see  Kingsbury,  Anat.  Rec., 
5,  6,  1911). 

Technic  for  Demonstrating  Chromaffin  Granules. — Chromaffin 
material  ('pheochrome'  granules;  adrenin  granules)  is  highly  susceptible 
to  solution  by  acids.  When  preserved  the  chrornaffin  granules  react  to 
chromium  (acid  and  solutions  of  salts)  and  stain  light  brown.  The 
best  method  for  their  preservation  is  Kelly's  fluid  (see  page  728),  which 
coincidently  stains  the  granules.  Paraffin  or  celloidin  sections  may  be 
stained  with  various  nuclear  dyes  for  the  clear  differentiation  of  the 
nuclei. 

Oelloidin-paraffin  Method  (Apathy;  Ztschr.  wiss.  Mikr.,  Bd. 
XXIX,  1912,  S.  449-515).— This  method  obviates  the  difficulties  en- 
countered in  sectioning  hard  and  brittle  objects,  e.g.,  chitin,  and  eggs 
with  yolk. 

1.  Place  thoroughly  dehydrated  tissues  in  ether-alcohol  for  at  least 
five  hours. 

2.  Thin  celloidin   (2  per  cent,  solution)  for  twenty-four  hours. 

3.  Thick  celloidin  (4  per  cent,  solution)  for  twenty-four  hours. 

4.  Pour  into  a  paper  embedding  box  or  a  glass  dish,  and  harden  in 
chloroform  vapor  for  twelve  hours. 

5.  Trim  the  block  quickly,  leaving  a  few  millimeters  of  celloidin  on 
each  side  of  object,  and  place  in  test  tube  of  chloroform  for  twelve 
hours. 

6.  Transfer  to  tube  of  following  oil  mixture  until  the  block  be- 
comes clear  and  sinks: 

Chloroform,  by  weight   4  parts 

Oil  of  origanum,  by  weight 2  parts 

Oil  of  cedar  wood,  by  weight 4  parts 

Absolute  alcohol,  by  weight .'....   1  part 

Carbolic  acid  crystals,  by  weight 1  part 

(Put  small  amount  of  dried  sodium  sulphate  into  bottom  of 

test  tube  to  take  up  the  water  brought  into  the  mixture  by  the 

celloidin.) 

7.  Wash  cleared  block  in  three  or  more  changes  of  benzol;  this  re- 
moves the  oils  and  alcohol,  and  prepares  for  paraffin  filtration. 

8.  Embed  in  paraffin,  section  and  mount  as  in  ordinary  paraffin 
technic.     (See  aho  Kornhauser,  Science,  July  14,  1916,  57-58.) 

48 


762  HISTOLOGIC     TECH  NIC 

MOUNTING 

After  staining,  the  sections  are  opaque;  they  must  be  rendered 
transparent  for  microscopic  examination.  This  is  accomplished  by  per- 
meating .the  sections  with  oil;  but  since  oil  and  water  are  net  miscible, 
the  tissue  must  first  be  thoroughly  dehydrated  with  alcohol.  Immers- 
ing thin  sections  in  95  per  cent,  alcohol  for  three  to  five  minutes  is 
usually  sufficient  for  this  purpose  .inless  xylol  is  to  be  used  as  the  clari- 
fying oil  or  unless  the  stain  is  injured  by  so  prolonged  au  immersion. 
In  either  of  these  cases  absolute  alcohol  is  ,to  be  used  for  dehydration, 
because  of  its  more  rapid  and  thorough  acfion. 

Clarification. — Sections,  either  free  or  fastened  to  the  slide,  are 
immersed  in  oil  until  clear.  Free  sections  ivill  at  first  float  on  the  oil, 
but  when  fully  permeated  will  sink.  Attached  sections  should  lose  all 
traces  of  'milky'  appearance.  The  following  oils  are  commonly  used  for 
clarification:  Bergamot,  origanum  cretici,  cajuput,  ciove,  carbol-xylol 
(pure  carbolic  acid,  melted,  25  to  33  c.c. ;  xylol,  75  to  6?  c.c.),  and  xyloi 
Xylol  (xylene)  is  the  most  desirable  in  that  it  is  perfectly  miscible 
with  the  balsam  in  which  the  section  is  usually  mounted,  and  is  finally 
lost  by  evaporation.  It  will  not  act  in  the  presence  of  the  least  trace  of 
water.  Carbol-xylol  has  the  advantage  of  a  slight  affinity  for  water; 
this  is  also  true  of  the  heavier  oils.  Complete  deh}rdration  is  therefore 
not  required.  Bergamot  is  desirable  for  celloidin  sections,  but  has  the 
disadvantage  of  rapid  deterioration,  after  which  it  dissolves  the  celloidin. 
Either  origanum  or  cajuput  oil,  or  a  mixture  of  the  two,  serves  well  for 
celloidin  sections,  but  leaves  them  somewhat  stiffer  than  does  bergamot 
oil.  The  latter  is  therefore  preferable  for  elastic  tissues.  On  the  whole, 
origanum  serves  best  for  routine  work  with  celloidin  sections,  xylol  or 
carbol-xylol  for  paraffin. 

After  clarification  celloidin  sections  must  be  transferred  to  a  slide. 
This  is  accomplished  by  means  of  a  metal  lifter  or  by  a  strip  of  rice 
paper  (ordinary  cigarette  paper  does  nicely).  The  section,  lying  on  the 
paper,  is  inverted  upon  the  surface  of  the  slide,  to  which  it  remains 
adherent  after  the  paper  is  gently  lifted.  The  excess  of  oil  is  then 
removed  with  blotting  paper  or  by  gentle  pressure  with  a  folded  towel, 
a  drop  of  xylol-balsam  applied,  and  the  cover  glass  dropped  into  position. 
The  preparation  is  permanent. 

Xylol-balsam  is  prepared  by  adding  to  Canada  balsam  sufficient 
xylol  so  that  the  mixture  will  have  a  thick,  syrupy  consistence,  but  will 
drop  from  a  glass  rod  without  stringing. 

Sections  may  also  be  permanently  mounted  in  glycerin  without  pre- 


MOUNTING  763 

vious  dehydration,  the  edge  of  the  cover  glass  being,  after  some  hours, 
covered  with  a  ring  of  King's  cement. 

Glycerin  jelly  is  also  serviceable,  and  does  not  require  cementing  of 
cover  glass. 

Neutral  Balsam. — Sections  may  frequently  be  rendered  more  per- 
manent by  the  use  of  neutral  balsam,  prepared  as  follows : 

Dilute  Canada  balsam  with  xylol  until  it  acquires  a  very  thin  watery 
consistence.  Add  sodium  bicarbonate  in  excess.  Shake  thoroughly,  and 
allow  to  stand  in  a  stoppered  bottle  for  twelve  hours  or  more.  Filter; 
this  is  readily,  though  slowly,  accomplished  if  the  dilution  is  sufficient. 
Permit  the  solution  to  stand  in  an  open  vessel,  protected  from,  dust, 
until  it  evaporates  to  the  proper  consistence  for  use. 

Gum-Damar. — This  material,  also  dissolved  in  xylol,  is  in  some  re- 
spects even  a  better  mounting  medium  than  balsam;  it  does  not  turn 
yellow  with  age. 

Euparal. — This  new  mounting  medium  is  for  most  purposes  the 
best.  Sections  are  mounted  direct  from  95  per  cent,  alcohol.  Delicate 
tissues  may  thus  be  spared  the  passage  through  absolute  alcohol  and 
oil.  This  curtailment  of  the  technic  is  also  a  saving  of  expense. 
Euparal  has,  moreover,  a  lower  index  of  refraction  than  balsam  or 
gum-damar,  and  is  thus  more  favorable  for  the  demonstration  of  cyto- 
logic  details  (see  Lee,  "Vade  Mecum,"  8th  ed.,  p.  247).  For  method  of 
preparation  see  Shepherd,  Trans.  Am.  Micr.  Soc.,  vol.  37,  p.  131,  1918. 

For  more  detailed  and  extensive  information  on  histologic  technic,  and 
microchemic  methods,  the  following  books  should  be  consulted: 

1.  Lee:  "The  Microscopist's  Vade  Mecum"  (8th  ed.,  1913).     Blakis- 

ton,  Phila. 

2.  Mann:  "Physiological  Histology."     Oxford,  1902. 

3.  Guyer:  "Animal  Micrology."     Univ.  of  Chicago  Press,  1906. 

4.  Hardesty:    "Neurological   Technique."     Univ.   of  Chicago  Press, 

1902. 

5.  Kingsbury:    "Laboratory    Directions   in   Histology  —  Histological 

Technique."     Ithaca,  N.  Y.,  1910. 

6.  Mallory  and  Wright:  "Pathological  Technique."     Saunders. 

7.  Enzyklopredie    der    mikroskopischen    Technik "    (2d    ed.,    1910). 

Urban  und  Schwarzenberg,  Berlin. 

8.  Gage:  "The  Microscope"  (llth  ed.,  1911).     Comstock  Pub.  Co., 

Ithaca,  N.  Y. 


DIRECTIONS  FOR  LABORATORY  WORK 

I.    INTRODUCTORY  EXERCISE 

This  exercise  is  designed  to  acquaint  the  student  with  the  diagnostic 
features  of  certain  more  common  laboratory  materials  which  may  become 
incorporated  with  bistologic  preparations;  and  to  serve  as  a  preliminary 
test  of  the  student's  facility  in  the  use  of  the  microscope  and  of  his 
acuity  of  observation. 

(1)  Mount  under  cover  glass  in  a  drop  of  water  a  human  hair,  a 
strand  of  wool,  and  a  few  rabbit  hairs.     Examine  with  the  low  power 
(l.p.)  of  the  microscope.     Sketch  (1)  a  short  segment  of  each  as  seen 
with  the  high  power  (h.p.). 

(Use  only  medium  hard  pencil.  Make  no  mark  that  does  not  cor- 
respond with  some  structural  feature  of  specimen  under  observation.) 

In  what  features  do  the  three  hairs  resemble  each  other? 

In  what  features  do  they  differ? 

Compare  surface  features  with  structure  of  axis  by  changing  the 
level  of  focus. 

(2)  Mount  on  separate  slides  in  water: 

(a)  a  few  cotton  fibers 

(b)  a  strand  of  silk 

(c)  some  finely  separated  threads  of  linen. 

Examine  with  l.p.  Note  differential  features.  Sketch  (2,  3,  4)  short 
segments  under  h.p. 

(Label  all  drawings.  Print  labels.  Use  broken  line  leaders,  ending 
with  arrow  at  point  or  structure  to  be  indicated.) 

(3)  Make  water  mount  of  a  small  mass  of  a  common  mould.    Notice 
the  long  branching  filaments  (hyphffi)  ;  and  the  spheroidal  spores,  from 
which  hypha?  may  occasionally  be  seen  sprouting.     Sketch  (5)  portion 
of  a  hypha.     Are  the  hyphae  segmented? 

(No  attempt  should  be  made  to  execute  a  drawing  of  a  preparation 
until  after  a  precise,  conception  has  been  acquired  of  the  structure  under 
examination  as  the  result  of  an  intelligent  study  with  both  the  low  and 
high  powers  of  the  microscope.) 

765 


766  DIKECTIONS  FOE  LABORATORY  WORK 


II.    THE  CELL 

(A)  THE  PLANT  CELL. 

(1)  Mount  in  water  a  small  piece  of  the  membrane  separating  the 
inner  layers  (leaves)  of  an  onion.    Note  shape  and  size  of  cells,  manner 
in  which  the  cells  are  grouped,  location  and  relative  size  of  nucleus, 
nucleoli,  cell  wall,  and  character  and  contents  of  the  cytoplasm.    Identify 
the  rod-shaped  mitochondria. 

Make  l.p.  sketch  (6)  of  a  small  group  of  cells;  and  h.p.  sketch  (7) 
of  a  single  cell.  Compare  with  section  of  cork.  Difference  ?  Propriety 
of  name  'cell'  ? 

(2)  Make  similar  preparation,  study  and  sketches  (8,  9)  of  a  thin 
slice  of  the  onion  leaf.    Identify  an  air  globule. 

(3)  Mount  in  water  a -thin  slice  of  the  potato.     Sketch  (10)  under 
h.p.  a  cell,  noting  carefully  the  nucleus  and  the  starch  grains.     Make 
careful  sketch  (11)  of  a  large  starch  grain.    Add  a  drop  of  tincture  of 
iodine,  and  note  the  color  change  of  the  starch  grains ;  and  observe  again 
the  shape,  size  and  location  of  the  nucleus. 

(4)  Examine  small  portion  of  the  leaf  of  a  common  higher  moss 
(e.g.,  Bryum),  and  sketch  h.p.  (12)  a  cell,  noting  especially  its  robust 
CELL  WALL,  and  its  content  of  chlorophyll  bodies  (chloroplasts). 

(B)  THE  ANIMAL  CELL. 

(1)  Scrape  gently  with  finger  inner  surface  of  cheek  and  mount  the 
debris.     Note  the  greatly  flattened  plate-like   cells    (squamous  cells). 
Make  l.p.  sketch  (13)  of  a  small  group;  h.p.  sketch  (14)  of  a  typical 
isolated  cell. 

(2)  OVUM  (egg  cell).    Make  a  careful  drawing  (15)   (from  demon- 
stration slide  of  starfish  ovary)  of  a  large  egg.     Note  endoplasm,  exo- 
plasm,  cell  membrane,  and  nuclear  membrane.     In  the  cytoplasm  ob- 
serve spongioplasm,  hyaloplasm,  microsomes;  in  the  nucleus,  chromatin, 
nucleolus,  linin,  chromioles,  and  karyosomes.     Character  of  cytoplasm? 

\3)  Sketch  (16,  a)  cell  with  mitochondria  (demonstration  slide); 
(16,  b)  cell  with  ergastoplasmic  fibrils  (e.g.,  acinar  cell  of  pancreas,  or 
lining  entodermal  cell  of  yolk-sac  of  10  mm.  pig  embryo). 

(4)  Sketch  (17)  astral  system  (demonstration  slide  of  maturing 
or  segmenting  egg  of  some  invertebrate,  e.g.,  starfish,  clam).  Note  cen- 
trosome,  centriole,  centrosphere,  astrosphere,  and  achromatic  spindle. 


DIRECTIONS  FOE  LABORATORY  WORK  767 

(5)  Sketch  (18)  section  of  full  grown  ovum  of  blood-starfish  (Hen- 
ricia  sanguineolenta)  ;  noting  especially  the  multinucleolated  condition 
of  the  nucleus,  and  the  graimlo-alveolar  character  of  the  cytoplasm.    The 
eggs  of  many  amphibians  during  later  growth  stages  also  have  a  multi- 
nucleolated nucleus. 

Sketch  (19)  a  small  area  of  this  cytoplasm  demonstrated  with  an  oil 
immersion  lens. 

(6)  LIVING  PROTOPLASM.    Mount  a  drop  of  a  hay  infusion  culture 
of  amebae  and  paramecia. 

Examine  first  a  paramecium.  Observe  ciliary  movement.  When  the 
protozoon  comes  to  rest,  note  exoplasm,  endoplasm,  metaplasm,  nuclei 
(macronucleus  and  micronucleus),  contractile  vacuoles  and  the  finely 
granulo-alveolar  character  of  the  cytoplasm.  Sketch  (20).  Observe  the 
cytoplasmic  changes  occurring  during  the  death  of  the  animal. 

In  an  ameba,  observe  manner  of  progression  (ameboid  movement), 
the  nucleus,  food  vacuoles,  water  and  contractile  vacuoles;  and  note  the 
homogeneous  or  very  finely  granular  character  of  the  protoplasm.  Sketch 
(21).  Observe  the  protoplasmic  changes  during  death. 

(Unless  otherwise  specified  all  drawings  are  in  future  to  be  made 
with  the  high  power  of  the  microscope.) 

III.    CELL  DIVISION 

(A)  AMITOSIS  (Akaryokinesis,  Direct  division).      , 

(1)  Sketch  (22)  several  stages  in  the  amitotic  division  of  the  nu- 
cleus (from  demonstration  preparation,  e.g.,  ductuli  efferentes  of  epi- 
didymis  of  mouse;  mesenchyma  of  young  embryo — 10  da.  turtle  em- 
bryo).    Study  direct  division  or  'budding*  of  yeast  cells. 

(2)  Sketch  (23)  a  multinucleated  ('giant')  cell  from  the  yolk  sac 
of  a  10  to  15  mm.  pig  embryo  (demonstration  preparation).    These  cells 
arise  from  mononucleated  cells  through  amitotic  division  of  the  nucleus. 

(B)  MITOSIS  (Karyokinesis,  Indirect  division). 

(I)  Sketch  (2\)  successive  steps  in  the  mitotic  division  of  cells  from 
the  root  tip  of  some  vigorously  growing  young  plant  (e.g.,  dog-tooth 
violet,  onion,  hyacinth,  spiderwort  (tradescantia),  etc.): 

(a)  cell  with  nucleus  in  the  resting  condition. 

(b)  nucleus  with  close  spireme. 

(c)  with  loose  spireme. 


708  DIRECTIONS  FOR  LABORATORY  WORK 

(d)  segmented  spireme  (Prophase  stages). 

(e)  chromosomes  in  equatorial  plate   (monaster  figure);  Meta- 
phase  stage. 

(f)  some  stage  of  the  migration  of  the  daughter  chromosomes 
(derived  from  a  longitudinal  splitting  of  the  prophase  mother 
chromosomes)  towards  the  poles  (Anaphase).     (The  double 
group  of  chromosomes  of  the  anaphase  stage  is  designated 
the  disaster  figure.)      (The  achromatic  spindle  holding  the 
chromosomes  is  called  the  amphiaster.) 

(g,  h,  i)  three  stages  in  the  reconstitution  of  the  nuclei  of  the 
two  daughter  cells  (Telophase) ;  these  are  the  same  as  the 
prophase  stages,  but  follow  in  inverse  order.  Note  presence 
of  mid-body  or  cell-plate  at  anaphase. 

How  do  the  two  daughter  cells  resulting  from  a  division  differ  in 

shape,  and  in  the  disposition  of  their  major  axis,  from  the  mother  cell? 

Note  changes  in  nuclear  membrane ;  formation  of  achromatic  spindle 

(centrosomes  are  lacking  in  flowering  plants) ;   different  position  of 

chromosomes  on  spindle  at  metaphase  and  anaphase. 

(2)  Make  a  similar  series  of  drawings  (25)  of  stages  of  mitosis  in 
the  epithelial  cells  from  sections  of  the  skin  of  the  tail  of  an  amphibian 
larva  (e.g.,  salamander,  frog).  (Demonstration  slide.) 

IV.    HISTOGENESIS 

(1)  Sketch  (26)  several  phases  in  the  segmentation  of  the  egg  of 
the  starfish,  including  the  two  and  four  cell  (blastomere)  stages. 

(2)  Sketch  (27)  a  transverse  section  of  a  vertebrate  embryo  (e.g., 
frog  or  salamander  larva),  showing  an  early  stage  in  the  formation  of 
the  germ  layers.    Label  ectoderm,  mesoderm,  entoderm,  notochord,  neu- 
ral groove  (canal),  somite,  celom,  and  the  primitive  intestine. 

V.    EPITHELIUM 

I.    Simple  (Non-stratified). 

(A)  POLYHEDRAL  (e.g.,  column  of  liver  cells). 

The  polyhedral  represents  the  least  modified  type  of  cell,  from  the 
standpoint  of  shape.  The  original  or  embryonic  shape  of  all  cells  is 
spheroidal.  All  the  morphologic  types  of  cells  may  be  interpreted  in 
terms  of  a  mechanically  modified  spheroidal  cell. 


DIRECTIONS  FOR  LABORATORY  WORK  763 

(1)  Sketch  (28)  a  few  isolated  cells  from  a  dissociated  (macerated) 
preparation  of  the  liver.     Note  the  number  and  position  of  the  nuclei, 
general  shape  of  the  cell,  character  of  cytoplasm,  cytoplasmic  granules 
(glycogen)   and  droplets  (fat),  and  cell  membrane  (?).     (Dissociated 
tissues  are  best  preserved  for  study  in  a  solution  of  equal  parts  of  abso- 
lute alcohol,  glycerin  and  water). 

To  a  teased  fresh  preparation  of  liver  in  physiologic  salt  solution  add 
a  drop  of  a  5  per  cent,  aqueous  solution  of  acetic  acid.  This  will  cause 
the  nucleus  to  appear  more  distinctly.  It  dissolves  also  all  albuminous 
granules,  but  leaves  unaltered  fat  and  lipoids.  (This  method  of  treat- 
ment may  be  profitably  employed  with  all  fresh  dissociated  (teased) 
preparations.  In  the  case  of  the  connective  tissues,  the  acetic  acid  will 
cause  the  collagen  fibers  to  swell  and  finally  disintegrate,  but  will  have 
no  effect  upon  the  elastic  fibers.) 

Subsequently  add  to  the  same  preparation  a  drop  of  a  1  per  cent, 
solution  of  methylene  blue.  This  will  stain  the  nucleus  and  thus  cause 
it  to  contrast  more  sharply  with  the  cytoplasm.  (Other  equally  good 
staining  solutions  for  isolated  tissues  are:  (a)  a  1  per  cent,  solution  of 
methyl  green  in  20  per  cent,  alcohol;  (b)  1  per  cent,  aqueous  solution 
of  borax  carmin;  (c)  dilute  solution  of  any  of  the  hematoxylin  stains; 
(d)  or  a  1  per  cent,  a'queous  solution  of  eosin  may  be  employed  to  stain 
the  cytoplasm,  producing  in  this  way  also  a  heightened  contrast  between 
nucleus  and  cytoplasm.) 

(The  best  way  to  add  any  fluid  to  a  macerated  preparation  under  a 
cover-glass  is  to  place  a  few  drops  of  the  solution  at  one  edge  of  the 
cover-glass,  and  cause  it  to  flow  under  the  glass  by  withdrawing  fluid 
from  the  opposite  edge  by  means  of  blotting  paper.)  Distinguish  be- 
tween physical  and  chemical  coloration. 

(2)  Sketch  (29)  a  small  area  of  a  stained  section  of  the  liver. 

(B)  SQUAMOUS  (Pavement  epithelium). 

(1)  MESOTIIELIUM.    Sketch  (30)  small  area  of  toto  mount  of  piece 
of  mesentery   of  cat,  treated   with   silver   nitrate   solution   to  outline 
the  intercellular  cement  and  lightly  stained  with  Dtlafield's  hematoxy- 
lin.   Note  the  character  of  the  cell  borders,  shape  of  cell,  position  and 
shape  of  nucleus,  stomata  (?),  guard  cells  (?),  and  stigmata.     Study 
a  stainod  section  of  the  amnion. 

(2)  ENDOTIIELIUM.     Sketch  (31)  small  area  of  lining  of  capillary 
or  small   vein    (e.g.,  from  toto  mount  of  mesentery,  or  pia  mater  of 
brain).     Note  sinuous  <-li;inirlor  of  cell  outline.     What  is  the  relation  of 


770  DIRECTIONS  FOR  LABORATORY  WORK 

the  long  axis  of  the  endothelial  cell  to  the  long  axis  of  the  blood  vessel? 
How  does  it  differ  in  shape  from  the  mesothelial  cell?  Sketch  (32)  also 
a  few  endothelial  cells  (profile  view)  from  a  stained  section  of  a  small 
blood  vessel. 

(3)  MESENCHYMAL  EPITHELIUM  (ranges  from  the  cubic  to  the  squa- 
mous  type  of  cell).     Sketch  (33)  a  group  of  the  epithelial  cells  from  a 
stained  section  of  the  synovial  membrane.     (This  is  more  generally  of 
the  cubic  type  of  epithelium.)      Note  membrana  propria  and  tunica 
propria. 

(4)  Sketch  (34)  a  few  of  the  squamous  cells  (flattened  entodermal 
cell&)  lining  the  pulmonary  alveoli,  from  a  stained  section  of  the  lung; 
also  (35)  a  small  area  of  the  superficial  cells  of  the  skin  or  of  the  mucosa 
of  the  esophagus. 

(C)  COLUMNAR. 

(a)  Plain. 

(1)  Sketch   (36)   a  few  isolated  columnar  cells  from  a  macerated 
preparation  of  the  mucosa  of  the  stomach,  or  of  the  small  intestine. 
Note  striated  border,  and  position  of  nucleus. 

(2)  Sketch  (37  a)  a  small  area  of  the  epithelium  from  a  stained  sec- 
tion of  the  stomach  or  small  intestine.    Note  proximal  (basal,  attached) 
and  distal  (free)  ends  of  cell,  striated  border  and  terminal  bars.    Note 
terminal  bars  in  those  portions  of  the  sections  where  the  columnar  epithe- 
lium is  cut  in  a  tangential  plane  near  the  distal  border.    Sketch  (37,  b). 

(b)  Modified. 

(1)  Goblet  cell.     Sketch  (38)   several  isolated  goblet  cells  from  a 
macerated  preparation  of  colon. 

(2)  Sketch  (39)  small  area  of  epithelial  lining  of  colon,  from  stained 
section.    Functional  tenure  of  a  goblet  cell? 

(3)  Pyramidal  (glandular)  cell.     Sketch  (40)  a  transverse  section 
of  fundus  of  a  tubular  or  tubo-acinar  gland   (e.g.,  gastric,  salivary), 
showing  the  pyramidal  shape  of  the  glandular  epithelial  cell  of  the 
secretory  fundus  or  acinus.    Note  the  lumen  of  the  gland,  and  the  char- 
acter of  the  cytoplasm  at  the  distal  and  proximal  poles  of  the  cells. 

(4)  Ciliated  cell.     Sketch   (41)   several  isolated  ciliated  cells  from 
a  macerated  preparation  of  the  trachea.     (These  columnar  ciliated  cells 
formed  part  of  a  pseudostratified  columnar  ciliated  epithelium.     See 
below.) 

(5)  Sketch  (42)  a  portion  of  the  epithelium  of  the  uterus  or  ovi- 
duct, from  a  stained  section. 


DIRECTIONS  FOR  LABORATORY  WORK  771 

(6)  Study  in  physiologic  salt  solution  ciliated  cells  scraped  from 
the  roof  of  the  mouth  of  a  pithed  frog.    Observe  the  activity  of  the  long 
cilia.      (An  equally  instructive  preparation  can  be  obtained  from  the 
gills  of  a  living  oyster  or  clam.)     Sketch  (43). 

(7)  Pigmented  cell.     Sketch    (44)    a  few  pigmented  cells   (cubic) 
from  the  pigment  layer  of  the  retina  or  the  iris,  from  a  stained  section 
of  the  eye. 

(8)  Flagellate  cell.     Sketch   (45)   a  spermatozoon  from  a  stained 
section  of  a  mammalian  testis;  or  from  a  preserved  specimen  of  human 
semen. 

(9)  Neuroepithelium.     Sketch   (46)  a  few  cells  from  the  bacillary 
(rod  and  cone  cell)  layer  of  the  retina,  in  a  stained  section  of  the  eye. 

(D)   CUBIC. 

Sketch  (47)  a  small  extent  of  cubic  epithelium  in  the  loop  of  the 
uriniferous  tubule,  from  a  stained  section  of  the  kidney. 

II.  Complex  (Stratified]  Epithelium. 

(1)  Squamous.    Sketch  (48)  portion  of  the  mucosa  of  the  esophagus, 
from  a  stained  section.     (A  stained  section  of  cornea  or  of  thin  skin  is 
almost  equally  favorable.)     Note  the  intercellular  bridges  between  cells 
of  the  middle  layers,  especially  prominent  in  skin. 

(2)  Sketch  (49)  the  several  types  of  cells  included  in  a  stratified 
squamous  epithelium,  from  a  macerated  preparation  of  the  esophageal 
mucosa. 

(3)  Pseudostratified  columnar.     (This  type  is  almost  invariably  cil- 
iated— exceptions,  larger  ducts  of  glands,  portion  of  ductus  deferens.) 
Sketch   (50)   small  extent  of  mucosa  of  trachea  or  bronchus,  from  a 
stained  section.     (This  type  of  epithelium  is  sometimes  erroneously  re- 
ferred to  as  'stratified  columnar'.     True  stratified  columnar  epithelium 
is  of  meagre  and  variable  occurrence,  sometimes  as  patches  among  the 
pseudostratified  epithelium.     Stratified  columnar  epithelium  occurs  in 
the  mucosa  of  the  intermediate  portion  of  the  male  urethra.) 

(4)  Transitional.     Study  carefully  and  draw  (51)  a  small  area  of 
the  lining  epithelium  of  the  bladder  or  ureter  (preferably  in  the  slightly 
distended  condition)   from  a  stained  section. 

(5)  Sketch  (52)  the  several  characteristic  types  of  cells  which  con- 
stitute a  transitional  epithelium  from  a  dissociated  preparation  of  the 
bladder  mucosa. 


772  DIRECTIONS  FOB  LABORATORY  WORK 

VI.    CONNECTIVE  TISSUE 

(A)  FIBEOUS  VARIETIES  (or  connective  tissue  proper).    These  de- 
velop from  the  middle  germ  layer  (mesoderm). 

(1)  EMBRYONAL.    Study  the  subcutaneous  tissue  in  a  stained  trans- 
verse section  of  a   10  to   20  mm.  pig  embryo.     Note  differences   in 
appearance  of  deeper  and  more  superficial  regions,  representing  earlier 
and  later  stages  in  the  histogenesis.    Draw  (53  a  and  b)  small  area  from 
each  of  the  two  regions.    Note  the  shape  of  the  cells,  and  the  character 
and  quantity  of  the  intercellular  substance.     Is  embryonic  connective 
tissue  (mesenchyma)  composed  of  discrete  cells  or  does  it  correspond  to 
a  syncytium?    Does  the  matrix  contain  fibrils? 

(2)  Mucous   (Gelatinous).     This  type  is  found  typically  only  in 
the  umbilical  cord,  where  it  is  known  as  the  jelly  of  Wharton.     The 
vitreous  humor  of  the  eye  is  also  comparable  to  mucous  connective  tissue. 
In  a  stained  section  of  the  umbilical  cord  study  a  region,  some  distance 
removed  from  the  large  central  blood  vessels,  and  note  the  various  forms 
of  cells;  and  the  character  and  quantity  of  the  intercellular  substance 
(matrix),  including  the  fibrils.     Draw  (54)   a  small  area.     Is  mucous 
connective  tissue  syncytial  in  character?     Is  it  vascularized ?     Define 
'fibroglia.' 

(3)  RETICULAR    (Retiform).     This   forms   the   supporting  frame- 
work for  the  cells  (lymphocytes)  in  lymphoid  tissue.     Select  for  study 
a  thinner  region  of  stained  section  of  some  lymphatic  organ  (e.g.,  hemal 
node,  lymph  node,  spleen)   where  the  lymphocytes  are  sparse.     Draw 
(55)  a  small  area,  noting  the  character  of  the  fibril  bundles,  and  their 
relation  to  the  lymphocytes  and  to  certain  stellate  connective  tissue  cells. 
Do  the  bundles  anastomose?     (A  demonstration  preparation  of  the  retic- 
ulum  of  a  lymph  node  or  of  the  spleen,  from  which  the  lymphocytes  have 
been  removed  by  'digestion',  or  by  shaking,  or  by  washing  in  warm  water 
after  gelatin  injection  and  freezing — Mall's  technic — may  be  substituted 
to  advantage  for  this  exercise.) 

(4)  AREOLAR  (Loose  fibro-elastic).     This  type  includes  fibro-elastic 
structures   of   greatly   varying   densities.      Spread   out   taut   on    slide 
a  thin  film  of  fresh  subcutaneous  or  intermuscular  tissue  of  some  mam- 
mal (e.g.,  guinea  pig,  rabbit,  rat).     Allow  the  ends  to  dry  fast  to  the 
slide,  keeping  the  center  moist  with  physiologic  salt  solution.     Mount 
under  cover-glass  and  examine  the  several  types  of  fibers.    Note  the  dull, 
white,  wavy  bundles  of  collagen  fibrils,  and  the  clear,  shiny,  stouter  elas- 


DIRECTIONS  FOR  LABORATORY  WORK  773 

tic  fibrils.  The  latter  may  be  arranged  in  a  wide-meshed  network. 
Sketch  (56)  a  bundle  of  white  fibers.  Do  the  bundles  anastomose? 
Sketch  (57)  also  several  elastic  fibers.  Do  they  branch?  Explain  the 
curled  character  of  some  of  the  fibers.  Add  several  drops  of  a  5  per  cent, 
aqueous  solution  of  acetic  acid.  Note  that  the  collagen  fibrils  swell, 
some  of  the  bundles  become  beaded,  and  finally  disintegrate.  What  is 
the  significance  of  the  beaded  condition  of  the  bundles  of  collagen  fibrils? 
Note  difference  in  structural  and  chemical  characteristics  of  the  collagen 
(white)  and  elastic  (yellow)  fibers.  Add  a  drop  of  a  nuclear  dye  (e.g., 
methylene  blue  solution)  and  examine  and  sketch  (58)  the  several  types 
of  cells:  (a)  spindle-shaped  cell;  (b)  plasma  cell;  (c)  lamellar  cell; 
(d)  clasmatocy te ;  (e)  granular  leukocyte.  Wash  the  preparation  in  dis- 
tilled water  and  add  several  drops  of  a  1  per  cent,  solution  of  magenta 
(basic  fuchsin)  in  70  per  cent,  alcohol.  This  will  stain  the  elastic  fibers 
(red).  Examine  the  preparation  for  final  study  of  the  elastic  fibers. 

Sketch  (59)  a  small  area  of  subcutaneous  tissue  from  a  section  of 
skin  stained  with  Weigert's  elastic  tissue  stain  (resorcin-fuchsin),  Dela- 
field's  hematoxylin  and  Van  Gieson's  stain  (picric-acid-fuchsin).  Note 
cells,  fibers  and  intercellular  spaces  ('tissue  spaces',  filled  with  'tissue 
fluid'). 

(5)  DENSE  WHITE  FIBROUS  TISSUE   (e.g.,  tendon,  sclera  of  eye). 
Study  a  longitudinal  section  of  tendon.     Sketch    (60)    a  small  area 
under  the  l.p.  noting  the  fasciculi.    Sketch  (61)  h.p.  a  small  area  from 
a  transverse  section  of  tendon.     Note  shape  of  cells  and  nuclei,  their 
arrangement  with  respect  to  each  other  and  the  bundles  (fasciculi)  of 
white  fibrils.    Tease  a  fragment  of  tendon  (from  tail  of  rat  or  leg  muscle 
of  rabbit)  in  salt  solution ;  add  a  few  drops  of  a  5  per  cent,  aqueous  solu- 
tion of  acetic  acid  to  destroy  some  of  the  collagen  fibrils;  add  a  few 
drops  of  methylene  blue  solution;  sketch  (62)  several  isolated  cells.     (A 
stained  macerated  preparation  of  tendon  is  an  equally  favorable  material 
for  study  of  tendon  cells.) 

(6)  DENSE  ELASTIC  TISSUE.     Study  a  teased  or  macerated  prepa- 
ration  of  ligamentum  nucha3  of  ox,  and  make   drawing    (63)    of    a 
few  fibers.    Note  transverse  markings  in  portions  of  some  fibers.    Sketch 
(64)  small  areas  of  stained  (Van  Gieson's  dye)  sections,  (a)  transverse 
and  (b)   longitudinal,  of  ligamentum  nuchae. 

(B)  MODIFIED. 

(1)  ADIPOSE  (Fat}  TISSUE.  This  is  modified  areolar  tissue.  Study 
a  cover-glass  mount  of  fresh  fat,  from  the  subcutaneous  tissue  of 


774  BISECTIONS  FOB  LABOEATORY  WORK 

a  mammal  (e.g.,  mouse,  rabbit).  As  the  fat  cools  note  the  formation  of 
margaris  crystals.  Add  a  drop  of  methylene  blue  and  sketch  (65)  several 
cells.  Note  shape  and  size  of  cell,  position  of  nucleus,  and  character  of 
cytoplasm.  Sketch  (66)  several  cells  from  a  teased  specimen  of  fresh 
fat  preserved  in  osmic  acid.  What  is  the  color  of  the  fat  globule?  Add 
eosin  stain  and  note  cytoplasm,  fat  globule  and  nucleus.  Sketch  (67) 
small  area  of  fat  in  subcutaneous  tissue  from  stained  section  of  skin  or 
capsule  of  some  gland,  e.g.,  pancreas,  kidney.  Note  position  of  nucleus, 
and  distribution  of  cytoplasm.  What  effect  has  alcohol  and  ether  pres- 
ervation on  fat?  Distinguish  between  nuclei  of  connective  tissue  and 
fat  cells. 

Sketch  (68)  developing  adipose  tissue  from  stained  section  of  sub- 
cutaneous tissue  of  young  animal.  (Developmental  stages  are  commonly 
to  be  found  also  in  the  areolar  tissue  enveloping  the  pancreas,  kidney 
and  other  viscera.) 

(2)  LYMPHOID    (Adenoid)    TISSUE.      (Modified    reticular   tissue.) 
Study  a  stained  section  of  a  small  lymph  node.    Note  cortex  and  medulla. 
Sketch  (69)  small  area  of  medulla,  including  the  denser  tissue  of  the 
medullary  cords  and  the  enveloping  looser  tissue  of  the  sinuses.    In  the 
sinuses  the  reticular  tissue  is  especially  prominent. 

(3)  PIGMENTED   CONNECTIVE   TISSUE.      (Modified  areolar  tissue.) 
Study  section  of  derma   and   subcutaneous   tissue   of   negro    skin ;   or 
the  choroid  coat  (middle  tunic)  of  the  eye;  (or  toto  mount  of  skin  of 
young  salamander  or  lizard).    Sketch  (70)  several  pigment  cells.    Note 
various  irregular  shapes  of  cells,  and  form  and  distribution  of  the  pig- 
ment granules  (melanin  granules).    Does  the  nucleus  contain  pigment? 
What  is  the  distinction  between  a  'pigment  cell'  and  a  'pigmented  cell'? 

(4)  NOTOCHOEDAL  TISSUE.     This  is  of  entodermal  origin    (ecto- 
dermal    in    the   guinea    pig;    G.    Carl    Huber),    and    resembles    con- 
nective tissue  only  in  its  grosser  features.    It  is  represented  in  the  adult 
only  in  the  nuclei  pulposi  of  the  intervertebral  discs.     Sketch    (71) 
small  section  of  notochord  from  stained  transverse  section  of  a  10  to  20 
mm.  pig  embryo. 

(5)  NEUROGLIA.     This  is  the  connective  tissue  of  the  central  nerv- 
ous system   (brain  and  spinal  cord).     It  is  of  ectodermal  origin.     It 
will  be  considered  in  connection  with  nervous  tissues. 

(C)  SUSTENTATIVE. 

(a)   Cartilage  (Gristle). 

(1)   HYALINE.     Make  l.p.  study  of  cartilage  plate  and  enveloping 


DIRECTIONS  FOR  LABORATORY  WORK  775 

perichondrium  (articular,  costal,  tracheal  or  bronchial).  Sketch  (72) 
narrow  segment  of  entire  plate.  Make  h.p.  drawing  (73)  of  (a)  peri- 
chondrium and  (b)  central  portion  of  plate.  Note  carefully  transition 
from  perichondrium  to  cartilage ;  cell  groups,  lacuna,  capsule  and  hyaline 
matrix.  Are  blood  vessels,  lymph  vessels  or  nerves  discernible  in  the 
matrix?  The  fetal  precursor  of  the  majority  of  bones  is  also  hyaline 
cartilage.  What  is  the  fundamental  structure  of  the  hyaline  matrix  ? 

(2)  ELASTIC    CARTILAGE     (Yellow    fibro-cartilage).      Study    car- 
tilage plate  of  the  epiglottis  or  the  external  ear   (e.g.,  ox)   in  stained 
section.     Note  elastic  fibers  in  the  hyaline  matrix.     (Some  specific  elas- 
tic tissue  stain  should  have  been  employed  with  the  section.)     Sketch 
(74)  a  segment  from  perichondrium  to  center  inclusive. 

(3)  FIBRO-CARTILAGE    (White   fibro-cartilage).      Study    a    stained 
section    of    an    intervertebral  disc    (e.g.,    ox)    or    the    semilunar    car- 
tilage of  the  knee.     Is  a  perichondrium  present?     Note  the  collagen 
fibers  in  the  matrix  (a  specific  collagen  fiber  stain  should  be  employed, 
e.g.,  Mallory's  or  Van  Gieson's).     How  does  fibro-cartilage  differ  from 
hyaline  cartilage  and  from  tendon?    Sketch  (75)  a  small  area  of  central 
portion  of  cartilage  disc.     Structural  differences  between  intervertebral 
disc  and  semilunar  cartilage  of  knee? 

(4)  PRECARTILAGE.     Sketch    (76)    a  small  area  of  the  condensed 
mesenchyma  in  the  region  of  a  future  bone  in  a  transverse  stained  sec- 
tion of  some  mammalian  embryo,  e.g.,  pig  of  10  to  15  mm. 

(5)  VESICULAR  SUPPORTING  TISSUE.     A  variety  of  connective  tis- 
sue   found    in    the    sesamoid    bone    of    the    tendon    of    Achilles    of 
the  f-rog,  characterized  by  abundant  large  clear  cells  scattered  among 
bundles  of  collagen  fibrils,  is  somewhat  similar  to  mammalian  fibro-carti- 
lage, and  represents  a  transition  from  dense  connective  tissues  to  carti- 
lage.    Study  a  section  of  the  tendon  of  Achilles  of  the  frog.     Note  dif- 
ferences and  similarities  between  this  tissue  and  mammalian  tendon  and 
fibro-cartilage.    Sketch  small  area. 

(b)  Pone  (Osseous  tissue). 

(1)  GROSS  STUDY.     Study  macroscopically  and  with  hand  lens  a 
longitudinally  cut  long  bone  (e.g.,  femur).    Note:  central  marrow  cav- 
ity, peripheral  compact  bone  of  diaphysis,  and  terminal  cancellous  bone 
of  epiphyses.    Note  also  jagged  border  of  marrow  cavity  terminally. 

(2)  MACERATED  COMPACT  BONE  (ground  section  of  bone).     Study 
l.p.  a  transverse  section  through  the  diaphysis.     Note:   central  mar- 
row cavity,  outer  circumferential   (periostcal)    lamellae;  inner  circum- 
ferential  (endosteal)   lamellae;  interstitial  lamellae;  Haversian  systems 


77G  BISECTIONS  FOR  LABORATORY  WORK 

(canal  and  lamellae) ;  lacunae,  and  canaliculi.  Sketch  (77)  a  complete 
Haversian  system.  What  are  the  contents  of  the  Haversian  canal? 
What  is  the  structure  of  the  osseous  lamellae?  Content  of  lacunae?  Sig- 
nificance of  canaliculi?  Study  a  fragment  of  a  ground  longitudinal 
section  of  the  shaft  (diaphysis)  of  a  long  bone.  Sketch  (78)  a  Haver- 
sian canal  at  the  point  of  branching,  with  the  enveloping  lamellae.  Note : 
Volkman's  canals  of  the  circumferential  and  interstitial  lamellae.  Are 
the  latter  connected  with  the  Haversian  systems?  Do  the  Haversian 
systems  connect  with  the  periphery  and  the  central  marrow  cavity? 
What  are  the  nutrient  foramina  of  a  bone?  How  many  to  the  shaft  of 
a  long  bone?  to  an  epiphysis? 

(3)  DECALCIFIED    COMPACT    BONE.      Study    stained    longitudinal 
section   of   end   of   long  bone   including   epiphysis   and   part  of    dia- 
physis.     Note:    periosteum,    muscle    attachments,    fibers    of    Sharpey, 
Haversian  systems,  bone  cells,  endosteum,  marrow.    Sketch  (79)  typical 
areas  from  epiphysis  (cancellous  bone)  and  diaphysis  (compact  bone), 
and  periosteum. 

(4)  BONE  DEVELOPMENT. 

(a)  ENCHONDRAL  OSSIFICATION  (Substitution  Bone).    Study  a  lon- 
gitudinal stained  section  of  a  decalcified  small  fetal  long  bone  (e.g.,  pha- 
lanx of  finger,  or  metacarpal ;  or  some  small  bone  of  fetal  pig) .    Sketch 
(80)  l.p.  a  narrow  strip  of  section  through  center  of  ossification  and  in- 
cluding terminal  articular  cartilage  and  central  marrow  cavity.     This 
drawing  should  illustrate  the  successive  stages  in  the  process  of  enchond- 
ral  ossification.     Sketch   (81)  h.p.  a  strip  through  area  of  ossification. 
Note:  calcified  cartilage  remnants  and  adjacent  rows  of  disintegrating 
cartilage  cells ;  primary  marrow  spaces ;  periosteal  bone ;  spicules  of  pri- 
mary bone;  and  epiphyseal  line  of  cartilage?   Sketch  (82)  :  (a)  perios- 
teum; (b)  strip  of  periosteal  bone,  including  a  periosteal  bud  of  osteo- 
genic  tissue  within  a  Haversian  space  (the  precursor  of  a  Haversian  sys- 
tem) ;  (c)  plate  of  enchondral  bone  with  central  calcified  cartilage  core 
and  surface  layer  of  primordial  bone,  bone  cells,  bone  lacunas,  and  peri- 
pheral osteoblasts  and  asteoclast  (in  a  Howship's  lacuna)  ;  (d)  primor- 
dinal  marrow  areola  with  marrow  cells,  including  blood  cells,  osteoblasts 
and  giant  cells  (megakaryocytes  and  polykayocytes — osteoclasts). 

(b)  INTRAMEMBRANEOUS   OSSIFICATION.     Study  stained  section  of 
jaw  of  some  mammalian  fetus  (e.g.,  of  pig  fetus  of  about  35  mm.)  for 
developing  membrane  bone    (cancellous  bone).      Sketch    (83  a)    small 
area  of  core  of  plate.     Sketch    (83  b)   an  osteoclast,  noting  the  con- 
tent of  resorbed  bone  globules. 


BISECTIONS  FOB  LABORATORY  WORK  777 

VII.    MUSCULAR  TISSUE 

(A)  SMOOTH  (Unstriped,  Plain,  Non-striated,  Involuntary  Smooth). 

(1)  Sketch  (.84)  several  isolated  cells  from  a  macerated  preparation 
of  smooth  muscle  from  the  wall  of  the  bladder,  stomach  or  intestines  of 
the  cat,  or  from  a  teased  .fresh  preparation  of  bladder  of  frog.     Note 
shape  of  cell,  position  of  nucleus,  fibrillar  and  granular  content  of  cyto- 
plasm,  pcrinuclear   coarsely  granular  sarcoplasm,  and  cell  membrane 
(sarcolemma). 

(2)  Study  smooth  muscle  in  a  stained  section  of  the  stomach  or 
intestines.     Make  l.p.  sketch   (85)   of  area  including  fibers  cut  trans- 
versely and  longitudinally.     Sketch  (86)  h.p.  a  small  area  of  cross-cut 
fibers.     Note  variations  in  shape  of  cross  sections  and  the  position  of 
the  nucleus.    Why  do  not  all  of  the  cross  sections  of  the  fibers  contain 
a  nucleus?     Sketch   (87)   h.p.  small  area  of  longitudinally  cut  fibers. 
Note  the  manner  in  which  the  fibers  are  joined  into  membranes.    Why 
do  many  of  these  cells  appear  much  shorter  than  the  isolated  cells? 
Study  wall  of  one  of  the  blood  vessels  of  the  umbilical  cord.    Sketch  (88) 
a  few  cells.     Is  an  intercellular  cement  present?  intercellular  bridges? 
Study  also  smooth  muscle  of  bladder,  and  of  a  pregnant  uterus.    Where 
in  the  body  are  the  longest  smooth  muscle  cells  found  ?    Study  the  nerve 
supply  of  the  smooth  muscle  of  the  intestine  in  a  demonstration  prep- 
aration. 

(B)  CARDIAC  (Involuntary  striped). 

(1)  Sketch  (89)  a  fragment  of  the  cardiac  syncytium  (myocardium) 
from  a  macerated  preparation  of  the  heart ;  or  from  a  teased  fresh  speci- 
men.    Note  the  branching  of  the  muscle  trabecula?,  position  of  nuclei, 
fibrils,  sarcoplasm,  cross  striations,  and  sarcolemma. 

(2)  Make  sketch  (90)  of  small  area  of  a  stained  section  including 
both  transversely  and  longitudinally  cut  trabecula?  ('fibers').    Note  posi- 
tion of  the  nucleus,  myofibrils,  cross  striations  (ground  membranes,  Z 
lines,  or  telophragmata)  and  intercalated  discs.     What  is  the  relation- 
ship between  the  telophragmata  and  the  sarcolemma?  between  the  telo- 
phragmata and  the  nuclear  membrane?     Are  other  striations  present 
besides  the  Z-stripes? 

(3)  Sketch  (91)  small  area  of  a  specially  prepared  demonstration 
slide  (Zimmermann's  techuic)  to  show  the  several  types  of  intercalated 
discs.     Tease  in  glycerin  a  fragment  from  a  hemalum-stained  block  of 
myocardium.    Determine  the  complete  form  of  the  intercalated  discs. 


778  DIRECTIONS  FOE  LABORATORY  WORK 

(4)  Sketch  (92)  portion  of  developing  myocardium  from  a  stained 
transverse  section  of  some  mammalian  embryo  (e.g.,  pig  embryo  of  from 
10  to  20  mm.  length).  Note  the  shape,  and  the  myofibrillar  cytoplasmic 
content,  of  the  constituent  myoblasts.  Do  the  myoblasts  anastomose? 
Is  heart  muscle  originally  syncytial  in  character? 

(C)     STRIPED  (Striated;  Voluntary  striped}. 

(1)  Tease  a  fragment  of  fresh  frog's  or  other  vertebrate's  muscle  in 
normal  salt  solution,  or  in  Ringer's  solution.     Mount  under  cover-glass 
and  study  carefully,  noting  position  of  nuclei,  longitudinal  myofibrils, 
and  cross  striations  (J  or  isotropic  discs;  Q  or  anisotropic  discs,  and 
ground  membranes  or  membranes  of  Krause).    By  exerting  pressure  on 
cover-glass,  crush  some  of  the  fibers.    Look  for  the  sarcolemma  spanning 
a  break  in  the  sarcoplasm.     (This  is  especially  readily  demonstrated  in 
the  frog's  muscle.)     Add  drop  of  dilute  acetic  acid  and  note  effect.    Then 
add  a  drop  of  the  methylene  blue  stain,  observe  the  shape  and  position 
of  the  nuclei,  and  sketch  (93)  a  fiber,  including  the  sarcolemma  at  the 
level  of  fracture. 

(2)  Study  fibers  from  a  macerated  preparation,  preserved  in  the 
alcohol-glycerin  mixture.     Note  the  terminal  cleavage  of  some  of  the 
fibers  into  discoid  structures,  the  sarcomeres ;  and  the  splitting  of  others 
into  the  constituent  myofibrillae    (sarcostyles).      Sketch    (94)    a  fiber 
showing  cleavage  into  sarcomeres  and  (95)  one  showing  splitting  into 
sarcostyles. 

(3)  Study   a   stained   transverse   section   of   striped   muscle    (e.g., 
tongue;  skeletal  muscle).    Draw  (96)  a  number  of  adjacent  fibers,  indi- 
cating nuclei,  myofibrils,  Cohnheim's  areas   (Kolliker's  columns),  and 
sarcolemma.     Sketch  (97)  a  fiber  in  longitudinal  section,  showing  the 
several  cross  striations.    How  do  the  cross  striations  in  striped  voluntary 
muscle  differ  from  those  in  cardiac  muscle? 

(4)  Make  drawing  (98)  of  a  portion  of  a  longitudinal  section  of 
some  arthropod  striped  muscle  fiber   (e.g.,  insect  leg  or  wing  muscle) 
from  a  demonstration  preparation,  showing  several  phases  in  the  con- 
traction process.     Note  the  several  striations:  isotropic  and  aniostropic 
discs,  Z  and  M  membranes  (telophragmata  and  mesophragmata)  ;  and 
the  additional  stripes  of:    (a)   the  accessory  disc   (of  von  Eollet  and 
Englemann)  and  (b)  the  resulting  terminal  disc  (of  Merkel).    Explain 
different  arrangement  of  the  striations  in  contracted  and  extended  fibers. 
Difference  between  a  contraction  'band'  and  a  contraction  'wave'? 

(5)  Sketch   (99)   l.p.  a  portion  of  a  transverse  section  of  a  small 


DIRECTIONS  FOB  LABORATORY  WORK  779 

muscle,  showing  epimysium,  muscle  fasciculi  and  enveloping  perimy- 
sium,  individual  fibers  and  enveloping  endomysium. 

(6)  Study  an  injected  specimen  of  skeletal  muscle  in  a  stained  longi- 
tudinal section.  Draw  (100)  a  few  fibers  showing  the  abundant  distri- 
bution and  intimate  disposition  of  capillaries  and  arterioles. 

(D)     TENDON. 

(1)  Study  a  stained  transverse  section  of  a  tendon.     Note  epitendi- 
neum,  peritendineum  enveloping  the  tendon  fasciculi,  and  the  endo- 
tendineum.    Make  a  sketch  of  same  under  the  low  power  (101).    Sketch 
(102)  h.p.  small  area  of  a  transversely  cut  tendon  bundle.     Note  the 
shape  of  the  tendon  cells  and  their  relation  to  the  smallest  subdivisions 
(primary  bundles)  of  the  fasciculi.     Sketch  (103)  two  adjacent  tendon 
fasciculi,  from  a  stained  longitudinal  section.    Note  peritendineum;  the 
disposition  of  the  cells  with  respect  to  the  tendon  bundles,  and  to  each 
other;  and  the  disposition  of  the  nuclei  in  successive  cells.     Genetic 
relationship  between  tendon  and  muscle? 

(2)  Study  the  area  of  junction  between  muscle  and  tendon,  from  a 
stained  longitudinal  section  (e.g.,  leg  muscle  of  frog).     Sketch  (104). 
What  is  the  relation  of  the  tendon  fibrils  to  the  muscle  fibrils?  to  the 
sarcolemma?     Note  the  increased  abundance  of  nuclei  at  this  level. 
Significance?     Two  chief  modes  of  muscle-tendon  connections? 

(3)  Sketch    from    specially    prepared    demonstration    slides:     (a) 
neuromuscular    (sensory)    end  organ,   or  muscle   spindle    (105) ;    (d) 
neurotendinous    (sensory)    end  organ,   or  tendon  spindle    (106) ;    (c) 
motor  end  plate  (107). 

VIII.    NERVOUS  TISSUE 

(A)  THE  NEURON  (Nerve  cell). 

(1)  Study  under  cover-glass  an  isolated  nerve  cell  (neurocyte)  from 
a  macerated  preparation,  or  a  teased  fresh  specimen,  of  the  gray  matter 
of  the  spinal  cord  of  the  ox.    Add  a  drop  of  stain.    Sketch  (108)  a  com- 
plete cell,  noting  axon,  dendrons,   axon  hillock    (implantation  cone), 
nucleus,   nucleolus,    and   granular   and   fibrillar   cytoplasmic    contents. 
What  are  the  marks  of  differentiation  between  an  axon  and  the  den- 
drons ? 

(2)  Sketch   (109)  a  similar  cell  from  a  stained  transverse  section 
of  the  spinal  cord. 


780  DIRECTIONS  FOR  LABORATORY  WORK 

(3)  Sketch  (110)  a  large  nerve  cell  (e.g.,  large  pyramidal  cell  of 
cerebral  cortex)  in  a  demonstration  slide  prepared  by  the  Beilschowsky 
technic  to  show  neurofibrils. 

(4)  Sketch  (111)  a  similar  cell  from  a  demonstration  preparation 
stained  by  Nissl's  method  to  show  the  chromophilic  substance    (Nissl 
granules,  chromophilic  granules,  tigroid  substance). 

(5)  Sketch  also   (112)  from  Golgi  preparation   (a)   a  large  pyra- 
midal cell  of  the  cerebral  cortex;  and  (113)   (b)  a  Purkinje  cell  of  the 
cerebellar  cortex. 

(B)     THE  AXON  ('Nerve  fiber';  Axis  cylinder  process;  Neurite). 

(a)  Medullated. —  (1)  Tease  in  Einger's  solution  a  fragment  of  a 
fresh  medullated  (myelinated)  nerve  (e.g.,  great  sciatic;  peroneal)  from 
a  mammal  or  the  frog.  Mount  under  a  cover-glass  and  study  a  well- 
preserved  fiber,  noting  the  axial  axis  cylinder  and  neuroplasm,  the  en- 
veloping medullary  (myelin)  sheath,  the  peripheral  nucleated  sheath  of 
Schwann  (neurolemma),  and  the  nodes  of  Eanvier.  Add  a  drop  of  some 
nuclear  stain,  and  sketch  (114).  Are  all  of  the  fibers  myelinated?  Are 
all  of  the  same  girth? 

(2)  Tease  a  fragment  of  a  medullated  nerve  preserved  in  osmic 
acid.     Mount  and  study  an  individual  fiber,  noting,  besides  the  above- 
specified  constituents,  also  the  Schmidt-Lantermann  lines  or  incisures. 
What  is  the  significance  of  the  Lantermann  segments?     Sketch  (115). 

(3)  Sketch  (116)  a  small  area  from  a  stained  cross  section  of  the 
white  matter  of  the  spinal  cord.    Note  the  central  axis  cylinder  and  the 
enveloping  myelin  sheath,  with  its  neurokeratin  framework.    Is  a  neuro- 
lemma present?    Note  also  the  neurogliar  connective  tissue  filling  the 
spaces  between  the  fibers. 

(4)  Study  under  l.p.  a  cross  section  of  a  large  medullated  nerve 
(e.g.,  tibial;  peroneal)  in  a  stained  preparation.     Sketch  (117)   show- 
ing epineurium,  perineurium,  funiculus,  endoneurium,  Henle's  sheath, 
and  nerve  fibers.    Sketch  h.p.  (118)  a  small  area  of  a  funiculus.    Are 
all  the  fibers  of  the  same  girth?    Sketch  (119)  also  several  fibers  from 
a  stained  transverse  section  of  a  medullated  nerve  preserved  in  osmic 
acid.     Chemical  character  of  myelin? 

(5)  Study  under  l.p.  a  longitudinal  stained  section  of  a  medullated 
nerve.     Sketch  (120)  a  small  extent  of  two  adjacent  funiculi.     Sketch 
under  h.p.   (121)  several  adjacent  fibers  showing  at  least  one  node  of 
Eanvier.    What  are  the  criteria  for  distinguishing  between  longitudinal 


BISECTIONS  FOR  LABORATORY  WORK  781 

section  of  a  medullatcd  nerve,  a  tendon  or  compact  white  fibrous  tissue 
and  smooth  muscle? 

(b)  Non-Medullated  Axon  (R&mak's  fibers;  Unmyelinated  fibers). 
—  (1)  Search  for  sympathetic  (autonomic)  nerves,  both  transversely  and 
longitudinally  cut,  in  a  stained  section  of  some  portion  of  the  alimentary 
tract,  in  the  connective  tissue"  between  the  two  muscle  layers.  Note  also 
an  occasional  sympathetic  ganglion  cell.  Sketch :  (a)  a  bundle  of  fibers 
cross  cut  (122)  ;  (b)  longitudinally  cut  (123)  ;  and  (c)  several  ganglion 
cells  (124).  Study  also  a  cross-section  of  the  trunk  of  the  vagus  nerve; 
here  non-medullated  fibers  are  mixed  with  medullated  fibers  of  all  sizes. 
Sketch  (125).  Tease  a  fragment  of  the  vagus  nerve  in  Einger's  solu- 
tion. Add  a  drop  of  stain.  Differentiate  between  the  myelinated  and 
unmyelinated  fibers  and  sketch  (126)  a  few  of  the  latter. 

(C)  GANGLIA. 

(a)  Spinal  (Dorsal,  Sensory). —  (1)    Study  a  stained  section  of  a 
spinal  ganglion.     Sketch  (127)  several  cells.     Note  nucleated  capsule. 
How  is  this  capsule  related  to  the  dendrons  and  to  the  neurolemma  of 
the  axon  ?    Compare  these  cells  with  those  of  the  sympathetic  ganglia. 

(2)  Sketch  (128)  the  several  types  of  atypical  cells  in  a  spinal  or 
cerebral  ganglion  (e.g.,  Gasserian)  in  a  specially  prepared  section  (Ran- 
son-CajaPs  pyridin-silver  method).  Note:  (a)  'fenestrated'  cells;  (b) 
multipolar  cells;  (c)  cells  with  collaterals  ending  in  'end  bulbs';  and 
(d)  the  usual  unipolar  type.  Explain  the  origin  of  the  unipolar  type. 
Which  of  the  two  divisions  of  its  single  process  corresponds  to  a  den- 
dron? 

(b)  Sympathetic  (Autonomic). —  (1)  Sketch  (129)  small  area  of  a 
sympathetic  ganglion  (e.g.,  ciliary;  otic;  ganglia  of  myenteric  plexus). 
Are  the  cells  of  the  sympathetic  ganglia  enveloped  by  a  nucleated  cap- 
sule? 

(D)  NEUROGLIA. 

Study  a  section  of  the  cerebral  cortex  or  spinal  cord  treated  accord- 
ing to  the  Golgi  technic  for  neuroglia.  Sketch :  (a)  a  larger  long-rayed 
astrocyte  (130)  ;  (b)  a  smaller  short-rayed  astrocyte  or  mossy  cell 
(131).  Study  a  second  section  treated  according  to  the  Benda  or  Wei- 
gert  neuroglia  technic.  Sketch  (132)  a  few  cells  and  fibers.  What 
structure  in  ganglia  is  the  homologue  of  the  neuroglia  of  the  brain  and 
spinal  cord?  What  is  the  analogue? 


782  DIEECTIONS  FOR  LABORATORY  WORK 

(E)     PERIPHERAL  NERVE  TERMINATIONS  (END-ORGANS). 

(a)  Nerve  Endings  in  Epithelium. —  (1)  Sketch  (133)  a  bundle  of 
naked  nerve  end-fibrils  in  a  demonstration  slide  of  thick  skin  or  cornea, 
stained  by  the  intravitain  methylene-blue  method.    In  the  same  prepara- 
tion search  for  tactile  cells  of  Merkel.    Note  tactile  meniscus  at  end  of 
nerve  fibril  and  the  associated  tactile  cell.     Sketch  (134). 

(2)  Sketch  (135)  a  taste  bud  from  a  circumvallate  papilla  of  the 
human  tongue  or  a  foliate  papilla  of  the  tongue  of  the  rabbit,  in  stained 
section.  Note  the  gustatory  cells,  the  sustentacular  cells  and  the  basal 
cells;  and  in  specially  stained  preparation  note  also  the  nerve  fibrils 
terminating  in  relation  to  the  cells  of  the  taste  bud. 

(b)  Nerve  Endings  in  Connective  Tissue. —  (1)  Study  a  stained  sec- 
tion of  skin  of  finger  tip.     Distinguish  between  vascular  and  tactile 
papillae  of  the  derma.     Sketch  (136)  a  tactile  corpuscle  (of  Meissner) 
from  a  tactile  papilla. 

(2)  Sketch  (137)  a  lamellar  (Pacinian)  corpuscle  from  a  stained 
toto  mount  of  a  fragment  of  the  cat's  mesentery.  Sketch  (138)  a  sim- 
ilar corpuscle  in  section  in  the  interlobular  connective  tissue,  from  a 
stained  section  of  the  pancreas.  Sketch:  (a)  a  corpuscle  of  Herbst 
(139)  ;  (b)  a  corpuscle  of  Grandry  (140),  from  a  stained  section  of 
duck's  bill. 

(c)  Nerve  Endings  in  Striped  Muscle  and  in  Tendon. —  (1)  sensory; 
muscle  spindles  and  tendon  spindles. 

(2)  motor;  motor  end-plates  in  muscle. 

Study  and  sketch  (141)  from  special  demonstration  slides.  What  is 
the  character  of  the  sole  plate?  relation  to  'intermediate'  or  'receptor* 
substance  of  myoneural  junction?  function  of  the  different  nerve  end- 
organs  ?  ( Consult  following  scheme  of  classification,  arranged  in  accord- 
ance  with  the  terminology  proposed  by  Sherrington.) 


DIRECTIONS  FOR  LABORATORY  WORK 


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784  DIRECTIONS  FOR  LABORATORY  WORK 

IX.  THE  BLOOD  VASCULAR  SYSTEM 

(A)  ARTERIES. 

(1)  MEDIUM-SIZED  ARTERIES    (the  larger  peripheral  arteries,  e.g., 
the  carotids,  femoral,  radial,  popliteal,  etc.).     Study  the  vessel  as  a 
whole,  in  a  stained  transverse  section,  noting  its  circular  outline,  the 
generally  empty  lumen,  the  corrugated  inner  surface,  and  the  thickness 
of  the  wall  relative  to  the  diameter  of  the  lumen.     Make  a  l.p.  sketch 
(142)  of  entire  vessel,  indicating  the  three  tunics:   (a)   tunica  interna 
(intima) ;    (b)    tunica  media,   and    (c)    tunica   externa    (adventitia). 
Sketch  h.p.  (143)  a  narrow  segment  of  the  wall,  noting  the  fundamental 
tissues  of  the  several  layers.     Identify  the  internal  and  external  elastic 
(fenestrated)  membranes,  and  the  vasa  and  nervi  vasorum  of  the  tunica 
externa.     "Which  is  the  thickest  tunic  and  what  tissue  elements  does  il 
include  ? 

(2)  LARGE   ARTERIES    (e.g.,   the   aorta). — Study  the  wall  of   the 
aorta  in  stained  section.     Sketch  h.p.    (144)    a  segment  of  the  wall. 
Compare  with  wall  of  medium  sized  artery.     Note  the  relatively  wider 
tunica  interna,  the  much  narrower  tunica  externa,  the  apparent  absence 
of  the  internal  and  external  elastic  membranes,  and  the  great  abundance 
of  elastic  tissue  among  the  muscle  cells  of  the  tunica  media.    Study  also 
a  similar  section  stained  with  some  specific  elastic  tissue  stain   (e.g., 
resorcin-fuchsin),  and  note  the  elastic  fibers  in  the  three  tunics.     Com- 
pare aorta  with  some  other  large  (conducting)  artery,  e.g.,  subclavian 
and  common  iliac. 

(B)  VEINS. 

(1)  MEDIUM-SIZED  VEINS  (the  larger  peripheral  veins,  e.g.,  exter- 
nal jugular,  basilic,  median,   femoral,  etc.).      Study  the   vessel   as  a 
whole,  in  stained  transverse  section,  and  note  its  relatively  thinner  wall 
as  compared  with  a  medium-sized  artery,  its  generally  collapsed  condi- 
tion, and  its  lumen  frequently  filled  with  blood.     Compare  in  detail 
with  a  medium-sized  artery,  noting  differences  in  composition  and  rel- 
ative thickness  of  the  several  tunics.    Sketch  l.p.  (145)  the  entire  vessel, 
indicating  the  three  tunics.    Sketch  h.p.  (146)  a  narrow  segment  of  the 
wall,  noting  the  fundamental  component  tissues  in  each  tunic.    Note  the 
delicate  character  of  the  internal  and  external  elastic  membranes. 

(2)  LARGE  VEINS,     (a)  The  Inferior  Vena  Cara. — Study  the  wall 
in  a  stained  section.     Compare  with  aorta.     Note  great  thickness  of 


DIRECTIONS  FOB  LABORATORY  WORK  785 

tunica  externa.  Sketch  h.p.  (147)  a  segment  of  the  wall,  noting  the 
fundamental  tissues  in  each  tunic.  Note  the  longitudinal  muscle  bun- 
dles in  the  tunica  externa.  Compare  with  portal  vein;  with  hepatic 
vein. 

(b)  The  Superior  Vena  Cava.  Sketch  h.p.  (148)  a  segment  of  a 
section  stained  with  a  specific  elastic  tissue  stain  noting  the  distribution 
of  elastic  fibers.  Compare  with  pulmonary  vein. 

(3)  VALVES.  Study  a  longitudinal  stained  section  of  a  large  peri- 
pheral vein  of  the  lower  extremities  (e.g.,  long  saphenous  vein).  Iden- 
tify the  valves,  and  note  their  distribution,  position  with  respect  to 
tributaries,  and  their  gross  and  minute  structure.  Sketch  (149)  a  seg- 
ment of  the  wall,  including  a  valve.  How  many  cusps  are  generally 
included  in  a  valve?  Why  are  valves  less  numerous  in  the  veins  of  the 
upper  than  lower  extremities,  and  why  are  they  entirely  lacking  in  the 
abdominal  and  thoracic  veins,  and  in  veins  of  smaller  calibre  than  2 
mm.?  What  specific  structural  differences  obtain  among  the  following 
veins :  venae  cavae,  mesenteric,  external  jugular,  pulmonary,  umbilical 
and  cranial?  What  is  the  functional  significance  of  these  differences? 

(C)     SMALL  VASCULAR  CO  MITES. 

(1)  SMALL  ARTERIES  AND  VEINS.    Many  sections  will  contain  pairs 
of  smaller  vessels.     Study  a  larger  pair  in  a  stained  section,  and  make 
detailed  comparison  with  respect  of  relative  gross  size  and  form,  con- 
dition of  lumen,  thickness  of  wall  relative  to  diameter  of  bore,  and  rela- 
tive thickness  of  the  several  tunics.    What  can  you  determine  regarding 
the  presence  of  elastic  membranes?    Make  (a)  l.p.  sketch  of  pair  (150)  ; 
(b)  h.p.  sketch  of  segment  of  wall  of  each  (151). 

(2)  ARTERIOLES  AND  VENULES. —  (a)  Find  a  pair  of  vascular  comites 
of  this  size  in  almost  any  stained  section.    Make  h.p.  sketch  (152),  not- 
ing especially  relative  thickness  of  the  several  tunics  in  the  vessels  of 
the  pair. 

(b)  In  a  stained  toto  mount  of  the  mesentery  or  the  pia  mater  find 
a  typical  pair  of  comites  and  trace  from  arteriole  and  venules  through 
precapillary  twigs  into  the  capillaries.     Sketch   (153)   such  a  system, 
noting  the  differential  marks  between  arteriole  and  venule,  precapillary 
artery  and  vein;  and  between  the  foregoing  and  capillaries.     What  are 
sinusoids?    Eetia  mirabilia?    How  do  they  differ  from  capillaries? 

(c)  In  stained  sections  identify  precapillary  arteries  and  veins  and 
capillaries.     Sketch   (154).     What  is  the  chief  differential  feature  be- 
tween a  precapillary  artery  and  vein,  and  between  these  and  a  capillary? 


786  DIRECTIONS  FOR  LABORATORY  WORK 

(d)  In  a  toto  mount  of  mesentery,  treated  with  silver  nitrate,  sketch 
(155)  the  endothelial  lining  of  one  of  the  smaller  vessels. 

(e)  Sketch  (156)  in  longitudinal  or  oblique  section  a  capillary,  and 
a  precapillary  vein  in  the  bone  marrow  of  a  developing  membrane  bone, 
e.g.,  jaw  of  pig  fetus  of  35  mm. 

(At  this  stage  the  student  should  review  his  slides,  noting  in  each 
section:  (a)  the  type  of  epithelium  present;  (b)  the  type  of  connective 
tissue;  (c)  muscle;  (d)  nerves;  and  (e)  types  of  blood  vessel.  Several 
laboratory  periods  may  be  spent  to  advantage  on  this  exercise.) 

(D)     HEART  (Cor). 

(1)  Make  gross  study  of  heart  (human,  hog,  dog  or  beef)  and  note 
in  intact  organ:   (a)   ventricles,   (b)   atria,   (c)   auricular  appendages, 

(d)  pericardium  (visceral  and  parietal  portions),  and  (e)  the  roots  of 
the  several  large  arteries  and  veins   (aorta,  pulmonary  artery,  inferior 
and  superior  vena  cava,  and  the  pulmonary  veins).     Open  the  several 
chambers  and  note  in  the  ventricles:  (a)  columnas  carnese,  (b)  papillary 
muscles,  (c)  chordae  tendinese,  attached  to  the  valves  guarding  the  atrio- 
ventricular  orifices,  (d)  the  moderator  band  of  the  right  ventricle,  and 

(e)  the  semilunar  valves  guarding  the  aortic  and  pulmonary  orifices.    In 
the  atria  note  the  (a)  pectinate  muscles  of  the  auricular  appendages  and 
(b)  the  crista  terminalis.     Note  also  the  interatrial  and  the  interven- 
tricular  septa,  and  expose  the  atrio-ventricular  bundle  (bundle  of  His) 
in  the  anterior  septal  portion  of  the  heart. 

(2)  Study  a  stained  transverse  section  of  the  heart  of  a  mouse  (or 
other  small  mammal)  cut  through  the  ventricles.    Note  (a)  epicardium, 
(b)  myocardium,  (c)  endocardium,  (d)  papillary  muscles,  (e)  columns 
carnese.     Sketch  under  l.p.   (157). 

(3)  Study  a  stained  section  through  the  ventricular  wall  of  the 
human  heart.     Note  the  several  layers,  and  compare  with  the  three 
tunics  of  a  large  blood  vessel.     Make  l.p.  sketch  (158). 

(4)  From  stained  sections  make  h.p.  sketches  of   (a)   epicardium 
(159),  (b)  endocardium  (160),  (c)   Purkinje  fibers,  in  transverse  sec- 
tion (most  conspicuous  in  rabbits  and  sheep's  heart)   (161),  and  a  cusp 
of  an  atrio-ventricular  valve,  including  base    (annulus  fibrosus)    and 
apex,  noting  in  each  case  the  component  tissue  elements  (162). 

(5)  Make  drawings  from  demonstration  preparation  of  the  node  of 
the  sino-ventricular  bundle,  showing  the  constituent  muscular  and  con- 
nective tissue  elements  (163),  and  the  nerve  and  blood  supply  (164). 
Structure  of  sino-ventricular  bundle  of  His?  of  the  moderator  band? 


DIRECTIONS  FOR  LABORATORY  WORK  787 

(6)  Sketch  small  area  of  myocardium  from  injected  specimen  of 
cat's  heart  to  show  vascular  supply   (165). 

(7)  Sketch  from  a   demonstration  slide    (stained  with   methylene 
blue)  a  small  area  of  the  myocardium,  showing  the  manner  of  the  nerve 
supply  (166). 

X.     BLOOD 

(A)     THE  RED  BLOOD  CORPUSCLES  (Eryihroplastids,  'Erythro- 
cytes') . 

(1)  Sterilize  tip  of  finger  or  lobe  of  ear  with  an  alcohol-ether  solu- 
tion, and  allow  to  dry  thoroughly.     Sterilize  a  needle  in  the  flame  of  a 
Bunsen  burner.    Prick  finger  tip  or  lobe  of  ear,  and  mount  a  consider- 
able drop  of  blo<pd  under  a  cover-glass.     Examine  quickly.     Compare 
color  as  viewed  macroscopically  and  under  the  microscope.     Note  shape 
and  form  of  red  corpuscles,  as  seen  en  face  and  in  profile.     Note  the 
formation  of  rouleaux.    Sketch  (167).    After  a  time  crenated  corpuscles 
appear  near  the  edges  due  to  evaporation  of  the  blood  plasma  which  in 
consequence  has  become  hypertonic.    Sketch  (168).    Note  also  the  white 
glistening  leucocytes,  and  the  clumps  of  platelets. 

(2)  Place  011  a  slide  a  small  drop  of  Ringer's  solution  (an  isotonic 
solution).     Prick  finger  tip  and  touch  a  small  drop  of  blood  to  the 
Ringer's  solution.     Mount  the  mixture  under  a  cover-glass  supported 
by  a  hair  (or  prepare  the  mixture  on  the  cover-glass  and  mount  as  a 
hanging  drop  over  a  hollow  ground  slide,  sealing  the  cover-glass  with 
vaselin).     Follow  a  red  corpuscle  as  it  floats  and  turns  in  a  current, 
noting  carefully  its  form.    What  is  the  shape  of  the  red  blood  corpuscle  ? 
Is  it  nucleated?  Sketch   (169).     What  is  the  significance  of  the  cup- 
shaped  corpuscles?  Sketch   (170).     Do  rouleaux  appear  in  the  circu- 
lating blood?    Note  also  the  white  glistening  round  and  irregular  leu- 
cocytes, and  the  granular  masses  of  platelets. 

(3)  Make  successive  mounts  of  blood  in  Ringer's  solution  and  add 
to  (1)  a  drop  of  a  one  per  cent  solution  of  acetic  acid;  to  (2)  a  drop 
of  a  one  per  cent  solution  of  tannic  acid;  to  (3)  a  drop  of  a.  solution  of 
bile.    Note  the  results  and  explain.    How  is  the  third  result  related  to 
the  morbid  condition  known  as  jaundice  or  icterus? 

(4)  Mount  a  drop  of  blood  in  distilled  water  (a  hypotonic  solution). 
Follow  the  successive  changes  undergone  by  the  red  corpuscles.    Sketch 
(171).     Explain.     Recognize  the  final  steps  when  blood  shadows  and 
blood  dust  (hemokonia)  appear. 


788  BISECTIONS  FOE  LABORATORY  WORK 

(B)  THE  WHITE  BLOOD  CELLS  (Leucocytes;  Amebocytes). 

(1)  Mount  a  drop  of  blood  in  Toison's  solution  under  cover-glass. 
Note  the  several  types  of  white  blood  cells:  (a)  small  mononuclear;  (b) 
large  mononuclear;  (c)  polymorphonuclear ;  and  (d)  note  also  a  group 
of  blood  platelets  (plaques).    Are  the  latter  elements  capable  of  ameboid 
motility?     What  is  their  derivation?     Are  they  true  cells?     What  is 
their  most  probable  function? 

(2)  Study  carefully  with  oil  immersion  lens  a  blood  smear  stained 
with   Wright's    (or   Basting's,   Ehrlich's   triacid,   or   Jenner's)    stain. 
Identify  and  sketch  (172)  the  various  types  of  leucocytes:  (a)  lympho- 
cytes (large  and  small)  ;  (b)  large  mononuclear  and  'transitional'  non- 
granular  leucocytes;  (c)  polymorphonuclear  neutrophil  leucocyte;   (d) 
eosinophil  leucocyte;  (e)  basophil  leucocyte  (mast  cell);  and  (f)  blood 
platelets.    Note  relative  size,  shape  of  nuclei,  granular*  cytoplasmic  con- 
tent, and  relative  abundance  of  each  type.     Make  similar  study  of  rab- 
bit's blood.     (Here  the  neutrophils  are  replaced  by  similar  cells  witli 
fine  eosinophilic,  'special',  granules.    In  amphibia  and  reptiles  the  neu- 
trophils are  replaced  by  eosmophils  with  ellipsoidal  granules.) 

(3)  Study  the  contents  of  a  vein  in  a  stained  section.    Note  the  vari- 
ous shapes  of  the  red  corpuscles,  and  identify  the  white  blood  cells  present. 

(4)  Make  mount  in  Toison's  solution  of  frog's  blood.     Note  the 
ellipsoidal  nucleated  red  corpuscles,  the  white  blood  cells  (a,  small,  large 
and  'transitional'  non-granular  leucocytes;  b,  polymorph  neutrophils; 
c,  eosinophils;  and  d,  basophils)  and  the  small  spindle-shaped  throm- 
bocytes.     Sketch  (173).     Watch  a  large  leucocyte  in  ameboid  progres- 
sion.    Sketch  several  steps  (174). 

(5)  Make  similar  mount  and  study  of  bird's  or  turtle's  blood.    How 
does  it  differ  from  frog's  blood?    How  do  sauropsid  bloods  differ  from 
mammalian?  rabbit's  blood  from  human  blood? 

(C)  FIBRIN. 

Place  a  small  drop  of  blood  on  slide  and  spread  out  thin,  allow 
to  coagulate  slowly.  Breathe  on  the  coagulum  at  intervals  through 
a  period  of  about  a  quarter  of  an  hour.  Add  a  drop  of  methylene 
blue,  and  allow  it  to  act  for  several  minutes.  Rinse  in  water;  dry 
thoroughly  and  mount  under  a  cover-glass  in  balsam.  Examine  the 
thinner  portions  of  the  coagulum  for  the  fibrin  net.  Sketch  (175). 
Study  and  sketch  (176)  also  a  small  area  of  the  fibrin  net  from  a 
stained  section  of  a  blood  clot.  Difference  between  plasma  and  serum? 


DIRECTIONS  FOE  LABORATORY  WORK  789 

(D)  HEMOGLOBIN  CRYSTALS. 

Place  large  drop  of  blood  on  slide  in  a  small  drop  of  distilled  water. 
Allow  to  dry  slowly.  Mount  when  dry  in  balsam  under  cover-glass.  Ex- 
amine h.p.  for  crystals.  Note  shape,  size  and  color.  Sketch  (177). 

(E)  HEM  IN  CRYSTALS. 

Place  a  drop  of  blood  on  slide.  Add  2  or  3  grains  of  sodium  chloride 
and  a  drop  of  glacial  acetic  acid.  Heat  slowly  over  flame  of  a  Bunsen 
burner  until  bubbles  begin  to  appear.  Mount  in  balsam.  Examine  h.p. 
for  crystals.  Note  shape,  size  and  color.  Sketch  (178)  several  isolated 
crystals  and  several  groups. 

(F)  BLOOD  DEVELOPMENT  (Hemopoiesis). 

(1)  IN  EMBRYO.     Sketch   (179)   a  few  blood  cells  from  a  young 
mammalian  embryo,  noting  the  several  types  of  embryonic  erythrocytes : 
(a)   hemoblasts,   (b)   erythroblasts,   (e)   normoblasts. 

(2)  IN  ADULT  BONE  MARROW.    Study  with  oil  immersion  lens  smear 
preparation  or  a  section  of  red  bone  marrow  (e.g.,  of  femur  of  rabbit  or 
guinea  pig),  stained  in  Wright's  solution.     Identify  and  sketch  (180) 
the  several  types  of  myelocytes:    (a)    myeloblast,    (b)    leucoblast,    (c) 
erythroblast ;  also  (d)  myeloplaxes  (giant  cells),  (e)  erythrocytes,  (f) 
the  several  types  of  granular  myelocytes:  eosinophil,  basophil  and  'spe- 
cial' (neutrophil  of  higher  mammals),  and  (g)  origin  of  platelets  from 
pseudopods  of  megakaryocytes.     Note  cells  in  process  of  division,  both 
mitotic  and  amitotic.    Note  also  the  framework  of  reticular  connective 
tissue   (reticulum)  ;  and  the  process  of  extrusion  of  the  nucleus  of  a 
normoblast  in  the  formation  of  an  erythroplastid.     Compare  with  sec- 
tion of  red  marrow  of  femur  of  frog.    Differences  ?    Make  similar  study 
of  fragment  of  marrow  of  femur  of  rabbit  or  guinea  pig,  preserved  in 
aceto-carmin,  and  teased  in  glycerin. 


XI.    THE  LYMPHATIC  SYSTEM 

(A)  LYMPH. 

Study  a  smear  preparation  of  lymph  stained  with  Wright's  stain 
from  the  thoracic  duct  of  a  dog.  Sketch  (181)  the  several  types  of 
leucocytes.  Which  type  predominates?  Do  blood  platelets  occur  in 
lymph  ?  Bed  blood  corpuscles  ?  Origin  of  lymph  ?  Consider  the  coagu- 
lation of  lymph. 


790  DIRECTIONS  FOR  LABORATORY  WORK 

(B)  LYMPH  VESSELS  (lymphatics). 

(1)  LYMPH  CAPILLARIES.     Identify  a  lymph  capillary  in  a  stained 
section  (e.g.,  lymph  node,  subcutaneous  tissue,  submucosa  of  trachea  or 
large  intestine)   and  sketch   (182).     How  does  it  differ  from  a  blood 
capillary?  a  venule?  a  sinusoid? 

(2)  LACTEAL.    Sketch  (183)  the  terminal  lymph  capillary  in  a  villus 
of  a  stained  section  of  the  small  intestine. 

(3)  THORACIC  DUCT.     Sketch   (184)   a  segment  of  the  wall  of  a 
stained  section  of  the  thoracic  duct  (Weigert's  elastic  tissue  stain,  and 
picric-acid-fuchsin).     Note  the  several  layers,  and  the  fundamental  tis- 
sues of  each.    How  can  you  distinguish  between  a  large  lymphatic  and 
a  vein  of  the  same  calibre?    Do  lymphatics  contain  valves? 

(C)  SEROUS  MEMBRANES    (Peritoneum,   Pleura,   and  Pericar- 

dium). 

Sketch  (185)  h.p.  a  small  area  of  a  stained  toto  mount  of  a  frag- 
ment of  the  peritoneum  treated  with  silver  nitrate.  Note  the  character 
of  cells  and  intercellular  stomata.  Sketch  (186)  also  a  short  segment 
of  a  stained  section  of  same.  Note  shape  and  character  of  cells;  inter- 
cellular bridges,  striated  border,  basement  membrane,  and  the  submeso- 
thelial  fibre-elastic  corium. 

(D)  LYMPH  NODULES  (Lymph  follicles). 

Sketch  (187)  l.p.  a  small  lymph  nodule  from  the  submucosa  of  a 
stained  section  of  large  intestine,  stomach,  or  vermiform  appendix. 

(E)  LYMPH  NODE  (Lymph  gland). 

Study  a  stained  section  of  a  mesenteric  lymph  node.  Sketch  (188) 
l.p.  Sketch  (189)  h.p.  small  area  including  a  medullary  cord  and  the 
adjacent  lymph  sinus.  What  is  the  predominant  cell  type  ?  Note  divid- 
ing cells  in  germinal  center  of  cortical  nodules.  Examine  in  Ringer's 
solution  scrapings  from  a  lymph  node  of  cat,  after  addition  of  drop  of 
methylene  blue.  Examine  also  a  glycerin  mount  of  aceto-carmin  pre- 
served material. 

(F)  LYMPHOID  ORGANS. 

(1)  HEMOLYMPH  NODE.  (Hemal  Node).  Study  a  stained  sec- 
tion of  a  hemolymph  node  of  sheep.  Sketch  (190)  h.p.  a  small  area 
including  the  denser  and  looser  parenchyma.  Differential  characteris- 


DIRECTIONS  FOB  LABORATORY  WORK  791 

tics  of  lymph,  hemal  and  hemolymph  nodes?    Blood  and  lymph  supply 
of  each?     Giant  cells? 

(2)  TONSILS  (Faucial  tonsil}.    Study  a  stained  section  of  the  faucial 
tonsil.     Make  h.p.  sketch   (191)   of  the  infiltrated  stratified  squamous 
epithelium  lining  a  crypt.     Function  of  tonsils? 

(3)  SPLEEN  (Lien). —  (a)  Study  a  stained  section  of  spleen.     Note 
(1)  robust  fibromuscular  capsule ;  (2)  similar  trabecula? ;  and  (3)  splenic 
(Malpighian)   corpuscles  with  central  or  subcentral  arteriole.     Sketch 
segment  under  l.p.  (192).    Study  under  h.p.  the  spleen  pulp,  noting  dif- 
ference between  pulp  cords  and  intercordal  pulp  (venous  sinuses).  Sketch 
(193)  a  small  area  of  this  portion  of  the  parenchyma,  noting  types  of 
cells  and  character  of  the  terminal  arterioles.     Study  injected  specimen 
of  spleen,  noting  vascular  terminals  within  the  lobule. 

(b)  From  a. smear  preparation  of  spleen,  stained  with  Wright's 
blood  stain,  sketch  (194)  the  several  types  of  parenchymal  cells:  (1) 
lymphocytes;  (2)  polymorphonuclear  neutrophil  leucocytes;  (3)  large 
mononuclear  leucocytes  ('splenic  cells')  ;  (4)  eosinophil  leucocytes;  (5) 
basophil  leucocytes;  (6)  erythrophages ;  (7)  erythroblast ;  (8)  giant 
cells.  Make  similar  study  of  an  aceto-carmin  preparation  mounted  in 
glycerin.  What  are  the  chief  criteria  for  distinguishing  the  several 
lymphoid  organs  from  lymph  glands,  and  from  each  other?  Functi<*n 
of  spleen? 

XII.    SKIN  AND  APPENDAGES 

(A)     THE  SKIN  (Integument). 

(1)  Study  under  l.p.  a  vertical  stained  section  of  thick  skin  (from 
palm  of  hand  or  sole  of  foot).    Note  epidermis  (cuticle),  dermis  (cor- 
ium,  cutis),  and  the  tela  subcutanea.    Distinguish  between  the  stratum 
corneum  and  the  stratum  germinativum ;  between  the  pars  papillare  and 
the  pars  reticulare.     Note  the  spiral  epidermal  portion  of  the  ducts  of 
the  sweat  glands.     Note  also  the  panniculus  adiposus  of  the  subcu- 
taneous tissue.     Sketch  a  narrow   segment  through   entire  thickness 
(195).    Make  h.p.  sketch  (196)  of  several  adjacent  cells  from  each  of 
the  six  distinct  layers  of  the  epidermis.     What  are  the  several  factors 
(physical,  chemical  and  mechanical)   which  operate  upon  a  cell  of  the 
cylindrical  cell  layer  during  its  metamorphosis  into  an  element  of  the 
scaly  cell  layer? 

(2)  Study  under  l.p.  a  vertical  stained  section  of  thin  skin  (e.g., 
from  abdomen).     Sketch  (197).    What  are  the  chief  structural  differ- 


792  DIRECTIONS  FOE  LABORATORY  WORK 

ences  between  thick  and  thin  skin?    Between  thin  skin  and  the  mucous 
membrane  lining  the  mouth?     Note  the  delicate  hairs. 

(3)  Make  h.p.  sketches  (198,  a,  b,  c)  from  different  portions  of  a 
section  through  the  head   of   a   20-mm.   pig  fetus,   illustrating  three 
earlier  stages  in  the  development  of  skin :  one  consisting  of  a  single 
layer  of  cells  (with  super  jacent  peri  derm  or  epitrichium),  one  of  two 
or  three  layers,  and  one  of  a  larger  number  of  layers. 

(4)  Compare  sections  of  thin  skin  of:   (a)   dark  negro;   (b)   light 
mulatto;  (c)  brunette;  (d)  blond.     Note  quantity  and  distribution  of 
the  pigment  (melanin)  granules  in  the  several  specimens  of  skin. 

(B)  SWEAT  GLANDS  (Sudoriparous  glands). 

(1)  In  a  stained  vertical  section  of  skin  identify  and  study  a  sweat 
gland  (complete  if  possible).  Note:  (a)  its  duct  (excretory)  including 
the  spiral  'mouth'  within  the  epidermis;  (b)  its  coiled  fundus  (secre- 
tory). Under  h.p.  draw  a  cross-section  of  the  dermal  (or  subcutaneous) 
duct  and  fundus  (199).  Note  the  longitudinally  disposed  smooth  mus- 
cle cells  between  the  secretory  cells  of  the  fundus  and  the  membrana 
propria. 

(C)  THE  NAILS  (Unguis;  Onyx). 

(1)  Examine  a  finger-nail  and  note:  (a)  body;  (b)  root;  (c)  lun- 
ula;  (d)  nail  sulcus;   (e)   nail  fold  or  vallum;   (f)   eponychium;   (g) 
hyponychium.     Sketch   (200).     Explain  the  opacity  and  color  of  the 
lunula. 

(2)  Study  l.p.,  a  stained  transverse  section  of  the  finger  tip  includ- 
ing the  nail.     Note  the  homologous  layers  of  nail  and  adjacent  skin. 
What  differences  obtain?     What  layer  of  the  epidermis  does  the  nail 
body  represent  ?    How  does  the  pars  papillare  differ  in  the  two  regions  ? 
Sketch  (201). 

(3)  Make  l.p.  sketch  (202)  of  a  stained  vertical  longitudinal  section 
of  the  unguinal  phalanx.    Note  nail  matrix  and  nail  bed.    What  is  the 
epidermal  homologue  of  the  nail  matrix?     The  relation  of  the  matrix 
to  the  lunula?    Sketch  (203)  h.p.  a  small  area  through  the  body  of  the 
nail  including  its  corium. 

(D)  THE  HAIR  (Pilus;  Thrix). 

(1)  Mount  in  water  under  cover-glass  a  freshly  extracted  hair. 
Note:  (a)  hair  bulb;  (b)  root  (radix);  (c)  shaft  (scapus) ;  (d)  me- 
dulla; (e)  cortex;  (f)  pigment  granules;  and  (g)  cuticle.  Explain 


DIRECTIONS  FOR  LABORATORY  WORK  793 

differences  in  color  of  hair.     Sketch  under  h.p.  a  portion  of  the  shaft 
(204). 

(2)  In  a  stained  vertical  section  of  the  scalp  examine,  under  the 
low  power,  a  hair  follicle  with  its  included  hair  in  longitudinal  section. 
Note:   (a)  hair  papilla;   (b)   hair  bulb   (pigmented?) ;   (c)   hair  root; 
(d)    epidermal  root  sheath;    (e)    arrector  pili  muscle;    (f)    sebaceous 
gland.     Sketch   (205).     Make  h.p.  sketch   (206)    of  the  hair  and  its 
follicle,  cut  longitudinally,  at  the  level  of  the  sebaceous  gland  (about 
the  middle  third  of  the  root),  noting  the  several  layers  of  the  inner 
and  outer  root  sheaths  (the  epidermal  sheath),  and  of  the  dermal  sheath. 
What  is  the  function  of  the  arrectores  pilorum  muscles?     Make  h.p. 
sketch  (207)  of  the  region  of  transition  from  root  and  follicle  to  the 
hair  bulb. 

(3)  Sketch  h.p.   (208)  a  transverse  section  of  a  hair  follicle  at  or 
near  the  level  of  the  middle  third,  showing  the  several  layers  of  the 
follicle  as  above.    What  layers  are  homologous  in  hair  follicle  and  skin? 
Explain  the  honiologies  in  terms  of  development.    Explain  the  cause  of 
the  curling  of  certain  types  of  hair. 

(E)  SEBACEOUS  GLAND. 

(1)  Study  a  sebaceous  gland  in  a  stained  vertical  section  of  the 
scalp.  Note  its  relation  to  the  hair  follicle.  Note  also  its  duct  and 
saccules.  Sketch  l.p.  (209).  Make  h.p.  sketches  (210  a,  b,  c)  of  cells 
of  the  sebaceous  gland  at  three  successive  stages  of  their  metamorphosis 
into  the  sebum  'secretion'.  How  many  glands  to  a  hair  follicle? 

(F)  THE  BLOOD  SUPPLY. 

(1)  Study  in  stained  section  injected  specimens  of  skin  and  scalp. 
Sketch  (211).  Note  the  precise  location  of  the  several  vascular  plexuses 
of  the  derma  and  the  tela  dubcutanea ;  and  the  blood  supply  of  the  sweat 
glands,  hair  follicles,  sebaceous  glands,  and  the  fat  lobules  of  the  tela. 

XIII.     THE  RESPIRATORY  SYSTEM 

( A )     THE  NA  8  A  L  CA  VITY. 

(1)  Study  in  a  stained  section  the  lining  mucous  membrane  of  the 
vestibule.    Note  transition  from  external  skin  to  internal  mucous  mem- 
brane; note,  also  the  vibrissae  and  the  associated  sebaceous  glands.    Makt 
h.p.  sketch  of  a  narrow  segment  (212). 

(2)  Study  mucosa  of  respiratory  portion  (Schneiderian  membrane). 


794  DIRECTIONS  FOR  LABORATORY  WORK 

Note  the  pseudo-stratified  ciliated  columnar  epithelium,  goblet  cells,  the 
extensive  vascular  corium,  and  the  sero-mucous  glands.  Sketch  h.p.  a 
narrow  segment  (213). 

(3)  Make  h.p.  sketch  (214)  of  olfactory  mucous  membrane,  noting: 
a,  sustentacular  cells;  b,  olfactory  cells;  c,  basal  cells;  and  d,  serous 
glands  of  Bowman.    In  what  respect  is  the  olfactory  cell  unique  ? 

(4)  In  a  section  of  the  cat's  nose,  note  the  vomero-nasal  organ  of 
Jacobson  in  the  median  septum,  one  on  either  side  of  the  cartilaginous 
plate.     Sketch  a  narrow  segment. 

(B)  THE  LARYNX. 

(1)  Study  a  stained  vertical  section  through  lateral  wall  of  the 
larynx.  Note  vocal  cords  (true  and  false)  and  ventricle.  Sketch  (215), 
indicating  the  types  of  epithelium  and  the  contents  of  the  corium  at 
different  levels.  What  are  the  fundamental  tissues  comprised  in  the 
true  vocal  cords? 

(C)  THE  TRACHEA. 

(1)  Study  a  stained  transverse  section  of  the  trachea.  Note:  a, 
character  of  the  lining  epithelium;  b,  goblet  cells;  c,  elastic  layer  in 
tunica  propria ;  d,  muscularis  mucosa?  ?  e,  tela  submucosa,  with  its 
mucous  glands  with  demilunes;  f,  fibre-cartilaginous  tunic.  Trace  the 
duct  of  a  mucus-secreting  gland  to  the  surface.  Note  its  apulla  in  the 
corium.  What  is  the  character  of  the  cartilage  of  the  adventitia?  Ex- 
plain the  trachealis  muscle.  Sketch  h.p.  (216)  a  narrow  segment  of 
the  complete  width  of  the  wall. 

(D)  THE  BRONCHI. 

(1)  Study  a  stained  transverse  section  of  a  primary  bronchus.  Com- 
pare with  trachea.  In  what  points  do  they  differ? 

(E)  THE  LUNG  (Pulmo}. 

(1)  Make  h.p.   sketch    (217)    of  narrow.,  segment  of  wall  of  sec- 
ondary or  tertiary  bronchus.    Note :  a,  muscularis  mucosae ;  b,  lymphoid 
tissue   (solitary  nodules?);  c,  mucous  glands;  d,  character  of  lining 
epithelium.    How  are  the  pulmonary  artery  and  vein,  and  the  bronchial 
artery  and  vein,  related  to  these  bronchi? 

(2)  Sketch  h.p.  (218)  a  bronchiole.    What  are  the  chief  structural 
differences  between  a  bronchiole  and  a  tertiary  bronchus?    Eelation  oi 
pulmonary  artery  and  vein  to  bronchiole?    Structure  of  terminal  (res- 
piratory) bronchiole? 


BISECTIONS  FOB  LABORATORY  WORK  795 

(3)  Make  l.p.  sketch    (219)    of  a  primary  lobule    (histologic  and 
functional  unit),  including:  a,  transition  from  respiratory  (terminal) 
bronchiole  to  b,  alveolar  duct ;  c,  atria ;  d,  pulmonary  sacs ;  e,  pulmonary 
alveoli.     Study  the  several  portions  of  the  primary  pulmonary  lobule 
under  the  high  power  and  note  the  structural  differences.    At  what  point 
in  the  lobule  does  the  smooth  muscle  end?     Where  do  the  lymphatics 
end?    Relative  abundance  of  the  elastic  fibers?    Relation  of  pulmonary 
artery  and  vein  to  the  primary  lobule?    Define  a  secondary  pulmonary 
lobule  (anatomic  unit). 

(4)  Make  h.p.  sketch  (220)  of  wall  of  pulmonary  alveolus  (air  cell) 
cut  tangentially.    Note  the  flat  respiratory  cells  and  the  expansive  non- 
nucleated  respiratory  plates. 

(5)  Sketch  (221)  several  adjacent  alveoli  from  a  section  of  an  in- 
jected specimen  of  the  cat's  lung. 

(6)  Make  h.p.  sketch  (222)  of  small  extent  of  the  visceral  pleura. 

(7)  Consider  the  distribution  of  the  lymphatics,  the  lymph  nodes, 
lymph  nodules  and  the  more  diffuse  lymphoid  tissue  in  the  lung.    Func- 
tion of  lymphoid  tissue  in  the  lung?     Relation  to  inhaled  dust?  to 
infecting  bacteria?  to  tuberculosis?    Consider  also  the  distribution  and 
relative  abundance  of  smooth  muscle  and  of  elastic  fibers.     Significance? 
Relation  to  asthma?  to  anaphylaxis,  e.g.,  in  guinea  pig?    Explain  ab- 
sence of  bronchial  veins  beyond  the  bronchioles. 

XIV.    THE  ALIMENTARY  TRACT 

(Digestive  Canal) 

(A)  THE  LIP. 

(1)  Study  l.p.  stained  section  (vertical)  of  lip.  Distinguish  cuta- 
neous and  mucous  surfaces.  Note :  a,  bundles  of  striped  muscle  fibers  of 
orbicularis  oris  muscle  in  transverse  section;  b,  mucous  glands;  c,  hair 
follicles;  d,  sweat  glands;  e,  sebaceous  glands;  f,  coronary  (labial)  ar- 
tery. Sketch  (2S3). 

(B)  THE  TEETH. 

(1)  Study  a  stained  axial  section  of  a  decalcified  molar  tooth  within 
its  alveolar  socket.  Note:  a,  crown;  b,  neck;  c,  root;  d,  fangs;  e,  pulp 
cavity;  f,  root  canal;  g,  foramen  apicis  dentis.  Sketch  h.p.  (224)  small 
area  of  a,  enamel ;  b,  dentin ;  c,  cementum ;  d,  dental  pulp  reticulum ;  e, 
granular  layer  of  Tomes ;  f ,  an  odontoblast  with  its  Tomes'  fibril  within 


796  DIRECTIONS  FOE  LABORATORY  WORK 

a  dentinal  tubule.  Sketch  l.p.  (225)  a  portion  of  the  area  of  contact 
between  root  of  tooth  and  alveolar  process.  Note:  a,  alveolar  bone;  b, 
periosteum  and  pericementum ;  c,  circular  dental  ligament;  d,  epithelial 
remnants  of  dental  lamina;  e,  fibers  of  Sharpey;  f,  cementum  cells. 

(2)  Study  l.p.  an  axial  ground  section  of  tooth.    Note  in  the  enamel, 
the  contour  lines  of  Eetzius  and  the  prism  stripes  of  Schreger;  in  the 
dentin,  the  dentinal  tubules,  the  contour  lines  of  Owen,  and  the  incre- 
mental lines  of  Schreger.     Make  h.p.  sketches  (226)  of  small  areas  of 
the  enamel  showing  the  prism  bundles  cut  transversely  and  longitudi- 
nally; also  (227)  of  small  areas  of  the  dentin'  showing  the  tubules  cut 
transversely  and  longitudinally.     Sketch  also  (228)  a  small  area  of  the 
cementum;  and  (229)  of  the  granular  layer  of  Tomes  in  the  region  of 
the  neck  of  the  tooth.     Describe  the  complete  form,  structure,  content 
and  significance  of  the  dentinal  tubules. 

(3)  Sketch  (230)  several  successive  early  stages  in  the  development 
of  the  deciduous  teeth  in  a  stained  vertical  section  of  the  jaw  of  some 
mammalian  fetus  "(e.g.,  of  25  mm.  pig  embryo).     Note:  a,  labiodental 
strand  and  groove ;  b,  labial  lamina ;  c,  dental  lamina ;  d,  enamel  organ ; 

e,  dental  papilla. 

(4)  Study  a  stained  axial  section  of  an  infant's  tooth  some  time 
before  eruption.     Note:  a,  enamel  organ  (enamel,  inner  enamel  epithe- 
lium, outer  enamel  epithelium,  and  enamel  pulp)  ;  b,  dental  pulp,  odon- 
toblasts  and  the  strata  of  older  and  younger  dentin;  c,  the  dental  sac; 
d,  anlage  of  the  permanent  tooth;  e,  remnant  of  the  dental  lamina. 
Make  l.p.  sketch  (231).    Sketch  h.p.  (232)  a  small  area  near  the  apex 
of  the  crown,  showing  from  without  inward :  a,  enamel  pulp ;  b,  layer  of 
ameloblasts;  c,  Tomes'  processes;  d,  enamel;  e,  membrana  perf ormativa ; 

f,  stratum  of  older  basophilic  dentin;  g,  stratum  of  younger  acidophilic 
(only  slightly  calcified)  dentin  with  Tomes'  fibrils;  h,  layer  of  odonto- 
blasts ;  i,  dental  pulp. 

(C.)     THE  TONGUE  (Lingua). 

(1)  Make  diagram  l.p.  (233)  of  transverse  section  of  a  cat's  tongue 
to  show  the  disposition  of  the  striped  muscle.    Note  the  bilaterally  sym- 
metrical structure  of  the  tongue;  the  extent  of  the  medial  septum  lin- 
guae; the  difference  between  the  mucous  covering  on  the  dorsum  and 
ventrum  of  the  tongue.     Note  also  the  superficial  longitudinal  muscles, 
the  genio-glossus  ventrally,  and  the  deep  transverse  and  vertical  fibers. 
Note  further  the  glands  imbedded  in  the  muscle. 

(2)  Sketch  from  stained  sections  of  the  human  tongue  the  several 


DIRECTIONS  FOR  LABORATORY  WORK  797 

types  of  lingual  papillae:  filiform  (conical)  (234);  fungiform  (235); 
circumvallate  (vallate)  (236);  and  foliate  (237).  Note  the  taste-buds 
in  the  latter  two  types  of  papillas. 

(3)  Study  an  injected  specimen  of  cat's  tongue  and  note  the  blood 
supply  of  the  muscle,  and  of  the  several  papillae. 

(4)  Study  a  transverse  section  of  the  foliate  papilla  of  the  rabbit's 
tongue.    Note  the  numerous  taste  buds. 

(D)  THE  PALATE  (Palatinum). 

(1)  Study  a  stained  longitudinal  section  of  the  palate  (including 
the  uvula,  the  soft  palate,  and  a  portion  of  the  hard  palate),  noting  the 
character  of  the  epithelium  on  the  nasal  and  oral  surfaces.  Sketch 
(238). 

(E)  THE  PHARYNX. 

(1)  Study  l.p.  a  stained  section  of  the  oropharynx.  Note:  a,  type 
of  epithelium  of  the  mucosa;  b,  character  of  the  tunica  .propria;  c, 
lymphoid  tissue;  d,  boundary  of  fibre-elastic  tissue,  the  representative 
of  both  the  tela  submucosa  and  the  muscularis  mucosa  of  other  portions 
of  the  digestive  tube  (the  elastic  fibers  are  mostly  longitudinally  dis- 
posed) ;  and  e,  the  outermost  layer  of  obliquely  disposed  striped  muscle 
fibers,  among  the  connective  tissue  of  which  are  embedded  many  tubo- 
acinar  mucous  glands.  Sketch  (239). 

(F)  THE  ESOPHAGUS  (Gullet). 

(1)  Study  l.p.  a  stained  transverse  section  through  the  lower  third 
of  the  esophagus.  Note  the  four  tunics  from  within  outward :  a,  tunica 
mucosa;  b,  tela  submucosa;  c,  tunica  muscularis;  and  d,  tunica  adven- 
titia  (fibrosa).  In  the  tunica  mucosa,  note  the  type  of  the  epithelium, 
the  character  of  the  corium  (lamina  propria  mucosae),  and  the  lamina 
muscularis  mucosse.  (Near  the  cardiac  orifice  the  muscularis  mucosae 
consists  of  an  incomplete  inner  layer  of  circularly  disposed  smooth  mus- 
cle cells,  and  a  more  extensive  outer  stratum  of  longitudinally  arranged 
cells;  elsewhere  in  the  esophagus  generally  the  latter  stratum  only 
occurs;  below  the  esophagus  both  layers  occur.)  In  the  tela  submucosa 
note  the  character  of  the  tissue  and  the  mucous  glands.  Do  the  glandu- 
lar alveoli  contain  demilunes?  (Mucus-secreting  glands  are  absent  in 
the  esophagus  of  the  cat,  very  abundant  in  that  of  the  dog,  and  very 
variable  in  man.  They  are  generally  more  abundant  towards  the  oral 
end.)  In  the  tunica  muscularis,  note  the  two  strata  of  smooth  muscle 
cells,  the  outer  longitudinal  and  the  inner  circular  (at  the  cardiac  orifice 


798  DIRECTIONS  FOB  LABORATORY  WORK 

an  additional  innermost  oblique  layer  may  appear).  Is  a  mesothelial 
layer  present  in  the  tunica  adventitia?  Sketch  l.p.  (240)  a  narrow  seg- 
ment through  the  complete  wall. 

(2)  Compare  the  above  section  with  sections  through  the  middle  and 
upper  third  of  the  esophagus.    What  differences  obtain  at  these  levels 
in  the  several  tunics? 

(3)  Compare  a  section  through  the  upper  third  of  the  esophagus 
with  one  through  the  pharynx.     (A  longitudinal  section  through  the 
area  of  transition  from  pharynx  to  esophagus  is  preferable.)      What 
takes  the  place  in  the  pharynx  of  the  muscularis  mucosse  of  the  esoph- 
agus?   Note  that  in  the  upper  end  of  the  esophagus  a  third  innermost 
stratum  of  oblique  or  longitudinal  striped  muscle  fibers  may  occur  in 
the  tunica  muscularis. 

(4)  Study  sections  through  the  upper  cardiac  glands    (superficial 
esophageal  glands).     Sketch  (241). 

(5)  Sketch  small  portions  of  the  my  enteric    (242),  and  the  sub- 
mucous  nerve  plexuses  (243). 

(G)     THE  STOMACH  (V entriculus ;  Gaster}. 

(1)  Study  l.p.  a  stained  longitudinal  section  through  the  area  of 
transition  from  the  esophagus  to  the  cardiac  portion  (pars  cardiaca)  of 
the  stomach.    Note  the  tunica  serosa  of  the  cardia.    Make  sketch  (244) 
including  the  four  tunics.     Sketch  h.p.   (245)  a  cardiac  gland. 

(2)  Study  a  section  through  the  pars  fundica  of  the  stomach  (fun- 
dus  ventriculi).     Sketch  l.p.   (246).     Examine  carefully  under  h.p.  a 
gastric  gland  of  this  region  and  note:  a,  mouth;  b,  foveola  (crypt,  pit)  ; 
c,  neck  (cervix) ;  d,  body  (corpus) ;  and  e,  fundus.     Note  the  different 
types  of  epithelium  occurring  in  the  several  regions.    Sketch  h.p.  (247) 
a  complete  gland,  noting  especially  the  chief  and  parietal  cells.     Sketch 
h.p.   (248)   a  transverse  section  through  the  body  of  a  gastric  gland. 
Look  for  a  lenticular  gland'   (solitary  lymph  nodule)   in  the  tunica 
mucosa. 

(3)  From  a    demonstration   slide  prepared  by  the   Golgi  technic 
sketch  h.p.  (249)  a  portion  of  a  longitudinal  section  of  the  secretory 
region  of  the  fundic  gland  to  show  the  main  lumen  and  the  system  of 
inter-  and  intracellular  secretory  canaliculi. 

(4)  S.tudy  a  section  of  the  pars  pylorica  of  the  stomach.     Sketch 
l.p.  (250).    Sketch  h.p.  (251)  a  gastric  gland  of  this  region.    In  what 
features  do  the  pyloric  and  fundic  glands  differ?     How  do  they  differ 
functionally  as  indicated  by  these  features?     Enumerate  four  salient 


DIRECTIONS  FOR  LABORATORY  WORK  799 

differential  characteristics  between  the  pars  fundica  and  the  pars  pylorica 
of  the  stomach. 

(5)  Study  an  injected  specimen  of  cat's  stomach  showing  the  blood 
supply  of  the  several  tunics.     Sketch  (252). 

(6)  Study  demonstration  preparations  (methylene  blue  technic)  of 
cat's  stomach  showing  the  nerve  supply.     Note  especially  the  myenteric 
and  the  submucous  plexuses.     Sketch  (253). 


(H)     THE  SMALL  INTESTINE  (Intestinum 

(1)  Study  l.p.  a  longitudinal  section  through  the  area  of  transition 
from  the  pylorus  to  the  duodenum.     Compare  part  for  part.     In  the 
duodenum  note:  a,  villi;  b,  intestinal  glands   (crypts  of  Lieberkiihn) ; 
c,  duodenal   (Brunner's)    mucous  glands;  and  d,  the  plica  circulares 
(valvulse  conniventes) .     Sketch   (254).     Enumerate  the  chief  criteria 
for  distinguishing  between  the  duodenum    (small  intestine)    and  the 
pyloric  portion  of  the  stomach. 

(2)  Sketch  h.p. :  a,  a  villus  in  transverse  and  longitudinal  sections 
(255);  b,  intestinal  gland  (256).     Identify  a  cell  of  Paneth. 

(3)  Study  l.p.  a  stained  transverse  section  through  the  jejunum  or 
the  ileum.     Sketch  (257)   at  the  level  of  a  Peyers  patch   (agminated 
nodule).    Difference  in  shape  of  villi  in  the  three  segments  of  the  small 
intestine?    Distribution  of  lymphoid  tissue?    Presence  of  glands  in  the 
tela  submucosa? 

(I)     THE  LARGE  INTESTINE  (Intestinum  crassum). 

(1)  Draw  l.p.  (258)  a  portion  of  a  stained  section  of  the  colon, 
including  the  four  tunics.  How  does  it  differ  in  grosser  features  from 
the  small  intestine?  In  the  relative  abundance  of  goblet  cells?  of  sol- 
itary lymph  nodules?  of  granule  cells  of  Paneth?  Note  the  tenia?  coli 
of  the  tunica  muscularis. 

(J)     THE  VERMIFORM  APPENDIX  (Processus  vermiformis). 

(1)  Study  a  transverse  section  of  a  normal  human  appendix.  Note 
the  relative  abundance  of  the  crypts  of  Lieberkiihn  and  the  solitary 
lymph  nodules;  and  the  differences  in  the  lamina  muscularis  mucosae 
and  the  tunica  muscularis,  as  compared  with  the  colon.  Sketch  (259). 

(K)     CAECUM. 

Study  a  longitudinal  section  through  the  area  of  transition  (cwcum) 
from  the  ileum  to  the  ascending  colon.  Note  the  iliocolic  valve.  Note 


800  DIRECTIONS  FOR  LABORATORY  WORK* 

also  in  the  colon  the  haustra,  the  plicae  semilunares  and  the  appendices 
epiploicae.    Sketch  l.p.  (2 GO). 

(L)     RECTUM. 

Sketch  l.p.  (261)  the  area  of  transition  from  the  rectum  to  the  anus 
to  show  the  structural  differences  in  the  several  tunics.  Compare  the 
rectum  with  the  colon.  Enumerate  the  grosser  differential  marks  among 
colon,  appendix  and  rectum.  Note  rectal  valves,  rectal  columns,  and 
anal  valves. 

Study  an  injected  specimen  of  the  small  intestine  of  the  cat.  Sketch 
the  blood  supply  of  a  villus  and  of  a  crypt  of  Lieberkiihn  (262). 


XV.  THE  LARGE  GLANDS  OF  THE  DIGESTIVE  CANAL 

(A)  THE  LARGER  SALIVARY  GLANDS. 

(1)  THE  PAROTID  GLAND.    Study  under  the  low  power  of  the  micro- 
scope a  stained  section  of  the  parotid  gland.     Sketch    (263),   show- 
ing the  division  into  lobes  and  lobules,  and  the  location  of  the  inter- 
lobular  and  intralobular  excretory  ducts.     Note  the  distinction  between 
the  parenchyma  and  the  stroma  or  interstitial  tissue. 

Sketch  h.p.  (264)  an  alveolus  (acinus)  in  connection  with  its  inter- 
calary duct.  Note  the  shape,  manner  of  distribution  within  the  alveolus, 
stage  of  secretion  as  indicated  by  the  cytology,  staining  reaction  and 
relation  to  the  'basket  cells'  of  the  constituent  secretory  cells  of  the 
acinus.  Sketch  h.p.  (265)  also  transverse  sections  of  the  secretory  (sal- 
ivary) and  the  excretory  portions  of  the  intralobular  duct. 

(2)  THE   SUBLINGUAL   GLAND.     Study   a   stained   section   of  the 
chief  sublingual  gland  (of  man,  dog,  cat  or  rabbit).    Sketch  h.p.  (266) 
an  alveolus  with  a  large  demilune  ('crescent'  of  Gianuzzi).    Explain  the 
functional  significance  of  the  difference  in  staining  reaction  between  the 
cells  lining  the  alveolus  and  those  of  the  demilune.     Probable  function 
of  the  demilune  cells?    Chief  difference  in  duct  systems  of  parotid  and 
sublingual  glands? 

(3)  THE    SUBMAXILLARY     GLAND.       Compare    the     submaxillary 
with  the  parotid  and  sublingual  glands.    Enumerate  the  chief  differen- 
tial characteristics  among  these  three  glands.     Sketch  h.p.   (267)   two 
adjacent  alveoli,  one  of  the  mucous  the  other  of  the  serous  type.    From 
an  injected  specimen  of  cat's  submaxillary  gland  sketch  (268)  the  intra- 


DIRECTIONS  FOR  LABORATORY  WORK  80] 

lobular  blood  supply.  Nerve  supply  of  the  salivary  glands?  Note  dif- 
ferences between  the  resting  and  active  (or  stimulated)  gland. 

(B)     THE  PANCREAS. 

(1)  Study  a  stained  section  of  the  pancreas.    Make  l.p.  sketch  (269) 
to  show  the  arrangement  into  lobes  and  lobules,  and  the  location  of  the 
ducts.     Sketch  h.p.   (270)   an  acinus  with  its  intercalary  duct   (inter- 
mediate duct),  and  a  centro-acinal  cell  group.    Note  the  polar  differen- 
tiation of  the  zymogenous  acinar  cells;  and  the  different  staining  reaction 
of  the  zymogenous  and  the  centro-acinal  cells.     Significance?    What  is 
the  relationship  between  the  distal  granular  zone  of  the  zymogenous  cells 
and  their  basal  filar  zone  ?  the  mitochondria  ?  the  'nebenkern'  ?    How  do 
these  structures  vary  according  to  the  phase  of  functional  activity? 

(2)  Sketch  h.p.   (271)   a  pancreatic  islet   (island  of  Langerhans). 
From  a  specially  prepared  demonstration  slide  of  the  pancreas  sketch 
(272)  cells  of  the  A  and  B  types.    Number,  form,  distribution,  staining 
reaction,  and  significance  of  the  islets? 

(3)  Sketch  h.p.  (273)  a  cross-section  of  a  large  interlobular  duct. 
From  an  injected  specimen  of  a  cat's  pancreas  sketch    (274)    the 

blood  supply  of  the  zymogenous  parenchyma  and  of  the  islets.  Signifi- 
cance of  the  relatively  great  vascularity  of  the  islet?  Eelation  of  the 
capillaries  to  the  cords  of  islet  cells?  Enumerate  the  differential  marks 
between  the  pancreas  and  the  parotid  gland. 

(  C  )     THE  LI  VER  ( Hepar) . 

(1)  Study  l.p.  a  stained  section  of  the  liver:  a,  of  pig  or  camel;  b, 
turtle  or  frog;  c,  cat  or  human.    Enumerate  differences.    From  sections 
a  and  c  sketch  l.p.  (275)  a  hepatic  lobule  including  the  capsule  of  Glis- 
son.     From  section  b,  sketch  h.p.    (276)   a  small  extent  of  the  liver 
tubule,  noting  the  definite  structural  polarity  of  the  constituent  cells. 
Functional  significance  of  the  latter  phenomenon?     Similarity  between 
embryonic  mammalian   liver  and   the   adult  reptilian   and   amphibian 
livers  ?    Significance  ?    What  is  the  shape  of  the  liver  lobules  as  revealed 
by  reconstructions?     Difference  between  a  hepatic  lobule  and  a  portal 
lobule  ? 

(2)  Study  h.p.  a  stained  section  of  the  human  or  cat's  liver.    Sketch 
h.p.  (277)  a  small  area,  noting  the  hepatic  cell-cords  (trabecula?),  the 
interstitial    reticulum,    the    capilliform    sinusoids    (intralobular    capil- 
laries), the  relation  of  the  latter  to  the  cell  cords,  and  of  the  stellate 
cells  (of  von  Kupfer)  to  the  endothelial  lining  cells  and  to  the  liver 


602  DIRECTIONS  FOR  LABORATORY  WORK 

cells  proper.  From  a  demonstration  preparation  according  to  the  Golgi 
technic  or  the  Vance  technic,  draw  h.p.  (278)  a  cell  cord  with  its  inter- 
and  intracellular  secretory  canaliculi.  In  a  section  prepared  according 
to  Mallory's  technic  for  connective  tissue,  study  the  character  of  the 
inter-  and  intralobular  connective  tissue. 

(3)  Sketch  h.p.  (279)  several  types  of  liver  cells:  a,  granular  (with 
zymogenic  and  glycogenic  granules)  ;  b,  fatty;  c,  pigmented;  d,  binu- 
cleated.     Consider  the  questions  regarding  the  presence,  character,  sig- 
nificance and  relation  to  the  bile  capillary  (ductule)  and  to  the  capillary 
blood  supply  (in  health  and  in  disease,  e.g.,  in  jaundice)  of  the  intra- 
cellular bile  canaliculi. 

(4)  Sketch  h.p.    (280)    a  portal  canal    (interlobular  vein,  artery, 
lymphatic  and  bile  duct)  ;  a  central  (intralobular)  vein  (281) ;  a  sub- 
lobular  vein  (282).     Sketch  h.p.  (283)  the  area  of  transition  from  an 
intralobular  to  the  interlobular  bile  duct. 

(5)  From  an  injected  specimen  of  the  cat's  liver  sketch   (284)    a 
small  area  of  the  parenchyma.     Trace  the  path  of  the  portal  and  the 
hepatic  blood  through  the  liver.     Diagram  (285). 

(D)     THE  GALL  BLADDER  (Vesica  fellca). 

(1)  Make  h.p.  sketch  (286)  through  the  wall  of  gall-bladder,  noting 
the  constituents  of  the  several  tunics. 

XVT.    THE  URINARY  SYSTEM 

(A)     THE  KIDNEY   (Ren). 

(1)  From  a  gross  specimen  of  an  adult  human  kidney  divided  in  the 
median  longitudinal  plane,  make  a  sketch   (287)  to  show  the  general 
topography.     Note:   capsule    (tunica   fibrosa,   tunica   adiposa) ;   cortex 
(pars  radiata,  pars  convoluta) ;  medulla  (renal  pyramids,  renal  columns, 
renal  papillae) ;  renal  sinus  (in  hilus),  containing  the  renal  pelvis  (with 
infundibula  or  major  calyces  and  the  minor  calyces).     Note  also  the 
ureter,  and  the  distribution  of  the  branches  of  the  renal  artery  and  vein 
in  relation  to  this  duct. 

(2)  Study  l.p.  a  stained  longitudinal  section  of  the  kidney  of  the 
mouse  or  rat   (or  other  small  mammal).     Sketch   (288).     In  capsule 
note :  mesothelium ;  tunica  albuginea ;  smooth  muscle  ?     Define  a  renal 
lobule  (renculus).    How  does  the  adult  human  kidney  differ  from  that 
of  the  fetus  and  the  infant?  from  that  of  reptiles?  from  that  of  mouse 
and  cat?  from  that  of  horse?  from  that  of  pig? 


DIRECTIONS  FOB  LABORATORY  WORK  803 

(3)  Study  a  stained  longitudinal  (sagittal)  or  radial  section  of  the 
mammalian  kidney.     Make  l.p.  sketch   (289)    (diagrammatic)   to  show 
the   finer  topographic   relationship   of  the   several   divisions   and  their 
larger  constituents.     Note  cortex  corticis,  pars  radiata,  pars  convoluta, 
renal  corpuscle,  renal  column,  and  boundary  and  papillary  zones  of  the 
medulla. 

Sketch  h.p.  (290)  a  renal  corpuscle.  Note:  glomerulus;  capsule 
(visceral  and  parietal  layers)  ;  arterial  pole  (with  afferent  and  efferent 
arterioles)  ;  uriniferous  pole  (neck). 

Sketch  h.p.  (291)  portions  of  the  several  segments  of  a  renal  (urinif- 
erous) tubule:  proximal  convoluted  tubule;  descending  limb  of  Henle's 
loop;  ascending  limb  of  Henle's  loop;  distal  convoluted  tubule;  arched 
collecting  tubule;  straight  collecting  tubule;  papillary  duct. 

Note  the  difference  in  staining  reaction  of  the  two  portions  of  the 
tubule,  divided  at  the  point  where  the  distal  convoluted  joins  the  arched 
collecting  tubule.  Significance  with  respect  of  function?  of  origin? 

(4)  From  a  demonstration  slide  prepared  according  to  Huber's  tech- 
nic  for  isolating  the  renal  tubules  (Anat.  Eec.,  vol.  5,  1911),  sketch  a 
complete  tubule  (292). 

(5)  Study  a  stained   coronal    (tangential)    section   of  the  kidney 
through  cortex.     Identify  the  several  constituents  of  the  pars  radiata 
and  the  pars  convoluta.     Make  a  similar  study  of  a  similar  section 
through  the  medulla. 

(6)  Study  a  longitudinal  section  of  the  kidney  stained  with  Mai- 
lory's  connective  tissue  stain.     Note  the  types  and  distribution  of  the 
connective  tissue. 

(7)  From  a  demonstration  slide  of  the  kidney  prepared  by  Meve's 
mitochondrial  technic,  sketch   (293)  a  portion  of  the  proximal  convo- 
luted tubule.     Shape  of  the  mitochondria?    Function? 

(8)  Study  a  radial  section  of  an  injected  cat's  kidney.  Sketch  (294) 
the  blood  supply.     Note  interlobar  arteries  and  veins;  arciform   (arcu- 
ate)  vessels;  interlobular  vessels;  afferent  and  efferent  glomerular  ar- 
terioles; the  glomerular  rete  mirabile;  the  capillary  supply  of  the  con- 
voluted tubules;  the  stellate  veins;  the  arteriolas  and  venula3  recta?  (verae 
and  spuriae)  of  the  medulla. 

(B)     THE  URINARY  BLADDER  (Vesica  uriwria).         » 

Study  l.p.  a  stained  section  of  the  urinary  bladder.  Make  l.p.  sketch 
(295)  of  segment  of  complete  wall;  h.p.  sketch  (296)  of  tunica  mucosa. 
How  does  the  mucosa  vary  with  the  degree  of  distension  ?  How  does  the 


804  DIRECTIONS  FOR  LABORATORY  WORK 

tunica  muscularis  differ  from  that  of  the  digestive  tube?     Character, 
origin  and  relationship  of  the  trigonum  vesicae? 

(C)  THE  URETER. 

Make  similar  study  and  sketches   (297,  298)   of  ureter  cut  trans- 
versely. 

(D)  THE  URETHRA. 

Make  similar  study  and  sketches  (299,  300)  of  female  urethra.    (The 
male  urethra  should  be  studied  in  connection  with  the  penis.) 

XVII.  THE  MALE  ORGANS  OF  REPRODUCTION 

(Male  Genital  Apparatus) 

(A)     THE  TESTIS  (Orchis). 

(1)  Study  a  gross  fresh  specimen  of  a  mammalian  testis,  with  its 
associated  duct  system.    Identify:  a,  globus  major  (caput),  globus  minor 
(cauda)  and  corpus  of  epididymis;  b,  ductuli  efferentes  (and  coni  vas- 
culosi) ;  c,  ductuli  abberentes   (superior  and  inferior) ;  d,  ductus  def- 
erens;  e,  paradidymis;  and  f,  the  appendices  testis  and  epididymis. 
Sketch  (301). 

(2)  Study  with  hand  lens  a  median  longitudinal  section  of  a  mam- 
malian testis.     Identify:  a,  capsule;  b,  hilus;  c,  mediastinum  (corpus 
Highmori)  with  rete  testis;  d,  lobular  compartments  (lobules  of  testis)  ; 
e,  semniferous  tubules   (tubuli  contorti) ;  and  f,  tubuli  recti.     Sketch 
(302). 

(3)  Study  under  h.p.  a  stained  section  of  an  active  mammalian  testis 
(e.g.,  mouse,  guinea-pig,  human).     Sketch   (303)   a  segment   (or  seg- 
ments) of  the  wall  showing  besides  the  several  phases  of  Spermogenesis 
(viz.:  a,  spermogonium ;  b,  primary  and  c,  secondary  spermocytes — both 
resting  and  in  mitosis — d,  spermatids  in  several  stages  of  metamorphosis 
into  e,  spermium  or  spermozoon),  a  Sertoli  cell   (sustentacular  cell  or 
trophocyte)  with  attached  spermia,  forming  a  'spermoblast'.    Note  also: 
a,  tunica  vaginalis;  b,  tunica  albuginea;  c,  tunica  vasculosa;  and  d, 
inter  lobular  septa.    Sketch  h.p.  (304)  a  portion  of  wall  of :  a,  a  tubulus 
rectus;  and  b,  (305)  the  rete  testis.    What  is  the  form  of  a  seminiferous 
tubule  ?    Its  relation  to  the  lobule  of  the  testis  ?    How  may  the  testis  be 
classified  among  glands? 

(4)  Study  h.p.  a  section  of  the  active  testis  of  a  grasshopper.    Iden- 
tify the   successive   stages   in   spermogenesis.     Count  the  number  of 


DIRECTIONS  FOR  LABORATORY  WORK  805 

chromosomes  in  the  metaphase  plates  of :  a,  the  dividing  spermogonium ; 
b,  the  primary  spermocyte ;  c,  the  secondary  spermocyte.  Note  the  acces- 
sory or  sex  chromosome.  What  is  its  position  and  behavior  in:  a,  the 
resting  primary  spermocyte;  b,  the  dividing  primary  spermocyte;  d,  the 
resting  and  dividing  secondary  spermocytes ;  d,  the  spermatid  ?  What  is 
its  probable  significance  with  respect  of  sex  determination?  sex  control? 
How  do  the  maturation  mitoses  differ  from  ordinary  somatic  cell  di- 
vision? Significance  of  this  difference  from  the  standpoint  of  inher- 
itance? Probable  significance  of  the  chromosomes? 

(5)  THE  SPERMATOZOON  (spermozoon;  spermium;  sperm).    Sketch 
(306)   from  a  stained  section  under  the  oil  immersion  lens  a  human 
spermatozoon.     Compare  with  a  cover-glass  preparation  of  preserved 
sperm.     Identify:  a,  head  (with  perforatorium,  consisting  of  acrosome 
and  galea  capitis)  ;  b,  neck;  c,  middle  piece  or  body  (with  distal  cen- 
trosome,  end  ring,  central  filament  and  spiral  filament) ;  d,  tail;  and  e, 
terminal  filament. 

Compare  with  spermium  of  dog  and  mouse,  and  some  other  mammal 
(e.g.,  opossum). 

From  what  constituents  of  the  spermatid  are  the  several  above- 
enumerated  portions  of  the  fully  developed  spermium  derived? 

Origin,  function  and  fate  (in  fertilization)  of:  a,  the  head;  b,  the 
middle  piece  (with  its  centrosome  and  imtochondrial  spiral  filament) ; 
and  c,  the  tail? 

(6)  THE  INTERSTITIAL  CELLS  (of  Leydig).    Identify  among  the  in- 
tertubular  connective  tissue    (testicular  stroma)    the  interstitial  cells. 
Sketch  (307)   several  adjacent  cells.     Origin,  structure,  probable  func- 
tion and  fate?     Condition  of  the  interstitial  cells,  and  of  the  seminal 
epithelium,  in  cryptorchism  ? 

(B)  THE  DUCT  SYSTEM  OF  THE  TESTIS. 

(1)  TUBULI  EECTI.     Sketch   (308)   h.p.  a  segment  of  the  wall  of 
a  tubulus  rectus  at  the  point  of  transition  to  the  tubulus  contortus. 
With  what  cells  of  the  latter  tubule  are  the  lining  cells  of  the  tubulus 
rectus  homologous? 

(2)  RETE  TESTIS.     Study  l.p.  the  mediastinum  of  the  testis  with 
its  included  rete  tubules.    Sketch  (309)  a  small  area.    Make  h.p.  sketch 
(310)  of  the  lining  epithelium. 

(3)  DUCTULI  EFFERENTES.     Study  l.p.  a  stained  section  through 
the    efferent    ductules    of    the    epididymis.      Sketch     (311)     a    small 
area.    Relation  of  the  ductuli  efferentes  to  the  coni  vasculosi  and  to  the 


806  DIBECTIONS  FOE  LABORATORY  WORK 

globus  major  (caput  epididymis).  Make  h.p.  sketch  (312)  of  a  segment 
of  the  wall,  showing  the  character  of  the  epithelium  (with  its  groups  of 
ciliated  and  non-ciliated  columnar  cells),  the  basement  membrane,  and 
the  muscular  tunica  propria. 

(4)  THE  EPIDIDYMIS.     Make  l.p.  sketch   (313)    of  a  stained  sec- 
tion of  this  extremely  convoluted  duct;  and  a  h.p.  sketch   (314)  of  a 
segment  of  the  wall,  noting  the  character  of  the  epithelium,  the  base- 
ment membrane,  and  the  muscular  tunica  propria.     How  can  the  duct 
of  the  corpus  epididymis  be  distinguished  in  section  from  the  ductuli 
efferentes  of  the  caput  epididymis? 

(5)  THE  DUCTUS  DEFERENS  (Vas  deferens}.    Study  l.p.  a  stained 
section  of  the  ductus  deferens.    Note  the  tunica  mucosa,  the  lamina  pro- 
pria mucosa?  and  the  tunica  muscularis.     Sketch    (315).     Make  h.p. 
sketch    (316)    through  the  mucosa.     How  does   the   epithelial  lining 
differ  in  the  upper,  middle  and  lower  portions?     How  does  the  tunica 
muscularis  of  the  lower  portion  differ  from  that  of  the  remainder  of  the 
duct?    Difference  between  tunica  mucosa  and  tunica  muscularis  of  the 
ureter  and  the  ductus  deferens? 

(6)  THE  SEMINAL  VESICLES.     Sketch  l.p.  (317)  a  segment  of  the 
entire  wall;  and  h.p.  (318)  a  small  extent  of  the  mucosa. 

(7)  THE  EJACULATORY  DUCTS.    Sketch  l.p.  (319)  a  segment  of  the 
complete  wall;  and  h.p.  (320)  a  portion  of  the  mucosa. 

(C)  THE  SPERMATIC  CORD. 

Study  l.p.  a  stained  transverse  section  of  the  spermatic  cord.  Note 
the  following  constituents:  a,  fibrous  stroma;  b,  ductus  deferens;  c,  ex- 
ternal cremaster  (striped)  muscle;  d,  internal  cremaster  (smooth)  mus- 
cle; e,  spermatic  artery  and  veins,  including  f,  the  pampiniform  plexus. 
Sketch  (321). 

(D)  THE  SCROTUM. 

Study  l.p.  a  stained  section  of  the  wall  of  the  scrotum.  Note  rela- 
tively abundant  pigmented  cells  in  stratum  germinativum  of  epidermis; 
loose  corium  (derma)  with  a  considerable  number  of  elastic  fibers  and 
smooth  muscle  cells  (constituting  the  dartos).  In  what  respects  does 
the  skin  of  the  scrotum  differ  from  ordinary  integument?  Sketch  (322). 

(E)  THE  GLANDS  ASSOCIATED  WITH  THE  MALE  GENITAL 

SYSTEM. 

(1)  THE  PROSTATE  GLAND.  Study  l.p.  a  stained  section  of  the 
human  prostate.  Sketch  (323)  a  small  area  showing  several  alveoli 


DIRECTIONS  FOR  LABORATORY  WORK  807 

and  the  abundant  fibre-muscular  stroma.  Contents  of  the  alveoli  ? 
Make  h.p.  sketch  (324)  of  a  small  extent  of  the  mucosa.  Significance 
of  the  alveolar  content? 

(2)  THE  BULBO-URETHRAL  GLANDS  (Cowper's  glands}.  Make  h.p. 
sketch  (325)  of  several  adjacent  alveoli  and  included  fibro-muscular 
stroma.  Character  of  the  muscle  content?  Sketch  h.p.  (326)  a  portion 
of  the  alveolar  lining. 

(F)     THE  PENIS  (Phallus). 

(1)  Study  a  stained  transverse  section  of  the  human  penis,  through 
its  middle  portion.  Note:  a,  corpus  spongiosum  (corpus  cavernosum 
uretlme)  with  the  urethra;  b,  urethral  glands  (glands  of  Littre) ;  c,  the 
two  corpora  cavernosa  (penis)  ;  d,  the  enveloping  tunica  albuginea,  and 
c,  the  peripheral  cutaneous  envelope.  Sketch  (327).  Sketch  h.p.:  a, 
the  lining  of  the  urethra  including  a  urethral  gland  (328)  ;  b,  a  small 
area  of  erectile  tissue  from  one  of  the  corpora  (329) ;  and  e,  a  helicine 
artery  (330).  How  does  the  epithelium  of  the  urethra  differ  in  its  sev- 
eral segments,  namely  the  prostatic,  the  membraneous,  the  penile,  and 
the  glans  (fossa  navicularis)  portions? 

Sketch  l.p.  (331)  portion  of  a  preputial  gland  from  a  section  through 
the  corona.  Location  and  significance  of  Tyson's  glands?  Note  char- 
acter of  the  skin  of  the  glans  penis. 

Trace  the  course  of  the  blood  through  the  penis  in  the  flaccid,  and 
in  the  erect  condition.  Nerve  supply  and  nerve  end-organs? 

XVIII.    THE  FEMALE  ORGANS  OF  REPRODUCTION 

(Female  Genital  System) 

( A )     THE  OVARY  ( Ovarium ) . 

(1)  Study  l.p.  and  h.p.  a  stained  section  of  the  ovary  of  a  full-term 
fetus  or  young  infant.     Note :  a,  the  peripheral  'germinal  epithelium', 
with  its  larger  spherical  primordial  germ  cells  (ova) ;  b,  egg  tubes  of 
Pflueger :  c,  'egg  nests' ;  and  d,  a  typical  primitive  ovarian  follicle  with 
its  central  ovum    (primary  ob'cyte)    and  its  enveloping  mantle  layer. 
Sketch  each  under  the  h.p.   (332  a,  b,  c  and  d).     Derivation  of  the 
ovarian  germ  cells? 

(2)  Study  l.p.  a  stained  section  of  the  ovary  of  an  adult.    Note:  a, 
the  enveloping  peritoneal  layer  ('germinal  epithelium')  ;  b,  the  periph- 
eral cortex  with  its  ovarian  follicles  and  the  superficial  tunica  albuginea; 


808  DIRECTIONS  FOE  LABOEATORY  WORK 

and  c,  the  medulla,  coming  to  the  surface  at  the  hilus.  Sketch  (333). 
In  the  cortex  note  also  the  corpora  lutea  and  the  corpora  albicantia. 
What  is  their  significance?  Make  h.p.  sketches  (334,  335)  of  portions 
of  each.  Make  h.p.  sketch  (336)  of  a  typical  area  of  the  medulla. 

Sketch  h.p.  also:  a,  a  primary  ovarian  follicle  (337)  ;  b,  a  follicle  at 
an  intermediate  stage  of  growth  (338)  ;  and  c,  an  older  vesicular  (Graaf- 
ian)  follicle  (339),  noting  all  the  constituent  elements.  Manner  of 
derivation  of  the  secondary  oocyte  from  the  primary  oocyte  of  the  ves- 
icular follicle?  ootid  from  secondary  oocyte? 

(3)  Study  an  injected  specimen  of  a  cat's  ovary.    What  is  remark- 
able about  the  arteries?    Sketch  (340)  an  area  of  the  medulla,  and  an 
adjacent  vesicular  follicle. 

(4)  Oogenesis.     Sketch  the  several  salient  stages  of  oogenesis  from 
a  series  of  demonstration  slides  of  eggs  of  mouse  or  starfish :  a,  unripe 
(small)    ovarian   egg    (primary  oocyte)    (314) ;  b,  ripe    (full-grown) 
primary  oocyte  (342)  ;  c,  first  maturation  spindle  (343)  ;  d,  secondary 
oocyte  with  first  polocyte  (344) ;  e,  second  maturation  spindle  (345) ; 
f,  ootid  or  mature  ovum  with  second  polocyte  (346). 

(B)  THE  UTERINE  TUBE  (Oviduct;  Fallopian  tube;  Salpinx). 
Make  a  comparative  study  of  transverse  sections  of  the  uterine  tube 

at:  a,  the  isthmus;  b,  the  ampulla;  c,  the  infundibulum,  noting  differ- 
ences in  the  size  of  the  lumen,  and  the  character  and  constituents  of  the 
three  tunics  (tunica?  mucosa,  muscularis  and  serosa).  Diagram  (347). 
Sketch  h.p.  (348)  a  segment  of  the  mucosa  from  the  isthmic  region. 
Differential  features  among  uterine  tube,  ductus  def erens  and  the  ureter  ? 

(C)  THE  UTERUS  (Metra;  Hystera). 

Compare  vertical  sections  through  the  body  and  cervix  of  the  uterus. 
Sketch  l.p.  (349)  a  narrow  segment  of  the  entire  wall  from  both  regions. 
Enumerate  the  chief  differences.  Sketch  h.p. :  a,  the  mucosa  of  the  body 
(350);  b,  a  cervical  gland  (351).  Significance  of  non-ciliated  areas? 
How  many  strata  in  the  tunica  muscularis  ?  Which  is  the  stratum  vas- 
culare?  How  does  the  resting  uterus  differ  from  the  menstruating 
uterus?  from  the  pregnant  uterus?  How  does  the  human  uterus  differ 
in  gross  form  and  with  respect  of  the  muscular  tunic  from  that  of  cer- 
tain common  mammals,  e.g.,  dog,  cat,  etc.? 

(D)  THE  VAGINA. 

Study  l.p.  a  section  from  the  middle  portion  of  the  vagina.  Note: 
a,  the  tunica  mucosa;  b,  tunica  muscularis;  c,  tunica  fibrosa.  Sketch 


DIRECTIONS  FOE  LABORATORY  WORK  809 

(352).  Type  of  lining  epithelium?  Are  glands  present?  What  is  the 
striking  common  characteristic  of  the  tunica  propria  of  the  entire  duct 
system  of  the  female  genital  apparatus? 

(E)  THE  EXTERNAL  GENITALS. 

These  include:  a,  the  vestibule;  b,  the  labia  minora;  c,  the  labia 
majora ;  d,  the  clitoris ;  e,  the  hymen ;  f ,  the  minor  vestibular  glands,  and 
g,  the  major  vestibular  glands.  Enumerate  the  histologic  characteristics 
of  each.  What  are  the  male  homologues  for  d,  f,  and  g?  The  major 
vestibular  glands  (glands  of  Bartholin)  open  into  the  groove  between 
the  hymen  and  the  labium  minus.  Sketch  h.p.  several  adjacent  alveoli 
of  this  gland  (353). 

(F)  THE  MAMMARY  GLAND  (Mamma). 

(1)  Study  l.p.  a  section  of  the  active  (lactating)  gland.    Note  the 
arrangement  into  lobes  and  lobules.     Sketch  (354),  showing  the  inter- 
lobar  lactiferous  duct  and  the  inter-  and  intralobular  ducts.    Make  h.p. 
sketch  (355)  of  an  alveolus,  noting  especially  the  cytoplasmic  contents 
of  the  lining  cells.     Significance  of  the  basket  cells?  of  the  basal  stria- 
tions  of  the  secretory  cells? 

(2)  Make  l.p.  study  of  a  resting  mammary  gland.     Sketch  (356). 

(3)  Examine  a  cover-glass  preparation  of  fresh  milk  stained  with 
methylene  blue.    Note  especially  the  leucocytes  and  fat  droplets.    Sketch 
(357).     Derivation  of  the  leucocytes? 

(4)  Enumerate  the  histologic  features  of:  a,  the  mammilla;  b,  the 
areola ;  c,  the  glands  of  Montgomery,  and  d,  the  integument  of  the 
mammae.     Character  and  significance  of  'witches  milk'? 

XIX.    DUCTLESS  GLANDS 

(Endocrine  Glands;  Organs  of  Internal  Secretion;  Cryptorhetic  Glands) 

(A)     THE  SUPRARENAL  GLANDS  (Adrenals). 

(1)  Examine  a  divided  fresh  suprarenal  gland  of  some  mammal. 
Note  the  yellowish  coloration  of  the  cortex,  and  the  red  color  of  the 
medulla;  note  also  the  capsule  and  the  hilus.     Cause  of  difference  in 
color  between  cortex  and  medulla? 

(2)  Study  l.p.  stained  vertical  sections  of  the  human  and  the  dog's 
adrenal.    Chief  differences?    Sketch  (358)  a  narrow  segment  from  cap- 
sule to  center  of  medulla.     Make  h.p.  sketches  (359)  of  groups  of  cells 


810  DIRECTIONS  FOR  LABORATORY  WORK 

from  the  zonae  glomerulosa,  fasciculata  and  reticularis.  Enumerate  the 
chief  differences  in  gross  arrangement  of  the  cells  and  in  their  cyto- 
plasmic  contents.  Sketch  also  (360)  a  group  of  cells  from  the  medulla. 
What  is  the  chief  granular  content  of  these  cells  ?  Significance  ?  Sketch 
also  (361)  a  segment  of  the  central  vein.  What  is  remarkable  about  this 


(3)  Study  a  stained  horizontal  section  through  the  zona  glomerulosa. 
Arrangement  of  the  glomerular  cells?    Function  of  the  adrenal?    Rep- 
tilian and  ichthyoid  homologues? 

(4)  Study  an  injected  specimen  of  cat's  adrenal.    Diagram  the  ar- 
terial blood  system  (362).     Relation  of  the  cells  to  the  venous  capil- 
laries ?    Significance  of  the  separate  blood  supply  of  the  cortex  and  the 
medulla? 

(B)  THE  THYROID  GLAND. 

Study  l.p.  a  stained  section  of  the  human  thyroid  gland.  Note :  cap- 
sule, lobules,  follicles  and  colloid  content  of  latter.  Sketch  (363)  a 
small  area  including  the  capsule  and  the  interfollicular  stroma.  Sketch 
h.p.  (364)  a  folicle,  noting  especially  the  two  types  of  lining  cells:  a, 
chief  cells;  b,  colloid  cells.  What  are  the  striking  characteristics  of  the 
colloid  content  of  the  follicle?  Cellular  inclusions  in  the  colloid? 

From  an  injected  specimen  of  the  cat's  thyroid  diagram  the  blood 
supply  of  a  lobule  (365). 

What  morbid  condition  is  associated  with  atrophy  of  the  thyroid? 
with  hypertrophy  (hypersecretion)  ?  with  arrested  development?  Nor- 
mal function? 

How  does  aberrant  or  accessory  thyroid  tissue  differ  from  that  of 
the  thyroid  proper? 

What  are  the  salient  differential  characteristics  of  sections  of  the 
thyroid,  active  mammary  gland  and  prostate  gland? 

(C)  THE  PARATHYROID  GLANDS. 

Make  h.p.  sketch  (366)  of  a  small  area  of  a  stained  section  of  a 
parathyroid  (epithelial  body).  Note  the  'acidophiP  and  'principal'  types 
of  cells.  Does  colloid  material  occur?  Spatial  and  functional  relation- 
ship between  thyroid  and  parathyroids.  Function  of  the  parathyroids? 

(D)  THE  THYMUS  GLAND. 

Study  l.p.  a  stained  section  of  the  human  thymus.  Note:  capsule, 
lobules  (with  cortex  and  medulla)  and  interlobular  connective  tissue 


DIRECTIONS  FOB  LABORATORY  WORK  •         811 

septa.  Sketch  (367)  several  adjacent  lobules.  Note  continuity  of 
medullary  substance  between  adjacent  lobules.  Make  h.p.  sketch  of  a 
lobule  (3G8)  ;  also  of  a  thymic  corpuscle  (concentric  corpuscle  of  Has- 
sall)  (369).  Where  are  the  latter  located  ?  Origin  and  function  of  the 
thymic  corpuscles?  Is  the  thymus  a  lymphoid  organ  or  an  endocrin 
(cryptorhetic)  gland?  Ontogenetic  history  of  the  thymus?  From  an 
injected  specimen  of  cat's  thymus,  sketch  (370)  the  blood  supply  of  a 
lobule. 

(E)  THE  CAROTID  GLAND. 

Location,  origin  and  probable  function  of  this  gland?  Sketch  h.p. 
(371)  a  small  area.  Compare  with  the  Coccygeal  Gland  and  the  Para- 
ganglia.  Origin  and  function  of  the  latter? 

(F)  THE  HYPOPHYSIS  CEEEBRI  (Pituitary  Gland). 

In  a  stained  sagittal  section  of  the  human  hypophysis  identify:  a, 
pars  neuralis  (posterior  lobe)  ;  b,  pars  juxtaneuralis  (intermediate  por- 
tion) ;  c,  residual  lumen;  d,  pars  distalis  (anterior  lobe).  Make  h.p. 
sketches  (372)  of  a  small  area  from  each  of  these  portions.  In  the  pars 
distalis  note  the  cords  of  central  neutrophilic  and  parietal  eosinophilic 
cells.  Significance  of  these  two  types?  Over  the  periphery  of  the  pars 
distalis  and  lining  the  residual  lumen  note  the  basophilic  cells.  Signifi- 
cance? What  are  the  'chromophobe'  cells? 

Origin  and  probable  function  (normal  and  morbid)  of  this  gland? 
Blood  and  nerve  supply? 

(G)  THE  EPIPHYSIS  CEREBRI  (Pineal  Body). 

Study  l.p.  a  stained  sagittal  section  of  the  adult  sheep's  pineal  body. 
Note :  pineal  stalk  with  its  pineal  recess ;  capsule,  'lobes',  trabeculae,  and 
acervulus  (brain  sand).  Compare  with  the  human  pineal  body.  Sketch 
h.p.  (373)  a  small  area  near  the  periphery.  Note  the  two  chief  types 
of  cells:  rieuroglia  and  'interneurogliar'.  Significance  of  the  two  types? 
Note  also  the  intercellular  clumps  of  pigment,  and  the  lamellated  and 
conglomerate  types  of  acervulus,  and  the  larger  edematous  areas.  Com- 
pare with  a  similar  section  of  this  gland  from  a  young  sheep.  In  the 
latter  note  the  intracellular  pigment  granules  and  the  intercellular  cysts. 
Origin  and  probable  function  (normal  and  morbid)  of  this  gland? 
Blood  and  nerve  supply?  Significance  of  the  melanic  pigment?  of  the 
cysts?  of  the  brain  sand? 


812  BISECTIONS  FOE  LABOEATORY  WOEK 

XX.    THE  EYE 

(Bulbus  Oculi,  and  Appendages:  Palpebrce  and  Lacrimal  Glands) 

(A)     MACROSCOPIC  STUDY. 

(1)  With  the  aid  of  a  mirror,  sketch  your  eye   (374).     Note:  a, 
supercilium   (eye-brow)  ;  b,  superior  and  inferior  palpebra?   (eye-lids), 
with  their  cilia  (eye-lashes)  at  the  base  of  which  internally  may  be  seen 
a  row  of  whitish  pits,  the  orifices  of  the  tarsal  (Meibomian)  glands;  c, 
the  medial  and  lateral  anguli  oculi  and  the  canthi  (commissures) ;  d,  in 
the  depth  of  the  medial  angle  (the  lacus  lacrimalis)  a  reddish  rough- 
ened area,  the  caruncula  lacrimalis ;  e,  at  the  base  of  this  angle  the  plica 
semilunaris    (homologue  of  nictitating  membrane  or  third  eye-lid  of 
birds,  reptiles,  etc.),  and  f,  at  either  basal  angle  of  the  internal  canthus 
an  elevated  papilla  lacrimalis,  with  its  punctum  lacrimalis  leading  to 
the  canaliculus  lacrimalis  and  the  naso-lacrimal  duct.     Note  also  the 
fine  hairs  on  the  caruncula.     Eetract  the  lower  lid  and  note  the  con- 
junctive palpebrae;  its  continuity  with  the  conjunctiva  oculi  across  the 
fornix  conjunctiva?  can  readily  be  observed. 

Within  the  rima  palpebrarum,  the  opening  between  the  lids,  note: 
a,  the  pupil;  b,  the  iris;  and  c,  the  overlying  transparent  cornea,  con- 
tinuous peripherally  with  the  opaque  sclera.  What  is  the  pinguecula? 

(2)  In  a  formalin-preserved  specimen  of  the  eye-ball  of  sheep  or  ox, 
dissect  out  carefully  the  six  extrinsic  eye-muscles.     Note  the  point  and 
manner  of  insertion  of  the  muscles  and  the  relation  of  the  superior  and 
inferior  obliques  to  the  superior  and  inferior  recti  muscles  respectively. 
The  levator  palpebra?  superioris  muscle  may  also  have  remained  intact; 
also  a  muscle  attached  by  a  stout  tendon  to  the  well-developed  carti- 
laginous plica  semilunaris,  the  musculus  plica?.    In  the  eyes  of  ruminants 
an  additional  muscle  occurs,  not  present  in  the  human  eye,  the  retractor 
bulbi ;  this  large  stout  muscle  completely  envelops  the  optic  nerve.    Sep- 
arate the  retractor  bulbi  muscle  from  the  optic  nerve  down  to  the  point 
of  exit  of  the  nerve  from  the  bulb.    By  noting  the  position  of  the  point 
of  exit  with  respect  to  the  posterior  pole  of  the  bulb,  and  the  relation  of 
this  point  to  the  plica  semilunaris  and  levator  palpebrae  muscle,  deter- 
mine which  eye  you  have  been  dissecting.    Sketch  anterior  and  posterior 
poles  (375). 

(3)  Bisect  the  eye-ball  in  the  horizontal  meridian.     (This  should  be 
done  with  a  sharp  razor,  proceeding  from  the  posterior  pole,  first  divid- 


DIRECTIONS  FOR  LABORATORY  WORK  813 

ing  the  optic  nerve.)  Examine  under  water.  Note:  cornea,  iris,  crys- 
talline lens,  suspensory  ligament  (zonula  ciliaris  of  Zinn)  of  lens,  an- 
terior and  posterior  chambers  with  their  content  of  aqueous  humor;  the 
ciliary  body  with  the  ciliary  folds  and  processes;  the  ora  serrata;  the 
vitreous  humor  (body)  ;  the  retina;  the  tunica  choroidea;  the  sclera;  the 
lamina  fusca  and  the  lamina  suprochoroidea  between  the  separated  por- 
tions of  the  choroid  and  sclerotic  coats ;  the  macula  lutea  with  the  fovea 
centralis;  the  optic  papilla  (disc)  with  the  central  depression  (physio- 
logic excavation);  hyaloid  canal;  and  the  hyaloid  membrane.  Sketch 
(376).  Significance  of  the  hyaloid  canal  (canal  of  Cloquet;  canal  of 
Stilling)  ? 

Remove  the  lens.  Note  the  difference  in  curvature  of  its  anterior 
and  posterior  surfaces.  Eemove  the  anterior  lens  epithelium,  and  the 
lens  capsule.  Eemove  the  more  superficial  layer  of  lens  fibers  and  free 
the  central  non-nucleated  lens  'nucleus'.  Explain  the  arrangement  of 
the  lens  fibers,  with  relation  to  each  other,  the  'nucleus',  and  the  poles 
of  the  lens  (lens  'stars').  Sketch  (377). 

How  is  the  lens  held  in  place  ?  Describe  the  action  of  the  lens.  What 
is  a  cataract  of  the  eye?  Difference  between  the  anatomic  axis  of  the 
bulb  and  the  visual  axis?  Embryonic  origin  of  the  several  tunics  and 
humors  of  the  bulbus  oculi,  and  of  the  lens?  What  is  the  capsule  of 
Tenon? 

(B)     MICROSCOPIC  STUDY. 

(1)  Study  l.p.  a  stained  horizontal  section  of  the  human  eyeball  (or 
that  of  cat,  dog  or  monkey).     (The  bulb  should  have  been  preserved  in 
Perenyi's  fluid,*  which  softens  the  lens).     Sketch    (378).     Note  the 
difference  in  curvature  between  the  cornea  and  the  posterior  scleral  seg- 
ment of  the  bulbus  oculi;  also  between  the  anterior  and  posterior  sur- 
faces of  the  lens.     Identify  the  several  chambers,  angles  and  tunics  of 
the  bulb,  and  the  several  laminae  of  each  tunic.    Note  the  disposition  of 
the  nuclei  in  the  lens.    Enumerate  and  identify  the  intrinsic  muscles  of 
the  eye.    Explain  their  nerve  supply.    Explain  the  action  of  the  ciliary 
body.     Function  of  the  aqueous  chambers  and  the  canal  of  Schlemn; 
(sinus  venosus  sclerse)  ?    Eelation  to  glaucoma?    Define  astigmatism. 

(2)  Study  h.p.  the  sclero-corneal  junction.    Identify  all  of  its  con- 

*  Perenyi's  fluid:  4  parts  10  per  cent  nitric  acid 

3  parts  alcohol  (95%) 

3  parts  0.5  per  cent  chromic  acid. 
Fix  5  to  10  hours,  and  pass  directly  into  70%  alcohol. 


814  DIRECTIONS  FOE  LABORATORY  WORK 

stituent  elements,  and  note  its  relationship  to  adjacent  structures. 
Sketch  (379).  Function  of  ligamentum  pectinatum  and  the  included 
spaces  of  Fontana? 

(3)  Sketch  h.p.  (380)  the  cornea.    Identify  its  five  layers.    Inner- 
vation  of  the  corneal  conjunctiva?    Function  of  the  membrane  of  Des 
cemet?     Changes  in  cornea  after  death  or  fixation? 

(4)  Sketch  h.p.   (381)   the  sclera.     Location  and  character  of  the 
lamina  fusca? 

(5)  Sketch  h.p.  (382)  the  tunica  choroidea.    Note  the  several  lam- 
inae: suprachoroidea,  vasculosa,  tapetum  fibrosum  (cellulosum),  chorio- 
capillaris,  and  lamina  basalis  (vitrea).     Function  of  the  choroid? 

(6)  Sketch  h.p.  (383)  the  equatorial  margin  of  the  crystalline  lens, 
including  the  zonula  ciliaris  of  Zinn    (suspensory  ligament)   with  its 
spacia  zonularis   (canals  of  Petit).     Note  the  lens  capsule,  lenticular 
epithelium,  and  the  substantia  lentis  composed  of  nucleated  lens  fibers, 
with  serrated  margins. 

(7)  Sketch  h.p.  (384)  a  segment  of  the  iris.    Note:  a,  its  external 
layer  of  mesenchymal  epithelium  ('endothelium')  ;  b,  its  fibrous  stroma, 
with  its  pigmented  cells;  c,  the  internal  epithelial  layer   (pars  iridica 
retina?);  d,  the  stromal  recesses;  e,  the  dilator  and  sphincter  muscles; 
and  f,  the  circuli  major  and  minor.     Origin  and  function  of  the  iridal 
muscles?     Relation  of  pigmented  stroma  to  'color  of  eye'?     Effect  of 
certain  drugs  upon  the  size  of  the  pupil? 

(8)  Sketch  h.p.  (385)  the  pars  optica  retinae,  or  the  retina  proper, 
at  a  point  about  midway  between  the  macula  lutea  and  the  ora  serrata. 
Relation  to  pars  ciliaris  retina?  and  the  pars  iridica  retina??     Identify 
the  eleven  different  layers.    Compare  this  portion  of  the  retina  with  that 
near  the  fovea  centralis  and  that  near  the  ora  serrata.    Probable  function 
of:  a,  the  pigment  (fuscin)  of  the  pigmented  layer;  b,  the  visual  purple 
(rhodopsin)   of  the  rod  visual  cells;  and  c,  the  myoid  element  of  the 
rods  and  cones  ?    Explain  the  inversion  of  the  retina.    Explain  coloboma 
and  scotoma. 

(9)  In  a  Golgi  preparation  of  the  retina  identify  the  different  neu- 
rons of  the  several  layers  and  determine  their  interrelations  (synapses). 
Construct  a  diagram  (386)   showing  the  interrelationships  of  the  ele- 
ments of  the  different  layers,  including  the  neuroglia  supporting  cells  of 
Miiller. 

(10)  (a)   Study  an  injected  specimen  of  cat's  eye.     Note  the  dis- 
tribution of  the  branches  of  the  central  artery  of  the  retina,  the  short 
ciliary  arteries,  the  long  ciliary  arteries,  and  the  anterior  ciliary  arteries, 


DIRECTIONS  FOE  LABORATORY  WORK  815 

especially  with  respect  to  the  uvea  or  complete  middle  tunic.  Do  these 
several  arterial  systems  anastomose?  Note  also  the  radicles  of  the  vena 
vorticosa?.  Sketch  (387)  lateral  half  of  bulbus  oculi. 

(b)   Trace  out  also  the  lymphatic  systems  of  the  eye. 

(C)     THE  OCULAR  APPENDAGES. 

(1)  THE    PALPEBR^E    (eye-lids}.      Study    l.p.    a    stained    vertical 
section  of  the  human  superior  eye-lid.     Note:  cutaneous  surface,  rimal 
margin  and  the  conjunctival  surface;  the  orbicularis  palpebrarum  mus- 
cle, insertion  of  the  musculus  levator  palpebrae  superioris,  the  superior 
palpebral  muscle  of  Miiller,  the  ciliary  muscle  of  Kiolan,  and  the  tarsal 
fascia  (tarsus) ;  the  cilia  (eye-lashes),  sebaceous  glands  of  Zeiss,  glands 
of  Moll,  tarsal  glands  of  Meibon,  and  the  glands  of  Waldeyer  (posterior 
tarsal  glands)  ;  the  primary  and  secondary  tarsal    (arterial)    arches. 
Sketch  (388). 

Make  h.p.  sketch  (389)  of  the  palpebral  conjunctiva  near  the  level 
of  the  fornix  conjunctivas. 

(2)  THE  LACRIMAL  GLAND.    Study  a  stained  section  of  the  lacrimal 
gland.     Sketch  l.p.   (390)   a  lobule,  showing  the  ducts  and  the  secre- 
tory tubules.    Make  h.p.  sketches  (391,  a,  b,  etc.)  of  sections  of  tubules 
at  several  stages  of  secretory  activity.    Where  are  the  accessory  lacrimal 
glands  of  Krause?    Location  and  significance  of  the  gland  of  Harder? 

XXI.    THE  EAR 

(A)  THE  EXTERNAL  EAR. 

(1)  AURICLE   (Pinna}.     Study  l.p.  a  stained . section  of  the  lobule 
of  the  ear,  including  adjacent  portion  of  the  pinna.     Note  the  absence 
of  cartilage  in  the  lobule  proper,  and   the  abundant  adipose   tissue. 
Sketch  (392).     Make  h.p.  sketch  (393)  of  portion  of  the  elastic  carti- 
lage of  the  pinna.     Note  the  relatively  large  number  of  cells. 

(2)  Study  l.p.  a  stained  section  of  the  cartilaginous  portion  of  the 
External  Acoustic  Meatus.     Note  the  abundant  large  stiff  hairs,  seba- 
ceous glands,  and  ceruminous  glands.    Sketch  (394).    Sketch  h.p.  (395) 
a  transverse  section  of  the  secretory  portion  of  the  coiled,  simple  tubular, 
ceruminous  gland.    Enumerate  differences  and  resemblances  between  the 
ceruminous  glands,  the  sudoriparous  glands,  and  the  mammary  glands. 

(B)  THE  MIDDLE  EAR  (Tympanum). 

(1)   Study  l.p.  a  stained  radial  section  of  the  tympanic  membrane, 
Note:  annulus  tympanicus;  umbo,  with  attached  manubrium  of  the 


816  DIRECTIONS  FOR  LABORATORY  WORK 

malleus;  membrana  flaccida  (Shrapnell's  membrane)?  and  cutaneous 
layer,  mucous  layer,  and  intermediate  radial  and  circular  collagen  fibers. 
Sketch  (396).  Sketch  (397)  h.p.  a  small  segment  of  the  tympanic 
membrane  near  the  umbo.  Function  of  tympanic  membrane  ?  Relation 
to  the  auditory  ossicles?  Structure  of  the  ossicles?  Relation  of  tym- 
panum to  the  mastoid  'cells'?  to  the  auditory  tube? 

(2)  THE  AUDITORY  TUBE  (Eustachian  Tube).  Study  a  stained 
transverse  section  of  the  cartilaginous  portion  of  the  tuba  auditiva. 
Note  character  of  the  lining  epithelium,  and  the  fibro-cartilagiiious 
wall.  Relation  of  cartilage  plate  to  medial  and  lateral  surfaces,  and  to 
the  tensor  and  levator  palati  muscles.  Sketch  (398).  Function  of  the 
auditory  tube  ?  Position  and  significance  of  the  tubal  tonsil  ?  Function 
of  the  musculus  tensor  palati  in  relation  to  the  auditory  tube? 

(C)     THE  INTERNAL  EAR 

(1)  VESTIBULE    (Utriculus  and  Sacculus).     Study  a  stained  sec- 
tion of  the  wall  of  the  utricle  or  saccule  through  the  macula.    Note  char- 
acter of  the  lining  epithelium.     Sketch  h.p.    (399)   a  segment  of  the 
macula.     Function  of  the  otolithic  membrane? 

(2)  SEMICIRCULAR  DUCTS   (Canals).     Study  h.p.  a  stained  trans- 
verse  section   of   a   membraneous   semicircular    duct.      Compare    with 
a  section  through  the  ampulla.     Sketch  segments  of  the  lining  epithe- 
lium (400),  and  of  the  crista  ampulla?  acustica  including  the  overlying 
cupola  (401). 

(3)  COCHLEA.     Study  l.p.  a  stained  axial  section  of  the  cochlea 
of  some  mammal  (cat;  rabbit).     Sketch  a  complete  vertical  section  of 
a  turn  of  the  cochlea  (402).    Identify  and  label  all  the  included  parts. 
Function  of  the  vestibular  (Reissner's)  membrane?  tectorial  membrane? 
basilar  membrane  ?  Shambaugh's  glands  ?  the  stria  vascularis  ?  vas  prom- 
inens  ? 

Make  h.p.  sketch  (403)  of  the  spiral  organ  (of  Corti),  identifying 
the  various  cells  involved. 

Study  an  injected  specimen  of  the  caf  s  cochlea.  Diagram  (404)  the 
blood  supply  of  a  turn  of  the  cochlea. 

Describe  the  nerve  supply  of  the  membraneous  labyrinth,  of  the  in- 
ternal ear.  Where  is  the  internal  acoustic  meatus?  Function  of  the 
utriculus?  sacculus?  semicircular  canals?  cochlea? 


DIRECTIONS  FOR  LABORATORY  WORK  817 


XXII.    THE  NERVOUS  SYSTEM 

(A)     THE  SPINAL  CORD   (Medulla  spinalis). 

(1)  Study  l.p.  a  stained   (preferably  by  the  Weigert-Pal  technic) 
transverse  section  of  the  spinal  cord  in  the  lower  cervical  region,  includ- 
ing a  spinal  ganglion.     Compare  with  the  upper  cervical  and  thoracic 
levels.    Note  the  enveloping  membranes  (spinal  meninges)  :  dura  mater, 
arachnoidea,  and  the  pia  mater;  and  their  continuity  with  the  connective 
tissue  envelopes  of  the  spinal  nerve.     Sketch  (405)  a  segment  through 
these  membranes  with  the  included  lymph  spaces.     Note  the  greater 
vascularity  of  the  pia  mater  spinalis.    Note  further  the  compressed  oval 
shape  of  the  lower  cervical  section,  and  its  division  into  symmetrical 
halves  by  the  dorsal  longitudinal  septum  and  the  ventral  longitudinal 
fissure;  also  the  central  canal;  the  central  gray  matter  arranged  in  the 
form  of  an  H  with  its  dorsal,  ventral,  and  lateral  horns  and  their  con- 
stituent cell  groups ;  the  peripheral  white  substance,  divisible  into  dorsal, 
lateral,  and  ventral  columns;  the  gray  and  white  commissures;  the  sub- 
stantia  gelatinosa  centralis,  and  the  gelatinous  substance  of  Kolandi ;  the 
formatio  reticularis;  the  cell  column  of  Clarke;  nucleus  of  Stilling;  the 
connective  tissue  and  neuroglia  septa  of  the  white  substance;  and  the 
dorsal  and  ventral  roots  of  the  spinal  nerves.     Sketch  (406).    Describe 
the  structural  differences  between  gray,  white,  gelatinous,  and  reticular 
substances.    Compare  the  lower  cervical  with  the  lumbar  and  sacral  sec- 
tions.   Differences?    Development  of  the  spinal  medulla?    Define  tract 
(fasciculus),  column  (funiculus),  and  nucleus  (of  origin  and  termina- 
tion) of  the  spinal  cord.    Define:  conus  medullaris,  filum  terminate,  and 
the  cauda  equina.     Describe  the  relations  to  each  other  of  the  sensory, 
motor  and  association  neurons  in  the  spinal  cord. 

(2)  Study  l.p.  an  injected  specimen  of  the  spinal  cord  of  the  cat. 
Note  the  five  longitudinal  arterial  trunks  in  the  pia  mater  spinalis :  the 
larger  antero-median  artery,  and  the  more  slender  postero-lateral  longi- 
tudinal arterioles   (arranged  anteriorly  and  posteriorly  to  the  line  of 
entrance  of  the  posterior  nerve  roots).     Note  their  further  penetration 
and  distribution  within  the  gray  and  white  substances.     (Sketch  (407). 

Location,  structure  and  function  of  the  septum  posticum,  the  liga- 
menta  denticulata  and  the  subarachnoid  spaces?  origin  of  cerebrospinal 
fluid?  Trace  the  course  of  the  lymph  circulation  through  the  central 
nervous  system. 


818  DIEECTIONS  FOR  LABORATORY  WORK 

(B)     THE  CEREBELLUM. 

(1)  Study  l.p.  a  stained  parasagittal  section  of  a  hemisphere  of  the 
human  cerebellum.     Note  the  arrangement  into  lobules  composed  of 
folia.     Note  also  that  each  folium  comprises  a  central  medulla  and  a 
peripheral  cortex.    In  the  cortex  identify  the  superficial  molecular  layer, 
the  deeper  nuclear  or  granular  layer,  and  between  the  two  the  inter- 
mediate layer  of  Purkinje  cells  (commonly  classified  as  the  innermost 
stratum  of  the  molecular  layer).     Sketch    (408).     Make  h.p.  sketch 
(409)  of  a  Purkinje  cell. 

(2)  From  a  specially  prepared  demonstration  slide  of  the  cerebellum 
(Golgi  technic)  make  a  diagram  (410)  showing  the  location  and  inter- 
relations of  the  constituent  cells  and  fibers:    In  the  molecular  layer,  the 
large  ('basket')  and  small  cortical  cells;  the  Purkinje  cells;  and  in  the 
nuclear  layer,  the  granule  cells,  eosin  bodies,  large  stelate  cells,  and  the 
solitary  cells.    In  the  medulla  note  the  axons  of  the  Purkinje  cells,  the 
mossy  fibers  and  the  climbing  fibers.     What  is  the  significance  of  the 
eosin  bodies?    Eelation  between  granule  cells  and  mossy  fibers?    How 
does  a  sagittal  section  differ  in  appearance  from  a  frontal  section,  with 
respect  to  the  Purkinje  cells  and  the  large  cortical  (basket)  cells?    Note 
also  the  types  and  disposition  of  the  neuroglia  cells. 

(C)'   THE  CEREBRAL  CORTEX  (Pallium). 

(1)  Study  l.p.  a  stained  (hematoxylin  and  eosin)  vertical  section  of 
the  human  cerebral  cortex  in  the  motor  area  (precentral  gyrus).     Note 
the  arrangement  of  the  cells  into  five  tangential  strata :  molecular  layer, 
outer  polymorphous  cell  layer,  small  pyramidal  cell  layer,  large, pyramidal 
cell  layer,  and  inner  polymorphous  cell  layer.    Sketch  (411).     Compare 
with  similar  sections  from  the  parietal  lobe  (a  sensory  area),  the  visual 
area  of  the  occipital  lobe,  the  auditory  area  of  the  temporal  lobe,  and 
the  olfactory  area  of  the  hippocampal  gyrus.     Note  also  the  cerebral 
meninges  (dura  mater,  arachnoidea,  and  pia  mater)   and  the  enclosed 
lymph  spaces.     Describe  the  granulationes  arachnoidales   (Pacchionian 
bodies;  arachnoidal  villi). 

(2)  From  a  Golgi  preparation  of  the  motor  cortex,  sketch  (412)  a 
segment  showing  the  character  and  arrangement  of  the  neurons  and  the 
neuroglia  elements.    Identify  a  cell  of  Betz;  a  cell  of  Martinotti.     Sig- 
nificance of  these  cells  ?    Distribution  of  the  'solitary  cells'  of  Meynert  ? 

(3)  From  a  Weigert-Pal  preparation  of  the  motor  cortex  sketch 
(413)  the  arrangement  of  the  nerve  fibers.     Note  the  bands  of  radial 


DIRECTIONS  FOR  LABORATORY  WORK  819 

fibers  alternating  with  the  interradial  feltwork;  the  supraradial  felt- 
work  ;  and  the  tangential  fiber  strata :  the  stratum  zonale,  the  stripe  of 
Bechterew,  and  the  outer  and  inner  stripes  of  Baillarger.  Relation  of 
the  tangential  stripes  to  the  cell  strata  ?  Compare  with  a  similar  prep- 
aration of  the  visual  cortex.  Define  the  stripe  of  Gennari. 


INDEX 


Abiogenesis,  17 

Absorption,  bone,  83 

Accessory  suprarenal,  556 

Accessory  thyroid,  562 

Acervulus,  584 

Aceto-carmin  stain  for  tissues,  744 

Acid  dyes,  740 

Acidophil  cells,  of  small  intestine,  371 

of  pituitary  body,  576 
Acoustic  meatus,  external,  683 
Acoustic  nerve,  712 

cochlear  branch  of,  712 
spiral  ganglion  of,  712 

vestibular  branch  of,  712 

vestibular  ganglion  (of  Scarpa),712 
Acromegaly,  573 
Adenoid  tissue,  84 
Adipose  tissue,  61 

Adrenal  (suprarenal)  gland,  blood  sup- 
ply of,  554-555 

cells  of  medulla,  553 

chromaffin  granules  in,  554 

lymphatics  and  nerves  of,  556 

zona  fasciculata  of,  552 

zona  glomerulosa  of,  552 

zona  reticularis  of,  553 
Adrenalin  (epinephrin),  549-554 
Adrenin,  549 
Agminate    nodules    of    small    intestine 

(Peyer's  patches),  366 
Alcohol  for  fixation  of  tissues,  724 
Alimentary  canal,   fibroserous  coat  of, 
345 

glands   of,    (crypts   of   Lieberkiihn), 
366 

ileocecal  valve  of,  379 

intestinal  villi  in,  366 

intestine,  large,  377 

appendices  epiploicee  of,  377 


Alimentary     canal,      intestine,      large, 

lymphoid   tissue   and   lymph   nodes 
of,  378 

mucous  membrane  of,  377 

plicae  semilunares  of,  377 

rectum  of,  379 

sacculations  or  haustra  of,  377 

tenise  (lineae)  coli,  377 

vascular  and  nerve  supply  of,  379 

vermiform  appendix  of,  378 
intestine,  small,  375 

absorption  from,  375 

agminate     nodules     of      (Peyer's 
patches),  366 

blood  supply  of,  373 

corium  of,  366 

duodenal     glands     of     (Brunner's 
glands),  365-372 

granules  of  Paneth  in,  370 

intestinal  glands  of,  370 

intestinal  villi  in,  368 

lacteals  of,  369-374 

lining  epithelium  of,  369 

lymphatics  of,  374 

mucous  membrane  of,  366 

nerve  supply  of,  374 

Peyer's  patches  in,  366 

solitary  nodules  of,  366 

structure  of,  363 

submucosa  of,  364 

valvulffl  conniventes  of,  364 
mucous  membrane  of,  347 
muscular  coat  of,  346 
submucous  coat  of,   346 
stomach,  blood  supply  of,  360 

cardiac  glands  of,  360 

fundus  glands  of,  354 

lenticular  glands  of,  360 

lymphatics  of,  362 


821 


822 


INDEX 


Alimentary     canal,     stomach,     mucous 

coat  of,  353 
muscular  coat  of,  353 
nerve  supply  of,  362 
oxyntic   or   delomorphous   cells   of, 

356 
peptic    or   auelomorphous   cells   of, 

355 

parietal  cells  of,  356 
pyloric  glands  of,  357 
secretion  of,  357 
serous  coat  of,  352 
submucous  coat  of,  353 
Alimentary  tract,  tabular  statement  of 

characteristics,  381 

Alum  carmin  for  staining  tissues,  744 
Alum   hematein    (Mayer)    for   staining 

tissues,  741 
Ameboid  mobility,  16 
Ameloblasts    (adamantoblasts),   333 
Amitosis,  19 
Anaphase,  25 
Anatomy,  microscopic,  1 
Angioblast,  215 

Annulus  tympanicus  of  ear,  685 
Anterior  chamber  of  eye,  636 
Appendix  epididymis,  502 
Appendix  testis,  502 
Appendix  vermiformis,  378 
Aqueductus    Fallopii,    relations    of,    to 

ear,  686 

Aqueous  humor  of  eye,  665 
Arachnoid  membrane,  620 
granulations,  621 
villi,  621 

Arciform  veins  of  kidney,  443 
Areas  of  Cohnheim  in  muscle,  112 
Areolar  connective  tissue,  56 
Arterial    wall,    general    characteristics 

of,  180 
Arteries,  176 

anterior  ciliary,  of  eye,  673 
anterior  spinal,  624 
arciform,   of   kidney,   440 
arteria  centralis  of  retina,  664,  670 
arterise  propriaj  renales,  440 
arterise  rectse  of  kidney,  441 


Arteries,  atypical,  structure  of,   182 

auditory,  714 

bronchial,  317 

central,  of  retina,  664,  670 

circle  of  Willis,  of  brain,  624 

circle  of  Zinn,  of  eye,  672 

cortical,  of  cerebrum,  625 

external  elastic  membrane  of,  179 

fissural,  of  brain,  625 

helicine,  of  corpus  cavernosum  penis. 
504 

hyaloid,  of  eye,  672 

interlobular,  of  kidney,  441 
of  liver,  415 

internal  elastic  membrane  of,  178 

large,  structure  of,  181 

large  and  small  compared,  184 

long  ciliary,  of  eye,  672 

medium-sized,  coats  of,  177 

medullary,  of  cerebrum,  625 

middle  cerebral,  625 

pulmonary,  314 
structure  of,  183 

precapillary,  structure  of,  182 

short-ciliary,  of  eye,  672 

small,  structure  of,  181 

tunica  adventitia  of,  177-178 

tunica  intima  of,  177 

tunica  media  of,  177-178 

umbilical,  structure  of,  182 

vasa  vasorum  of,  180 
Arterioles,  structure  of,  181 
Atrioventricular  bundle  of  His,  102 
Auerbach's  fuchsin  methyl  green  stain, 

756 
Auditory   area   of   cerebral   cortex,   cell 

layers  of,  618 
Auditory  canal,  683 
Auditory  ossicles,  689 
Auditory  tube  of  ear,  691 
Auerbach's  stain  for  chromatin,  756 
Auricle  or  pinna  of  external  ear,  682 
Axis  cylinder,  the,  132 
Axon,  the,  128 

Balsam     (Canada)     for    mounting    sec- 
tions, 760 


INDEX 


823 


Bartholin's  glands  of  the  vulva,  541 
Basic  dyes,  740 
Basket  cells  of  cerebellum,  608 
Basophilic  cells  of  pituitary  body,  576 
Bellini's  ducts  of  kidney,  438 
Benda's     technic      for      demonstrating 

mitochondria,  757 
Berlin  blue  gelatin   mass  for  injection 

of  tissues  and  organs,  732 
Betz  cells  of  cerebral  cortex,  613 
Bibliography  of  histologic  technics,  761 
Bioplasm,  1 
Bladder,  urinary,  448 
Blastomeres,  27 
Blood,  203 

angioblast,  215 

coagulation  of,  214 

development  of,  24 

fibrin  of,  203 

hematin  of,  212 

hematoidin,  214 

hemin,.212 

hemoglobin  of,  203-211 

hemokonia  of,  206 

hemolysis  of,  206 

hemosiderin,  213 

hypertonic  solution  for,  206 

hypotonic  solution  for,  206 

isotonic  solution  for,  206 

leukoblasts  in,  218 

mononuclear  leukocytes  in,  218 

oxyhemoglobin,  211 

prothrombin,  203 

Teichmann's  crystals  in,  212 

thrombin,  203 
Blood  cells,  basophils,  210 

crenation  of,  206 

dyes  for,  210 

eosinopliils,   210 

erythroblasts,  217 

erythrocytes,  203-217 

erythroplastids,  203-217 

giant,  209-218 

granuloeytes,  209 

hyaloplasm  of,  206 

ichthyoid  stage,  217 

leukocytes,  203 


Blood  cells,   lymphocytes,  207 

megaloblasts,  217 

megalocytes,  209 

neutrophils,  209 

non-granular  leukocytes,  208 

normoblasts,  217 

plastids,  203 

plates  (plaques),  209 

polykaryocytes,  209 

primitive,  derivatives  from,  219 

red,  203 

rouleaus,  206 

sauroid  stage,  217 

spindle  cells,  209 

spongioplasm  of,  206 

thrombocytes,  209 

transitional  leukocytes,  208 

white,  207 
Blood  clot,  203 
Blood  corpuscles,  203 

crenated  corpuscles,  206 
Blood  crystals,  212 
Blood  plasma,  203 
Blood  platelets,  203-209 
Blood  serum,  203 
Blood  shadows,  206 

Blood     stain,     eosinate     of     methylene 
blue,  Hastings'  method,  754 
Blood  vascular  system,  176 
Blood   vessels,   circulus   major   of   iris, 
672 

circulus  minor  of  iris,  673 

development  of,  192 

essential  structure  of,  194 

fetal,  538 

of   brain   and    spinal   cord,    619-624 
625 

of  bronchi,  317 

of  eye,  636-643-664-670-673 

of  eyelids,  678 

of  heart,  201 

of  internal  ear,  714 

of  kidney,  440-444 

of  large  intestine,  379 

of   liver,   415-417 

of  lungs,  314 

of  lymph  nodes,  242 


824 


INDEX 


Blood  vessels,  of  mammary  gland,  547 

of  middle  ear,  693 

of  olfactory  mucosa,  298 

of  ovary,  522 

of  oviduct,  527 

of  pancreas,  403 

of  parathyroid  glands,  565 

of  penis,  503-504 

of  prostate  gland,  500 

of  renal  pelvis  and  ureter,  448 

of  salivary  glands,  392 

of  skin,  290 

of  small  intestine,  373 

of  spleen,  246 

of  stomach,  360 

of  suprarenal  gland,  554 

of  thymus  gland,  568 

of  thyroid  gland,  560 

of  tongue,  343 

of  urinary  bladder,  452 

of  uterus,  532 

Bohmer's  hematoxylin  for  staining  tis- 
sues, 741 
Bone,  72 

absorption  of,  83 

cancellous,  85 

canaliculi  of,  75 

circumferential   lamellae   of,   76 

compact,  74 

development  of,  79 

diploe  of,  88 

endochondrial  ossification,  85 

epiphyseal  line,  85 

epiphyseal  ossification,  85 

external   circumferential    lamellae   of, 
84 

general  considerations  of,  72 

Haversian  canals  of,  85 

Haversian  lamellae  of,  75 

Haversian  spaces  of,  84 

Haversian  systems  of,  75-84 

internal    circumferential    lamellae    of, 
85 

interstitial  lamellae  of,  76-85 

intramembranous  ossification,  86 

lacunae  of,  75 

lacunee  of  Howship,  of,  84 


Bone,  lymphatics  of,  78 

nerves  of,  78 

osteoblasts  of,  83 

osteoclasts  of,  77 

periosteum  of,  74 

primary,  83 

red  marrow  of,  77 

tables  of, -88 

Volkmann's  canals  of,  76 
Bone  marrow,  77-220 
Bone    marrow    cells,    basophil    granulo- 
cytes,  223 

eosinophil   granulocytes,    222 

erythrocytes,  224 

giant  cells,  223 

hemoblasts,  221 

large  mononuclear  leukocytes,  222 

lymphocytes,  221-222 

mast  cells,  223 

mesameboid  cells,  221 

myeloblasts,  221 

myelocytes,  220 

myeloplaxes,  223 

polymorphonuclear    neutrophil    gran- 
ulocytes, 222 

premyelocytes,  221 

primitive  blood  cells,  221 
Bony  labyrinth  of  the  internal  ear,  694 
Borax  carmin  stain  for  tissue,  743 
Bouin's    fluid    for    fixation  of    tissues, 

729 
Bowman's  elastic  membrane  of  cornea, 

631 

Box  for  embedding  in  paraffin,  737 
Brain  sand    (acervulus),  584 
Bronchi,  304 

structures  of,  304 
Bronchial  arteries,  317 
Bronchioles,  307 
Brownian  movement,  17 
Bursae,  117-233 

Cajal's      method      for      demonstrating 

neurofibrils,  750 
Calcified  cartilage,  80 
Canal  of  Stilling   (canalis  hyaloideus), 

672 


INDEX 


825 


Capillary  plexuses,  187 
Capillary  wall,  stigmata  of,  186 
Capillaries,  structure  of,  184 
Cardiac  glands  of  the  stomach,  36S 
Cardiac  muscle,  94,  99 
Cardiac    muscle,    intercalated    discs   of, 
Zimmerman 's      method      of 
staining,  758 

Cardiac  Purkinje  fibers,  102 
Cardiac  plexus,  origin  of,  591 
Carmin   gelatin   mass   for   injection   of 

tissues  and  organs,  732 
Carmin  stain  for  tissues,  743 
Carnoy's   fluid   No.    1   for   fixation   of 

lung  tissue,   729-730 
Carotid  gland,  the,  569 
Cartilage,  67 

blastema  of,  69 

calcified,  80 

cells,  enlargement  of,  80 

elastic,  71 

fibro-,  71 

hyaline,  68 

matrix  of,  69 

origin  of,  70 

primordial  marrow  cavities  in,  82 
Cell,  definition  of,  1 
Cell  layers  of  motor   area  of  cerebral 

cortex,  615,  616 
Cell  plate  (midbody),  25 
Celloidin,  adhesive  for  sections,  739 

embedding  of  tissues  in,  734 
Cells,  acidophil,  of  parathyroid,  564 

acidophilic,       of       pituitary       body, 
576 

acidophil,  of  small  intestine,  371 

amitosis  of,  19 

anaphase  of,  division  of,  25 

archoplasm  of,  7 

astral  rays  of,  7 

astral  system  of,  7 

basophilic,  of  pituitary  body,  576 

basket,  of  salivary  glands,  385 

basophil  granules  of,  52 

Betz,  of  cerebral  cortex,  613 

cartilage,  enlargement  of,  80 

cementum,  of  teeth,  337 


Cells,  of  cerebral  cortex,  Golgi's,  types 

1  and  2,  613 

centro-acinal,  of  Langerhans,  396 
centriole  of,  7 
centrosome  of,  7 
centroplasm  of,  7 
centrosphere  of,  7 
chondrioconts  of,  8 
chondriomites  of,  8 
chromaffm  of  small  intestine,  371 
chromafEn,  of  suprarenal  gland,  548 
chromidia  of,  8 

chromophobe,  of  pituitary  body,  576 
chromosomes  of,  24 
cilia  of,  16 
close  spireme,  24 
connective  tissue,  51 
cytology  of,  1 
cytoplasm  of,  7 

decidual,  of  gravid  uterus,  535 
deutoplasm  of,  8 
diplosome  of,  7-24 
division  of,  18 
eosinophil  granulocytes,  52 
ependyma,  of  nervous  system,  589 
general  statements  in  regard  to,  5 
hepatic,  412 

pigment  in,  414 
goblet,  of  small  intestine,  370 
granular,  of  cerebellum,  609 
granule  of  Paneth  in  small  intestine, 

370 

kinoplasm  of,  7 
lamellar,  52 
of    Langhans,    of    choriomc    villi    of 

gravid  uterus,  537 
large  stellate,  of  cerebellum,  609 
loose  spireme  of,  24 
lutein,  of  ovary,  519 
of  Martinotti  of  cerebral  cortex,  617 
mastoid,  of  ear,  686 
metaphase,  of  division,  25 
metaplasm  of,  8 
microsome  of,  8 
mitochondria  of,  8 
mitosis  of,  22 
nucleus  of,  6 


826 


INDEX 


Cells,    neuroglia,    of    nervous    system, 
589 

osteoblasts,  77 

osteoclasts,  78 

parietal    (oxyntic   or   delomorphous) , 
of  stomach,  356 

peptic    or    adelomorphous,    of    stom- 
ach, 355 

pheochrome,     of     suprarenal     gland, 
548 

pigment,  52 

plasma  of,  51 

plastosomes  of,  8 

prickle,  44 

pseudochromosomes  of,  8 

Purkinje,  of  cerebellum,  607 

pyramidal,  of  cerebral  cortex,  613 

reproduction  of,  17 

resting  nucleus  of,  24 

segmented  spireme  of,  24 

Sertoli,  of  seminiferous  tubules,  481 

small  cortical,  of  cerebellum,  608 

solitary,  of  Meynert  of  cerebral  cor- 
tex, 613-618 

spindle,  51 

telophase  of,  division  of,  25 

tendon,  117 

interstitial,  of  Leydig  of  testis,  487 

trophospongium  of,  8 

varieties  of,  32 

vital  properties  of,  14 
Cement  substance,  intercellular,  30 

nitrate  of  silver  stain  for,  752 

terminal  bars  of,  34 
Cementoblasts,  337 
Cementum,  development  of,  336 
Centers  of  ossification,  79 
Central  artery  of  retina,  664 
Central   nervous    system,    blood    supply 
of,  624 

veins  of,  625 
Central  spindle,  25 
Cerebellum,  603 

basket  cells  of,  608 

climbing  fibers  of  medulla  of,  609 

cortex  of,  606 

granule  cells  of,  609 


Cerebellum,  large  stellate  cells  of,  609 

medulla  of,  609 

Purkinje  cells  of,  607 

resume  of  structures  of,  611 

small  cortical  cells  of,  608 
Cerebral  cortex,  611 

auditory  area,  cell  layers  of,  618 

cell  layers  of  motor  area,  615,  616 

cells    (solitary)    of  Meynert,  613-618 

fiber  tracts  of,  618 

Golgi's  types  of  cells  of,  613 

motor  area  of,  615 

motor  area,  cells  of  Martinotti  of,  617 

nerve  cells  of,  612 

olfactory  area,  cell  layers  of,  618 

stripes  of  Baillarger,  619 

stripe  of  Bechterew,  619 

visual  area,  cell  layers  of,  617 
Cerebrum,  cortical  arteries  of,  625 

lobes  of,  611 

medullary  arteries  of,  625 

meninges  and   blood  supply  of,   619- 
620-621 

middle  cerebral  artery  of,   625 
Cervical  glands  of  uterus,  532 
Ceruminous  glands  of  ear,  684 
Chondrioconts,  50 
Chondroclasts,  82 
Chordae  tendinea3  of  heart,  197 
Chorionic  villi,  537 
Choroid  coat  of  eye,  636 

lamina  basalis  of,  637 

lamina  capillaris  of,  636 

membrane  of  Bruch,  637 

suprachoroid  layer  of,  636 

tapetum  cellulosum  of,  638 

tapetum  fibrosum  of,  637 

tunica  Ruyschiana  of,  637 

vascular  layer  of,  636 
Choroidal  fissure  of  the  eye,  645 
Chromaffin  cells  of  small  intestine,  371 

of  suprarenal  gland,  548 
Chromaffin    granules,   technic   for   dem- 
onstrating, 759 
Chromaffin  system,  571 
Chromatin,  Auerbach's  fuchsin  methyl- 
green  stain  for,  756 


INDEX 


827 


Chromidia,  in  spermatogenesis,  474 
Chromo-acetic     formalin     mixture     for 

fixation  of  tissues,  727 
Chromophobe    cells   of    pituitary    body, 

576 
Chromosomes,  24-476 

sex,  in  spermatogenesis,  475 

in  spermatogenesis,  464 
Chyle,  226 

in  small  intestine,  374 
Cilia,  16 
Ciliary  body  of  eye,  638 

fibrous  layer  of,  640 
Ciliary  epithelium  of  eye,  640 
Ciliary  glands  of  eye,  640 
Ciliary  motility,  16 
Ciliary  processes  of  eye,  638 
Oiliary  muscle  of  eye,  638 
Circle  of  Willis,  604 
Circle  of  Zinn,  672 
Circulus  venosus  of  Haller,  547 
Ciliated  epithelium,  40 
Clarification  of   sections,  759 
Classification  of  dyes,  740 
Clitoris,  541 

Coagulation  of  blood,  214 
Coccygeal  gland,  570 
Cochlea  of  internal  ear,   accessory  tec- 
torial  membrane  of,  706 

basilar  membrane  of,  706 

cochlear  artery  of,  714 

function  of,  716 

hamulus  of,  701 

Hensen's    stripe    of    tectorial    mem- 
brane in,  706 

limbus  spiralis  of,  705 

membrana     tectoria     (membrane     of 
Corti),  705 

membranous   wall   of    scala   tympani 
and  scala  vestibuli,  704 

organ  of   Corti,  708 

varieties  of  cells  of,  70&-709 

prominentia  spiralis  of,  705 

spiral  ligament  of,  704 
stria  vascularis  of,  705 

structure  of,  701 

sulcus  spiralis  externus  of,  705 


Cochlea  of  internal  ear,  sulcus  spiralis 
internus  of,  706 

vestibular  membrane  of  Keissner,  704 
Collagen,  57 

Colloid  in  thyroid  gland,  557 
Coloboma,  eye,  646 
Colostrum,  546 
Columnar  earnae,  198 
Comparison  of  artery  with  vein  of  cor- 
responding size,   79 
Concentric     corpuscles      (Hassall)      of 

thymus,  567 

Congo  red  for  tissue  stain,  746 
Conjunctiva,  ocular,  674 

palpebral,  674 

Conarium   (pineal  body),  579 
Connective  tissue,   Mallory's  stain  for, 

753 

Conus  medullaris,  600 
Corium  of  skin,  268 
Cornea  of  eye,  630 

anterior   homogeneous   membrane   in, 
631 

Bowman's  elastic  membrane  of,  631 

endothelium  of,  633 

epithelium  of,  631-633-674 

layers  of,  631 

membrane  of  Descemet,  632 

posterior  epithelial  layer  of,  633 

posterior  homogeneous  membrane  of; 
632 

vascular  and  nerve  supply  of,  633 
Corneal  corpuscles,  631 
Corneal  epithelium,  631-674 
Corneal  substance,  631 
Corpora  albicantia,  of  ovary,  510 
Corpora  lutea  spuria,  521 
Corpora     lutea     vera     of     pregnancy, 

521 
Corpus  cavernosum  penis,  503 

helicine  arteries  of,  504 

pectiniform  septum  of,  504 

tunica  albuginea  of,  504 
Corpus  hemorrhagicum  of  ovary,  519 
Corpus   Highmori   testis,   480 
Corpus  luteum  of  ovary,  519 
Corpus  spongiosum  penis,  503-506 


828 


INDEX 


Corpuscles,  Pacinian,  174 
Cover  glass,  how  to  apply,  722 
Cowper's  glands  of  urethra,  501 
Cretinism,  561 
Crusta  petrosa  of  teeth,  329 
Crystalline  lens  of  eye,  666 

capsule  of,  666 

lenticular  epithelium  of,  666 

nuclear  zone  of,  667 

nucleus  of,  667 

substantia  lentis,  666 

suspensory  ligament  of,  669 
Cutaneous  appendages,  271 
Cutis  vera,  268 
Cytogenesis,  1 

Cytologic  stain,  Ehrlich  triacid,  755 
Cytology,  1 
Cytolymph,  8 
Cytomorphosis,  29 
Cytoplasm,  7 
Cytoplasmic  dyes,  745 
Cytoplasmic  granules,  eosin  and  methyl 
blue  mixture    (Mann),  stain 
for,  755 
Cytoreticulum,  8 

Dartos  of  scrotum,  481 
Decalcification   of  tissues,   731 
Decidua  reflexa  of   the   gravid  uterus, 

537 

Decidua  vera  of  the  gravid  uterus,  537 
Delafield's     hematoxylin     for     staining 

tissues,  742 

Dendrons  (dendrites),  128 
Dental  cement,  329 
Dental  cuticular  membrane, 
Dental  enamel,  layers  of,  335 
Dental  groove,  330 
Dental  lamina,  330 
Dental  papilla,  330-336 
Dental  pulp,  323 

odontoblasts  in,  324 
Dentin,  325 

contour  lines  of  Owen  in,  327 

globules  in,  326 

granular  layer  of  Tomes  in,  327 

incremental  lines  of  Schreger  in,  327 


Dentin,  interglobular  spaces   of,  326 
sheaths  of  Neumann  in,  327 
tubules  in,  326 
Derma,  268 

Descemet's  membrane  of  cornea,  632 
Determiners,  chromosomal  in  sex  hered- 
ity, 477 
Digestive  system,  320 

alimentary   canal,   character   of    wall 

in,  344 

fibroserous  coat  of,  345 
mucous  membrane  of,  347 
muscular  coat  of,  346 
submucous  coat  of,  346 
esophagus,  coats  of,  348 
glands  of,  351 
mucous  coat  of,  350 
muscular  coat  of,  350 
ileocecal    (colic)   valve,  379 
intestinal   glands    (crypts  of  Lieber- 

kiihn),  366 
intestine,  large,  377 

appendices  epiploicae  of,  377 
lymphoid   tissue   and  lymph   nodes 

of,  378 

mucous  membrane  of,  377 
plicas  semilunares  of,  377 
rectum,  379  ^  • 

sacculations  or  haustra  of,  377 
tenise   (lines)   coli,  377 
vascular     and     nerve     supply     of, 

379 

vermiform  appendix,  lymphoid  tis- 
sues in,  378 
intestine,     small,     absorption     from, 

375 
agminate     nodules     of      (Peyer's 

patches),  366 
blood  supply  of,  373 
corium  of,  366 
duodenal  glands   (Brunner's),  365- 

372 
granule   cells   of   Paneth    in,    370- 

371 

intestinal  glands  of,  370 
intestinal  villi  in,  368 
lacteals  of,  369-374 


INDEX 


829 


Digestive   system,   intestine,   small,  lin- 
ing epithelium  of,  369 

lymphatics  of,  374 

mucous  membrane  of,  366 

nerve  supply  of,  374 

Peyer's  patches,  366 

solitary  nodules  of,  366 

structure  of,  363 

submucosa  of,  364 

valvute  conniventes  of,  364 
liver,  bile  capillaries  of,  411 

blood  supply  of,  417 

capsule  of  Glisson  of,  408 

cells  of,  412 

course  of  blood  through,  419 

gall-bladder,  420 

hepatic  connective  tissue  in,  408 

hepatic  lobule,  409 

interlobular  arteries  and  veins  of, 
415 

interlobular  bile  ducts,  415 

lymphatics  of,  419 

nerves  of,  420 

pigment  cells  in,  414 

portal  canals,  408-415 

structure  of,  405 
mouth,  320 

lymphoid   tissues   in   mucous  mem- 
brane of,  321 

mucous  membrane  of,  320 

secreting   glands    in   mucous   mem- 
brane of,  321 
pancreas,  394 

acini  of,  396 

blood  supply  of,  403 

nerve  supply  of,  404 

resume,  404 
pharynx,  347 
portal  vein,  417 
salivary  glands,  382 

blood  supply  of,  392 

general  considerations  of,  382 

mucous  acini  of,  386 

nerve  supply  of,  393 

parotid  gland,  390 

serous  acini,  385 

sublingual  gland,  392 


Digestive  system,  salivary  glands,  sub- 
maxillary  gland,  391 
stomach,   360 

blood  supply  of,  360 

cardiac  glands  of,  360 

fundus  glands  of,  354 

lenticular  glands  of,  360 

lymphatics  of,  362 

mucous  coat  of,  353 

muscular  coat  of,  353 

nerve  supply  of,  362 

peptic   or  adelomorphous   cells  of, 
355 

parietal  cells  (oxyntic  or  delomor- 
phous  cells)   of,  356 

pyloric  glands  of,  357 

serous  coat  of,  352 

secretion  of,  357 

submucous  coat  of,  353 
teeth,  337 

ameloblasts    (adamantoblasts)    of, 
333 

cementoblasts  of,  337 

cementum,  329 

development  of,  336 

deciduous,  331 

papilla  of,  336 

pulp  of,  323 

dentin  of,  325 

development  of,  330 

enamel  of,  328 

enamel  germ  of,  330-331 

enamel  layers  of,  335 

enamel  organ  of,  330 
layers  of,  331 
Tome's  processes  in,  333 

odontoblasts,  324 

odontoclasts,  337 

permanent,  331 

structure  of,  323 
tongue,  337 

blood  vessels  of,  343 

foramen  cecum  of,  343 

lymphatics  of,  344 

mucous  membrane  of,  337 

muscle  fibers  of,  337 

nerve  supply  of,  344 


830 


INDEX 


Digestive    system,    tongue,    papillae    of, 

339,  340,  341 
taste  buds  of,  341 
tonsil  of,  343 
Diploe,  of  bone,  88 
Diploid  number  of  chromosomes,  363 
Diplosome,  24 

Double  staining  of  tissues,  746 
Ductless  glands,  260-548 

hormones  of,  586 

Ductuli   aberrentes,   mesonephric,   502 
Duodenal     glands      (Brunner's),     365- 

372 

Dura  mater,  620 
Dyes,  740 

acid,  740 

basic,  740 

classification  of,  740 

cytoplasmic,  745 

mordants  for,  741 

neutral,  740 

specific,  740 
Dyspituitarism,  573 

Ear,  717 

development  of,  717-719 
external,  682 

acoustic  meatus  of,  683 
auricle  of,  682 

ceruminous  glands  of  auditory  ca- 
nal, 684 
pinna  of,  682 
internal,  712 

acoustic  nerve,  712 

cochlear  branch  of,  712 
vestibular    ganglion    of    Scarpa, 

712 

aqueductus  vestibuli  of,  694 
auditory  artery,  714 
blood  supply  of,  714 
bony  labyrinth  of,  694 
canalis    communis    of    semicircular 

canals,  699 
cochlea,   706 

accessory  tectorial  membrane  of, 

706 
basilar  membrane  of,  706 


Ear,   internal,   cochlea,   ceeum   vestibu- 

lare  of  scala  media,  703 
cochlear  artery,   714 
cochlear    nerve,    spiral    ganglion 

of,  712 

cupola  of,  701 
development  of,   719 
foramina  nervosa  of,  702 
function  of,  716 
hamulus  of,  701 
helicotrema  of,  703 
Hensen  's  stripe  of  tectorial  mem- 
brane in,  706 
lagena    or    cecum    cupulare    of 

scala  media  in,  703 
limbus  spiralis  of,  705 
membrana  tectoria,  membrane  of 

Corti,  703-705 
membranous  wall  of  scala  tym- 

pani  and  scala  vestibuli,  704 
organ  of  Corti,  708,  709-710 
organ  of  Corti,  cells  of,  708-709 
prominencia  spiralis  of,  705 
scala    media,    or    cochlear    duct, 

703 

scala  tympani,  701 
secondary     tympanic     membrane 

of,  703 

scala  vestibuli  of,  701 
spiral  ligament  of,  704 
spiral   ligament,   stria  vascularis 

of,  705 

spiral  organ  of  Corti,  702 
structure  of,  701 
sulcus  spiralis  externus,  705 
sulcus   spiralis  internus,   703-706 
vestibular  membrane  of  Eeissner, 

703-704 

vestibular  artery,  714 
cupola    of    semicircular    canals   in 

700 

ductus  endolymphaticus,  694 
endolymph  of,  695 
cndolymphatic  sac,  694 
fenestra  vestibuli,  693 
general  considerations  of,  693 
internal  auditory  vein,  716 


INDEX 


831- 


Ear,    internal,    cochlea,    lymphatics    of, 

716 

macula  acustica  sacculi,  697 
macula  acustica  utriculi,  698 
membranous  labyrinth,  694 
neuro-epithelium  of  saccule,   695 
neuro-epithelium,  varieties  of,  697 
organ  of  equilibration,  700 
otoliths  in,  697 
otocyst,  699 
perilymph  of,  695 
saccule  of,  694 
sacculus  of  vestibule  in,  694 
semicircular  canals  of,  699 

ampullae  of,  699 
utricle  of,  698 
utriculosaccular  canal  of  vestibule, 

694 

utriculus  of  vestibule,  694 
veins  of,  715-716 
vestibule,  of,  693 
middle,  686 

aqueductus    Fallopii,    relations   of, 

686 

annulus  tympanicus,  685-687 
auditory  canal,  683 
auditory  ossicles  of,  689 
auditory  tube    (Eustachian  tube), 

691 

blood  vessels  of,  693 
epitympanic  cavity  of,  685 
Eustachian  tube,  691 
fenestra  ovalis  of  tympanum,  686 
fenestra  rotunda  of  tympanum,  685 
general  considerations  of,  685 
incus,  689 

orbicular  process  of,  689 
lymphatics  of,  693 
malleus,  689 

ligaments  of,  691 
mastoid  cells,  686 
membrana  flaccida  of,  689 
Prussak's  space,  691 
Shrapnell's  membrane,  689 
stapedius  muscles  of,  690 
stapes,  689 
tensor  tympani  muscle,  690 


Ear,      middle,      tympanic      membrane, 

687 

tympanic  mueosa,  686 
tympanum,  685 

pelvis  ovalis  of,  686 
processus  cochleariformis  of,  690 
promontory  of,  685 
tubal  tonsil  of,  692 
umbo    of    tympanic    membrane    in, 

687 

Ectoderm,  28 

Ehrlich's  triacid  stain,  755 
Ejaculatory  ducts,  497 
Elastic  fibers,  57 

Elastic  tissue,  Weigert's  stain  for,  753 
Elastin,  58 
Eleidin,  45 

Embedding,  in  paraffin,  box  for,  737 
of  tissues,   734 
in  celloidin,  734 
in  paraffin,  735 

Embryonic  connective  tissue,  50-53 
Enamel,  328 

contour  lines  of  Eetzius  in,  329 

prism,  328 

radial     lines     or     prism     stripe     of 

Schreger  in,  329 
Enchylema,  8 
Endocardium,  195-196 
Endocrin  glands,  260-548 

hermones  of,  586 
Endomysium,   195 
Endothelium,  37 

Enlargement  of  cartilage  cells,  80 
Entodorm,  28 
Eosin,  as  a  tissue  stain,  745 

and    methyl    blue    mixture    (Mann), 
stain   for   cytoplasmic   gran- 
«  ules,  755 

Eosinate  of  methylene  blue  stain 
(Basting's  method)  for 
blood,  754 

Ependyma  cells,  141-589 
Epicardum,  195 
Epicritic  sensibility,  164 
Epidermis,  262 
Epididymis,  492 


832 


INDEX 


Epidural  space,  620-623 
Fpinephrin   (adrenin),  549 
Epiphysis  cerebri,  579 

blood  supply  of,  584 

development  of,  580 

function  of,  &81 

habenular  commissure  of,  581 

histologie  structure  of,  582 

nerves  of,  584 

posterior  commissure  of,  581 
Epithelia,  classification  of,  34 
Epithelial  tissues,  30-33 
Epithelium,  40 

ciliated,  40 

endothelial,  37 

glandular,  40 

goblet  cell,  41 

mesothelial,  37 

modified  columnar,  40 

neuro-,  42 

non-stratified,  37 

pavement,  37 

plain,  39 

pseudo-stratified  columnar,  46 

simple  columnar,  39 

simple  squamous,  37 

stratified,  43 

stratified  squamous,  43 

transitional,  47 

varieties  of,  33 

Epitympanic  cavity  of  ear,  685 
Epoophoron    (parovarium),    of    female 

genitalia,  539 
Equatorial  plate,  25 
Eruptive  tissue,  of  developing  bone,  82 
Esophagus,  348 

coats  of,  348 

glands  of,  351 

mucous  coat  of,  350 

muscular  coat  of,  348 

submucous  coat  of,  348 
Euparal,  for  mounting  sections,  74 
Eustachian  tube,  691 
Exophthalmic  goitre,  561 
External  ear,  682 
External  genitals,  female,  540 

clitoris,  541 


External     genitals,     female,     glandulae 
vestibulares       m  a  j  ores 
(Glands   of   Bartholin),   541 
glandulse  vestibulares  minores,  541 
hymen,  541 
labia  majora,  540 
labia  minora,  540 
vestibule,  540 

External  genitals,  male,  503 
penis,  503 

corpora  cavernosa  of,  503-504 

corpus  spongiosum  urethras  of,  506 

helicine  arteries  of,  504 

lymphatics  of,  506 

nerves  of,  506 

nervi  erigentes  of,  506 

pectiniform  septum  of,  504 

preputial  glands  of,  506 

tunica  albuginea  of  corpus  caverno- 
sum,  504 

Tyson's  glands  of,  506 
Eye,  anterior  chamber  of,  636-643 
appendages  of,  674 
aqueous  humor  of,  665 
blood    supply   of    sclerocorneal    junc- 
tion, 636 

blood  vessels  of,  670 
canalis  hyaloideus,   or  canal  of  Stil- 
ling, 672 
canal    of    Schlemm     (sinus    venosus 

sclerze),  635 
capsule  of  Tenon,  627 
choroid  coat  of,  636 

lamina  basalis  of,  637 

lamina  capillaris  of,  636 

membrane  of  Bruch,  637 

tapetum  cellulosum  of,  638 

tapetum  fibrosum  of,  637 

tunica  Euyschiana  of,  637 

vascular  layer  of,  636 
ciliary   arteries,    anterior,   673 

long,  672 

short,  672 
ciliary  body  of,  638 

fibrous  layer  of,  640 
ciliary  epithelium,  640 
ciliary  glands,  640 


INDEX 


833 


Eye,   ciliary  muscle,  638 
ciliary  processes,  640 
circle  of  Zinn,  672 
coats  of,  628 
conjunctiva,  674 
ocular,   674 
palpebral,  674 
contents  of,  665 
cornea,  630 

anterior  epithelium  of,  674 
anterior     homogeneous     membrane 

of,  631 

Bowman's  elastic  membrane  of,  631 
corpuscles  of,  631 
endothelium  of,   633 
epithelium  of,  631 
layers  of,  631 

membrane  of  Descemet,  632 
posterior  epithelial  layer  of,  633 
posterior    homogeneous    membrane 

of,  632 
substance  of   (substantia  propria), 

631 

vascular  and  nerve  supply  of,  633 
crystalline  lens  of,  666 
capsule  of,  666 
lenticular   epithelium   of,   666 
nuclear  zone  of,  667 
nucleus  of,  667 
substantia  lentis,  666 
suspensory  ligament  of,  669 
development  of,  645 
choroidal  fissure,  645 
optic  cup,  645 
optic  stalk,  645 
optic  vesicle,  645 
external  or  fibrous  tunic  of,  629 
general  considerations  of,  626 
gland  of  Harder,  681 
glaucoma,  635 
hyaloid  artery  of,  672 
hyaloid  membrane  of,  669 
iridocorneal  angle,  643 
iris,  641 

circulus  major  of,  672 
circulus  minor  of,  673 
coloboma  of,  646 


Eye,  iris,  color  of,  642 
dilator  muscle  of,  642 
endothelium  of,  641 
fibrous  stroma  of,  642 
internal  epithelium  of,  643 
layers  of,  641 
sphincter  muscle  of,  642 
lacrimal  gland,  679 
lacrimal  lake,  679 
ligamentum  pectinatum  of,  635-643 
lymphatic  systems  of,  673 
middle  coat  of,  vascular  tunic,  636 
muscas  volitantes,  669 
nerves  of,  674 
optic  nerve,  664 
optical  or  visual  axis,  628 
ora  serrata,  665 
pineal,  580 

posterior  chamber  of,  636-643 
retina  of,  644 

cell  types  of  inner  nuclear  layer  of, 
654-655-656 

central  artery  of,  664-670 

cones  of,  651-652-653 

external  limiting  membrane  of,  653 

fibers  of  Miiller  of,  658 

fiber  layer  of  Henle,  654 

fovea  centralis  of,  660 

ganglion  cell  layer  of,  657 

general  considerations  of,  644 

inner  nuclear  layer  of,  654 

inner  reticular  layer  of,  656 

inversion  of,  663 

layers  of,  646 

macula  lutea  of,  659 

nerve  fiber  layer  of,  657 

optic  papilla  of,  665 

optic  disk  of,  665 

outer  nuclear  layer  of,  654 

outer  reticular  layer  of,  654 

pigment  epithelium  of,  646 

porus  opticus  of,  665 

rods  of,  648-649-650 

rods    and    cones,    development   of, 
661-663 

layer  of,  647 

supporting  tissues  of,  658 


834 


INDEX 


Eye,  retina  of,  visual  purple  of,   647- 
649 

yellow  spot  of,  659 
sclerocorneal  junction  of,  635 
sclerotic  coat  of,  634 

corpuscles  of,  634 

lamina  fusca  of,  634 

lamina  cribrosa  of,  634 

pinguecula  of,   634 

substantia  propria  of,  634 
spaces  of  Fontana  of,  635-643 
.spatia    zonularis    of    (canals    of    Pe- 
tit), 670 

suprachoroid  layer  of,  636 
uvea  of,  636 
uveal  tract  of,  636 
vascular  tunic  of,  636 
vense  vorticosse  of,  672 
vitreous  humor  of,  669 
zonula  ciliaris  of  Zinn,  of,  670 
Eyelid,  674 

accessory  lacrimal  glands  of  Krause 

of,  677 

blood  supply  of,  678 
cutaneous  portion  of,  674 
conjunctival  portion  of,  676 
glands  of  Moll  of,  676 
glands  of  Zeiss  of,  676 
lymphatic  and  nerve  supply  of,  678 
palpebral  muscle  of  Miiller,  677 
posterior  tarsal  glands  of  Waldeyer, 

677 

tarsal  (Meibomian)  glands,  676 
tarsus  of,  676 

Fallopian  tube,  525 

blood  supply  of,  527 

mucosa  of,  526 

lymphatics  and  nerves  of,  528 

muscular  wall  of,  526 

serous  coat  of,  526 

structure  of,  525 
Female  reproductive  organs,  507.     See 

also  Reproductive  system. 
Fat,  osmic  acid  test  for,  758 

stains  for,  62,  759 
Fat  tissue,  61 


Fibers,  collagenous,  49 
elastic,  49-57 
white,  49 

Fiber    tracts    of    cerebral    cortex,    618. 
See  also  Nervous  system. 

Fibrocartillage,  71 

Filar  mass,  8 

Filum   terminale    of   spinal   cord,    600. 
See  Nervous  system. 

Flagellate  motion,  16 

Flagellum,   16 

Flemming's    fluid    for    fixation    of   tis- 
sues, 728 

Fontana,  spaces  of,  635.     See  also  Eye. 

Formalin,  for  fixation  of  tissues,  72."> 

Fovea  centralis  of  retina,  660.    See  also 
Eye. 

Fresh  tissues,  examination  of,  720 

Fuchsin  for  tissue  stain,  746 

Gage's      method      for      demonstrating 

glycogen,  750 
Gall-bladder,   420.      See    also   Digestive 

system. 
Gametogenesis,    460.     See   also   Eepro- 

ductive  system.- 

Ganglia,    148.      See    also    Nervous   sys- 
tem. 
Gastric  glands,  354.    See  also  Digestive 

system. 

Gigantism,  573 
Gilson's   fluid    for    fixation    of    tissues, 

730 
Glands,  253 

accessory  lacrimal,  of  Krause,  677 
adrenal,  548 

lymphatics  and  nerves  of,  556 
anterior  lingual  (of  Nuhn),  342 
branched  saccular,  260 
branched  tubular,  258 
bulbo-urethral,  501 
cardiac,  of  stomach,  360 
carotid,  569 
ceruminous,  of  ear,  684 
ciliary,  of  eye,  640 
cervical,  of  uterus,  632 
classification  of,  253 


INDEX 


835 


Glands,  eoccygeal,  570 
compound   saccular,  260 
compound  tubular,  258 
compound  tubulo-alveolar,  258 
convoluted  tubular,  257 
Cowper's,  of  urethra,  501 
ductless,   260-548 

hormones  of,  586 
duodenal    (Brunner's),   365-372 
endocrin,  260-548 

hormones  of,  586 
histologic  types  of,  254 
internal  secretion  of,  261 
intestinal     (crypts    of    Lieberkuhn), 

366 

of  small  intestine,  370 
lacrimal,  679 

lenticular,  of  stomach,  360 
mammary,  541 

active,  543-545 

blood  vessels  of,  547 

milk,  547 

of  Montgomery   (areolar  glands  of 

Duval),  545 
Marchand's     (Marchand's    adrenal), 

557 

Meibomian  (tarsal),  of  eyelid,  676 
mucous,  255 
mucus  of,  256 
of  Bartholin    (Bartholin's  glands  of 

vulva),  541 
of  esophagus,  351 
of  eyelid  (glands  of  Moll),  676 
•f  Harder,  681 
of  tongue,  342 
of  Tyson,  of  penis,  506 
of  von  Ebner,  343 
of  Zeiss,  of  eyelid,  676 
parathyroid,  acidophil  cells  of,  564 

blood  supply  of,  565 

structure  of,  562 
parotid,  390 

physiologic  types  of,  254 
pineal,  579 

posterior  tarsal,  of  Waldeyer,  677 
preputial,  506 
prostate,  497 


Glands,  pyloric,  357 
racemose,  258 
secreting,  of  mouth,  321 
suprarenal,  548 

chromaffin  granules  in,  554-555 
development      and      function      of, 

548 

lymphatics  and  nerves  of,  556 
medulla,  cells  of,  553 
zona  glomerulosa  of,  552 
zona  reticularis  of,  553 
zona  fasciculata  of, '552 
salivary,  382 

serum- secreting  cells  of,  256 
simple  saccular,  259 
simple  tubular,  257 
submaxillary,  391 
thymus,    565-567 
thyroid,  blood  supply  of,  560 
colloid  in,  557 
development  of,  561 
follicles  of,  557 
follicular   epithelium   of,   559 
function  of,   561 
lymphatics  of,  560 
nerves  of,  561 
structure  of,  557 
urethral  (Littre's),  454 
uterine,  531 
Glandulae  vestibularis,  majores   (glands 

of   Bartholin),   541 
minores  of  vulva,  541 
Glandular  epithelium,  40 
Glaucoma,  635 
Glia  cells,  141 
Glomus  caroticum,  569 
Glomus  coccygeum,  570 
Glycerin  jelly,   for   mounting  sections, 

760 
Glycogen,    Gage's    method    for    demon 

strating,  758 
Goblet  cell  epithelium,  41 
Goitre,  561 

exophthalmic,  561 

Gold  chlorid  for  demonstrating  nerve 
plexuses  and  nerve  endings 
(Ranvier's  method),  752 


836 


INDEX 


Golgi's  cells  of  cerebral  cortex,  types 

1  and  2,  613 

Golgi's  stain  for  nerve  cells,  751 
Graafian  follicle,  517 
Graafian  follicle,  Resume  of  structures, 

519 

Graves'  disease,  561 
Guard  cells,  38 
Gum-damar,  for  mounting  sections,  760 

Hair,  277 

development  of,  277 

regeneration  of,  286 

root  of,  281 

root  sheaths  of,  283 

shaft  of,  281 

structure  of,  277 
Haploid     group     of     chromosomes     in 

spermatogenesis,  464 
Hardening  of  tissues,  733 
Basting's   method   for   blood    (eosinate 
of  methylene  blue  stain),  754 
Haversian  spaces  in  bone,  84 
Haversian  systems  of  bone,  75-84 
Heart,  195 

annulus  fibrosus  of,  197 

atrioventricular  bundle  of,  199 

blood  vessels  of,  201 

chordae  tendinea?  of,  197 

columnae  carnae  of,  198 

development  of,  201 

endocardium  of,  196 

endomysium  of,  195 

epicardium  of,  195 

moderator  bands  of,  199 

myocardium  of,  195 

nerve  supply  of,  202 

valves  of,  196 

venae  minimae  of,    201 
Heat,  fixation  of  tissues  by,  730 
Kelly's  fluid  for  fixation  of  tissues,  728 
Hemal  nodes,  239 
Hematein,  for  staining  tissues,  741 

stains,  application  of.  743 

and  eosin  stains  for  tissues,  746 
Hemoglobin,  211 
Hemolymph  nodes,  239 


Hemopoiesis,   214 

Heterozygotc,   478 

Histogenesis,   1-27 

Histologic  technic,  720 
bibliography  of,  761 

Histology,  definition  of,  1 
historical  development  of,  2 
relations  o'f,   to  other  biological  sci- 
ences,  2 

Homozygote,  478 

Hone  for  microtome  knife,  737 

Howship,  lacunas  of,  84 

Hyaline  cartilage,  68 

Hyaloid  artery,  of  eye,  672 

Hyaloid  membrane,  of  eye,  669 

Hyaloplasm,  8 

Hydatid  of  Morgagni,  539 

Hymen,  541 

Hypopituitarism,  573 

Hypophysis  cerebri,  572-573-574-575 
function  of,  573 

histologic  structure  of,  573-574-575 
pars  buccalis  seu  glandularis,  575 
pars  neuralis;   infundibulum,   575 
parts  of,  575 
Eathke's  pouch,  572 

Ileocecal  (colic)  valve,  379 
Incus,  of  ear,  689 
Injection  of  tissues,  732 

pressure  required  for,  how  obtained, 

733 

with  Berlin  blue  gelatin  mass,  732 
with  carmin  gelatin  mass,  732 
Intercalated  discs  of  cardiac  muscle,  99 
Internal  ear,  acoustic  nerve,  702 
aqueductus  vestibuli  of,  694 
auditory  artery  of,  714 
blood  supply  of,  714 
bony  labyrinth  of,  694 
canalis  communis  of,  699 
cecum  vestibulare  of  scala  media,  703 
cochlea,  accessory  tectorial  membrane 

of,  706 

basilar  membrane  of,  706 
function  of,  716 
foramina  nervosa  of,  702 


INDEX 


837 


Internal     ear,     cochlea,     hamulus     of, 
701 

helicotrema  of,  703 

Hensen's  stripe  of  tectorial  mem- 
brane, 706 

limbus  spiralis  of,  705 

membrana  tectoria    (membrane  of 
Corti)   of,  703-705 

membranous  wall  of  scala  tympani 
and  scala  vestibuli,  704 

organ  of  Corti,  cells  of,  708-709 

prominentia  spiralis  of,  705 

spiral  ligament  of,  704 

structure  of,  701 

sulcus  spiralis  externus  of,  705 

sulcus  spiralis  internus  of,   703 

vestibular     membrane     (of     Reiss- 

ner),  704 

cochlear  artery,   714 
cochlear   nerve,    spiral    ganglion    of, 

712 

ductus  endolymphaticus  of,  694 
endolymph  of,  695 
endolymphatic  sac  of,  694 
fenestra  vestibuli  of,  693 
general  considerations  of,  693 
helicotrema,  703 
internal  auditory  vein,  716 
lagena   or   cecum    cupulare    of    scala 

media,  703 
lymphatics  of,  716 
macula  acustica  sacculi,  697 
macula  acustica  utriculi,  698 
membranous  labyrinth  of,  694 
neuro-epithelium,  of  saccule,  695 

varieties  of,  697-708-709 
organ  of  equilibration,  700 
otocyst,  699 
otoliths  in,  697 
perilymph  of,  695 
saccule  of,  695 
sacculus  of  vestibule,  694 
scala  media  or  cochlear  duct  of,  703 
scala  tympani  of  cochlea,  701 
scala  vestibuli  of  cochlea,  701 
secondary     tympanic     membrane     of 
cochlea,  703 


Internal    ear,    semicircular   canals    of, 

699 

ampullae  of,  699 
spiral  organ  of  Corti,  702 
utricle  of,  698 
utriculosaccular    canal    of    vestibule, 

694 

utriculus  of  vestibule,  694 
veins  of,  715-716 
vestibular  artery,  714 
vestibular  ganglion  (of  Scarpa),  712 
vestibular   membrane    (of  Eeissner), 

702 

vestibule  of,  693 

Internal  genital  organs,  female,  507. 
See  also  Reproductive  sys- 
tem. 

Interrenal  bodies,  548 
Interstitial  granules  of  Kolliker,  99 
Interfilar  mass,  8 
Intestine,  large,  377 

appendices  epiploicae  of,  377 
lymphoid  tissue  and  lymph  nodes  of, 

378 

mucous  membrane  of,  377 
plicae  semilunares  of,  377 
rectum,  379 

sacculations  or  haustra  of,  377 
tseniae  coli  (lineae  coli),  377 
vascular  and  nerve  supply  of,  379 
vermiform  appendix  of,  378 
Intestine,      small,      absorption      from, 

375 

acidophil  cells  of,  371 
agminate       nodules       of       (Peyer's 

patches),  366 
blood  supply  of,  373 
chromaffin  cells  of,  371 
chyle  in,  374 
corium  of,  366 
duodenal    glands   '(Brunner's),    365- 

372 

glands  of,  370 
glands    (crypts    of    Lieberkiihn)    of, 

366 

granule  cells  of  Paneth,  370-371 
lacteals  of,  369 


838 


INDEX 


Intestine,    small,   lining   epithelium   of, 
369 

lymphatics  of,  371 

mucous  membrane  of,  366 

my  enteric    ganglionic    plexus    (Auer- 
bach's),  375 

nerve  supply  of,  374 

Fever's  patches  of,  366 

solitary  nodules  of,  366 

structure  of,  363 

submucosa  of,  364 

submucous  plexus  (Meissner's),  375 

valvulae  conniventes  of,  364 

villi  of,  366-368 

Intracartilaginous  ossification,   79 
Intra   vitam   method   of    staining   non- 
medullated  nerve  fibers  with 
methylene  blue,  749 
Iridocorneal  angle,  643 
Iris,  641 

circulus  major  of,  672 

circulus  minor  of,  673 

color  of,  642 

dilator  muscle  of,  642 

endothelium  of,  641 

fibrous  stroma  of,  642 

internal  epithelium  of,  643 

layers  of,  641 

sphincter  muscle  of,  642 
Iron  hematoxylin,  for  staining  tissues, 
747 

Joints,  88 

adaptation  cartilages  of,  89 
diarthroses,  88 
intra-articular  menisci,  88 
labra  glenoidalia,  89 
sutura,  88 
synarthroses,  88 
synchondroses,  88 
syndesmoses,  88 
synovia,  89 
synovial  membrane,  89 

Karyon,  18 
Keratin,  45 
Kidney,  423 


Kidney,    arched    collecting    tubule    ol 
(junctional  tubule),  437 

arciform  arteries  of,  440 

arciform  veins  of,  443 

arteries,  interlobular,  of,  441 

arteriolae  rectse  of,  441 

ascending  limb  of  Henle's  loop,  435 

Bellini's  duct  of,  438 

blood  vessels,  lymphatics  and  nerves 
of,  440 

capsule  of  Bowman,  429 

corpuscles  in,  425 

cortex  of,  424 

descending    limb    of   Henle's   tubule, 
434 

distal   convoluted    portion    of    tubule 
in,  436 

divisions  of  the  renal  tubule,  429 

glomerulus  of,  429 

loop  of  Henle,  435 

lymphatics  and  nerves  of,  444 

medulla  of,  424 

neck  of  tubule  of,  431 

papillary  ducts  of,  438 

proximal    convoluted    portion    of    tu- 
bule of,  431 

renal  connective  tissue,  426 

renal  corpuscles    (Malpighian  body), 
425-429 

renal  lobule,  426 

renal  pelvis  and  ureter,  44o 

blood      supply,      lymphatics      and 

nerves  of,  448 
mucosa  of,  445 
muscular  coat  of,  448 
tunica  propria  of,  447 

straight  collecting  tubules  of,  437 

table  of  divisions  of  renal  tubule,  439 

table  showing  the  course  of  the  renal 
circulation,  443 

topography  of,  423 

tubules,  peculiarities  of,  440 

uriniferous,  or  renal  tubules  of,  427 

venae  propriae  renales,  443 

veins,  stellate  of,  443 
Kleinenburg 's  fluid,  for  fixation  of  tis- 
sues, 729 


INDEX 


Knife,  microtome,  hone  for,  737 
Kb'lliker's  muscle  columns,  112 
venulae  of,  443 

Labia  majora,  of  pudendum,  540 

Labia  minora,  of  pudendum,  540 

Lacrimal  gland,  679 

Lacrimal  lake,  679 

Lacteals,  of  small  intestine,  369-374 

Lactiferous   duct,    of   mammary   gland, 

542 

Lamellae,    external    circumferential,    of 
bone,  84 

internal     circumferential,     of     bone, 
85 

interstitial,  of  bone,  85 
Larynx,    300 

structures  of,  300 

vocal  cords  of,  301 
Lenticular  glands,  of  stomach,  360 
Ligamentum    denticulatum,    of     spinal 

cord,  621-624 

Ligamentum  pectinatum,  of  eye,  643 
Ligaments,  117 

circular  dental,  329 
Lingual  glands,  anterior,  342 
Lingual  tonsil,  244-343 
Littre's  glands,  urethra],  454 
Liver,  405 

bile  capillaries  of,  411 

blood  supply  of,  417 

capsule  of  Glisson,  408 

cells  of,  412 

connective  tissue  of,  408 

course  of  blood  through,  419 

interlobular    arteries    and    veins    in, 
415 

interlobular  bile  ducts  of,  415 

lobule  of,  409 

lymphatics  of,  419 

nerves  of,   420 

pigment  in,  414 

portal  canals  of,  408-415 

portal  vein  of,  417 

structure  of,  405 

Loose  spireme,  of  cell  nucleus,  24 
Lumbar  region,  of  spinal  cord,  600 


Lung,  304 
atria  of,  310 
blood  supply  of,  314 
lobule  of,  314 
lymphatics  of,  318 
nerve  supply  of,  319 
pulmonary  alveoli  of,  311 
tissue  fixation  of,  730 
Lutein  cells,  of  ovary,  519 
Lymphatic  system,  225 

amygdala   (faucial  tonsils),  242 

bursae,  233 

cisterna  chyli,  230 

chyle,  226 

hemolymph,  or  hemal  nodes,  239 

lymph,  225 

lymph  cells,  235-238 

lymph  corpuscles,  225 

lymph  follicles,  233 

lymph  glands,  235 

lymph  nodes,  235 

blood  vessels  of,  239 

development  of,  242 

structure  of,  236 
lymph  nodules,  233 
lymph  sinus,  236 

lymph  vessels,  development  of,  230 
lymphatic  capillaries,  227 
lymphatic  vessels,  226 
lymphatics,  of  adrenal  gland,  556 

of  bone,  78 

of  eye,  673 

of  eyelid,  678 

of  internal  ear,  716 

of  kidney,  444 

of  large  intestine,  378 

of  liver,  419 

of  lung,  318 

of  mammary  gland,  547 

of  middle  ear,  693 

of  penis,  506 

of  salivary  glands,  393 

of  small  intestine,  374 

of  stomach,  362 

of  thyroid  gland,  560 

of  tongue,  344 
lymphoid  tissue,  64 


840 


INDEX 


Lymphatic         system,         marrowlymph 

glands,  240 
spleen,  245 

blood  vessels  of,  246 

development  of,  250 

differentiation      of,      from      lymph 
node,  249 

functions  of,  249 

pulp  veins  of,  248 
splenic  cells,  249 

splenic      nodule      (Malpighian      cor- 
puscle), 247 
splenolymph  glands,  240 
thoracic  duct,  230 
tonsils,  faucial,  242 

lingual,  244 

palatine,  242 

pharyngeal,   244 

salivary  corpuscles  of,  243 

tubal  tonsil  (of  Gerlach),  692 

Malleus,  of  ear,  689 

ligaments  of,  691 
Mallory's      connective      tissue      stain, 

753 
Mammary  glands,  541 

active  gland,  543 

blood  vessels  of,  547 

circulus  venosus  of  Haller,  of,  547 

colostrum,  546 

lactiferous  duct  of,  542 

lymphatics  and  nerves  of,  547 

milk,  547 

resting  gland,  545 

Mann's      acid      hematein       (Ehrlich's 
Hematoxylin)   stain,  for  tis- 
-  sues,  742 

Marehand's   glands    (Marchand's  adre- 
nal), 557 

Marginal  velum,  590 
Marrow,  of  bone,  77 

blood  supply  of,  78 

cavities,  primordial,  in,  82 

primary  osteogenic,  82 

red,  77 

Mastoid  cells,  of  ear,  686 
Maturation,  of  germ  cells,  460 


Mayer 's  albumin,  for  fastening  sections 

to  slide,  739 
Medullary  sheath,  134 
Meibomian  glands,  of  eyelid,  676 
Meissner's  submucous  plexus,   347 
Membrana  propria,  34 
Membrane,   mucous,  of  large  intestine, 

377 

mucous,  of  small  intestine,  366 
mucous,  of  mouth,  320 
synovial,  89 
Membranous  labyrinth,  of  internal  ear, 

604 

Meninges    and    blood    supply    of    cere- 
brum, 619-620-621 
Mendelism,  477 

Mercuric    chlorid,    for    fixation    of    tis- 
sues, 725 
Mercuro-nitric  mixture,  for  fixation  of 

tissues,  730 
Mesenchyma,  50 
Mesoderm,  28 
Mesothelium,  37 
Mesovarium,  507 
Metabolism,  14 

Metaphase,  of  mitotic  cell  division,  25 
Methyl    blue    and    safranin    stain,    for 

tissues,   747 

Methyl  green  stain,  for  tissues,  743 
Methylene       blue,       for      chromophilic 
(tigroid)    granules  in  cyton 
and  dendrons,  750 
stain  for  non-medullated  nerve  fibers 

(intra  vitam  method),  749 
tissue  stain,  743 

Meves'  method  for  staining  mitochon- 
dria, 757 

Microtome,   for   sectioning   tissues,   736 
Microtome    knife,    for    sectioning    tis- 
sues, 737 
hone  for,  737 
use  of  strop  for,  738 
Middle  ear,  685 

blood  vessels  of,  693 
general  considerations  of,  685 
lymphatics  of,  693 
Milk,  547 


INDEX 


841 


Mitochondria,   8-50 

Mitochondria!  technics,  Meves'  method, 
757 

Benda's  method,  757 
Mitome,  8 
Mitosis,  22 

Montgomery's  glands,  of  mamma;,  545 
Molecular  motility,  17 
Monaster  stage  of  mitotic  cell  division, 

25 

Mordants,  for  dyes,  741 
Morphogenesis,  29 

Motor  area,  of  cerebral  cortex,  615 
Mounting  sections,  759 

euparal  for,  761 

glycerin  jelly  for,  760 

gum-damar  for,  760 

neutral  balsam  for,  760 

xylo-balsam  for,  760 
Mouth,  320 

lymphoid  tissue  of,  321 

mucous  membrane  of,  320 

secreting  glands  of,  321 
Muchematin   stain,   for   tissues,    748 
Mucicarmin  stain,  for  tissues,  748 
Mucous  membranes,  251 

of  alimentary  canal,  347 

of  mouth,  320 

structure  of,  251 
Mucous  tissue,  54 
Mucus,  256 

formation  of,  41 
Muller's  fibers,  of  retina,  658 
Miiller's   solution,    for   fixation   of   tis- 
sues, 726 

Miillerian  ducts,  456 
Muscse  volitantes,  669 
Muscle,  striped,  112 

areas  of  Cohnheim,  112 

as  a  whole,  112 

blood  supply  of,  114 

cardiac  (involuntary  striped), 90-94, 99 
atrio-ventricular  bundle  of  His,  102 
intercalated  discs  in,  99,  104 
intercalated    discs    (Zimmermann's 
technic   for   demonstrating), 
758 


Muscle,     cardiac,     nerve     endings     in, 

175 

Purkinje  fibers  of,  102 
contraction  bands  of,  93 
endomysium  of,  112 
epimysium  of,  112 
fasciculus  of,   112 
histogenesis  and  structure  of,  91 
inokommata  of,  98-104 
interstitial  granules  of  Kolliker,  99 
Kolliker 's  columns,  112 
mesophragma  of,  98 
myoblasts,   90 
myofibrils,  90 
myochondria  of,  92 
myofibrils  of,  104 
myoglia  of,  93 
myotomes,  106 

nerve  endings  in,  114-115,  171,  175 
of  heart,  94-99 
perimysium  of,  112 
red,  110 

sarcolemma  of,  92 
sarcomeres  of,  98-104 
sarcoplasm  of,  90 
sarcosomes,  of  Retzius,  99 
sarcostyle  of,  104 
skeletal,  90 
smooth   (involuntary;   unstriped),  90, 

91 

histogenesis,   and   structure   of,   91 
myofibrils,  93 
nerve  endings  in,  175 
situation  of,  94 

structure   of  border  fibrils   (myog- 
lia) in,  93 
telopragma  of,  98 
types  of,  90 
unstriped,  90 
voluntary  striped,  104 

(skeletal),  90 
Muscle  spindles,  172 
Muscular  contraction,  111 
Myelospongium,    of    developing    spinal 

cord,  509 

Myenteric  plexus,   and  ganglion,   346 
Myoblasts,  90 


842 


INDEX 


Myocardium,  195 
Myofibrils,  90 
Myxedema,  561 

Nabothian  follicles,  of  uterus,  532 
Nails,  274 

structure  of,  275 
Nasal  cavity,  293 

4Hood  vessels  of,  298 

neuro-epithelium  of,  297 

olfactory  portion  of,  296 

respiratory  portion  of,  294 

vestibule  of,  293 

vomero-nasal  organ  of  Jacobson,  295 
Nasopharynx,  299 
Nerve  cell,  121 

apyknomorphous  condition  of,   124^ 

association  neurons,  131 

axis  cylinder  process  of,  128 

axon,  125 

axon  hillock,  129 

axoplasm,  129 

cellulifugal  process  of,  130 

chromophilic  substance  of,  123 

collaterals  of,  129 

commissural  neurons,  131 

cytochromatin  of,  123 

cytoplasm  of,   121 

dendrons  (dendrites)   of,  127-128 

end  arborization  of,  129 

ganglia,   148 

Golgi's  cells,  type  1  (Deiter's  cells), 

131 
type  2,  131 

implantation  cone  of,  129 

mitochondria  in,  125 

neuraxis,  128 

neuraxon,   128 

neurite,  128 

neuro-epithelium,  42 

neurons,  125 

Nissl's  substance  of,  123 

nucleus  of,  121 

origin  of,  131 

processes  of,  127 

projection  neurons,  131 

protoplasmic  processes  of,  128 


Xerve  cell,  pyknomorphous  condition  of, 
123 

size  of,  131 

spinal  ganglia,  150 

telodendrion  of,   129 

tigroid  substance  of,  123 
Nerve  endings,  159 

circurngemmal   fibers   in    taste   buds, 
163 

in  connective  tissue,  163 

corpuscles  of  Grandry,  169 

corpuscles  of  Herbst,  169 

end  bulbs  of  Krause,  174 

end  fibrils,  159 

epicritic  sensibility  of,  164 

epithelial  cells  in,  159 

genital  corpuscle,  166 

Golgi  end  organs,  174 

Golgi-Mazzoni  corpuscles,  169 

gustatory  cells,  161 

gustatory  organs,  160 

intergemmal  fibers,  163 

intragemmal  fibers,  163 

Key-Eetzius  corpuscles,  169 

lamellar   (Pacinian.)   corpuscles,   167 

Merkel's  corpuscles,  169 

motor  end  plates,  171 

muscular,  171 

muscle  spindles,  172 

neuro-epithelium,  160 

neuromuscular  end  organs,  171 

neuromuscular  spindles,   172 

neurotendinous  end   organs,   174 

Pacinian  corpuscles,  167-174 

peripheral  end  organs,  159 

protopathic  sensibility  of,  164 

Rufnni's  end  organs,  165 

sole  plate,  172 

sustentacular  cells,  161 

tactile  cells,  159 

tactile  corpuscles,  163 

tactile  meniscus,  160 

taste  buds  in,  160 

tendon  in,  171 

tendon  spindles,  174 

terminal  cylinders,  165 

touch  corpuscles  of  Meissner,  ]6S 


INDEX 


843 


Xerve  endings,   trefoil  plates,   159 

Yater's  corpuscles,  167 

Vater-Pacinian  corpuscles,  167 
Xerve  fibers,  132 

axis  cylinder  of,  132 

axolemma  of  Kiihne,  134 

axon  fibrils,  134 

axoplasm  of,  134 

endoneurium  of,  132-147 

fiber  bundles,  139 

funiculi  of,  139 

glia  fibers,  144 

incisures  of  Schmidt,  135 

internodal  segments  of,  135 

medullary  segments  of,  136 

medullary  sheath  of,  132-134 

medullated,  132 

•with  a  neurolemma,  132 
without  a  neurolemma,  137 

myelin  of,  135 
sheath  of,  132-134 

neuroglia,  occurrence  of,  in,  145 

neurolemma  of,  136 

neurokeratin  of,  135 

neuroplasm  of,  134 

nodes  of  Ranvier,  132 

non-medullated,  132 

with  a  neurolemma,  137 
without  a  neurolemma,  137 

nucleated  sheath  of  Schwann  of,  136 

Kemak's  fibers,   137 

Schmidt-Lantermann  lines  in,  135 

sheath  cells  of,  137 

sheath  of  Henle,  132-147 

sympathetic  nerve  fibers,  137 

telodendrions  of,  140 

terminal  arborizations  of,  140 

tracts,  139 

trophic  center  of  neuron,  137 

ultimate  fibrillae  of,  133 

Wallerian  degeneration  of,  140 

white    substance    of    Schwann,    132- 

134 
Xerve  trunks,  funiculus  of,  146 

lymphatic  vessels  of,  147 

nervi  nervorum,  148 

nervi  erigentes,  of  penis,  506 


Xerve  trunks,  perineurium  of,  146 
structure  of,  146 
vascular  supply  of,  147 
Xervous  system,  587 
blood  supply  of,  624 
cerebellum,   603 

basket  cells  of,  608 
climbing  fibers  of  medulla,  609 
cortex  of,  606 
granule  cells  of,  609 
large  stellate  cells  of,  609 
medulla  of,  609 
Purkinje  cells  of,  607 
resume  of  structures  of,  611 
small  cortical  cells  of,  608 
cerebral  cortex,  611 

arteries  of,  circle  of  Willis,  624 
cortical,  625 
fissural,  625 
medullary,  625 
middle  cerebral,  625 
terminal,  625 

auditory  area  of,  cells  of,  618 
cell  layers  of,  612 
cells,  Betz,  of,  613-616 
giant  pyramidal,  613 
Golgi's,  types  1  and  2,  613 
solitary,  of  Meynert,  613 
frontal  lobe  of,  617 
granule  cell  layer  of,  617 
inner  large  pyramidal  cell  layer  of, 

617 
inner   polymorphous   cell  layer   of, 

617 

molecular  layer  of,  617 
occipital  lobe  of,  617 
outer  large  pyramidal  cell  layer  of, 

617 
outer   polymorphous   cell  layer  of, 

617 

outer  stripe  of  Baillarger,  619 
parietal  lobe  of,  617 
radial  fibers  of,  618 
small  pyramidal  cell  layer  of,  617 
temporal  lobe  of,  617 
thickness  of,  612 
visual  area  of,  617 


844 


INDEX 


Nervous  system,  cerebrum,  611 

and     spinal    cord,     meninges     and 

blood  supply  of,  619 
basal  ganglia  of,  611 
corpus  callosum,  611 
gyri  of,  611 
hemispheres  of,   611 
insula  of,  612,  617 
medulla  of,  611 
occipital  lobe  of,  611 
pallium  of,  611 
parietal  lobe  of,  611 
sulci  of,  611 
Sylvian  fissure  of,  612 
temporal  lobe  of,  612 
veins  of,  625 
development,  587-595 
of  cardie  plexus,  591 
of  ependyma  cells,  589 
of  marginal  velum,  590 
of  myelospongium,  589 
of       neural       groove       (medullary 

groove),  587 

of  neural  or  ganglionic  crest,  587 
of  neural  plate,  587 
of  neural  tube,  587 

derivatives  of,  594 
of  neuroblasts,  589 
of  neuroglia  cells,  589 
of  neurons,  587 
of  spongioblasts,  589 
of  sympathetic  plexus,  591 
meninges,  620 
arachnoid,  620 

granulations  of,  621 

Pacchionian  bodies  of,  621 

subarachnoid  space,  621 

villi  of,  621 
dura  mater,  620 

epidural  space  of,  620-623 

subdural  space  of,  620 
pia  mater,  622 

choroid  plexus  of,  623 

telse  choroideae  of,  623 
motor     area     of     cerebral     cortex, 

615     . 
cells  of  Martinotti,  617 


Nervous   system,   inner   polymorphous 

cell  layer  of,  616 
layers  of,  615 
marginal  velum,  615 
molecular  layer,  615 
outer     polymorphous     cell     layer, 

615 
outer  polymorphous  cell  layer  of, 

618 

outer  stripe  of  Baillarger  of,  618 
pyramidal  cell  layer,  616 
small  pyramidal  cell  layer,  615 
small    pyramidal    cell    layer    of, 

618 
solitary     cells     of     Meynert     of, 

618 

stratum  zonale,  615 
stripe  of  Bechterew  of,  619 
supraradial  felt  work,  619 
tangential  fiber  layer,  619 
spinal  cord,  596 

anterior  spinal  artery  of,  624 

basis  cornu,  596 

caput  cornu,  596 

cell  column  of  Clarke,  600 

central  canal  of,  598 

central  commissure,  596 

cervical  region,  lower  half,  602 

upper  half,  613 
cervix  cornu,  596 
columns  of,  598 
conus  medullaris,  600 
filum  terminale,   600 
gray  matter  of,  596 
intermediate  zone  of,  596 
ligamentum    denticulatum,    621 
lumbar  region  of,  601 
nerve  roots  of,  596 
nucleus  of  Stilling,  602 
regions  of,  599 
sacral  region  of,  600 
segments  of,  596 
septum  posticum,  621 
structure  of,  596 
thoracic  region  of,  607 
veins  of,  625 
white  matter  of,  598 


INDEX 


845 


Nervous    system,    sympathetic    division 

of  nervous  system,  153 
cranial  autonomic,  153 
sacral  autonomic,  153 
sympathetic  ganglia,  154 
sympathetic   proper,   153 
tissues  of  nervous  system,  119 
axon,  119 
cell  body,  119-121 
cyton,   121 
dendrites,  119 
dendrons,  119 
epineurium  of,  146 
ganglion,  121 
ganglion  cell,  121 

glomerulus  of,  152 
general  considerations  of,   119 
nerve  fiber,  119 
neuroglia  (glia  tissue),  121 

astrocytes   (neuroglia  cells),  141 
long  rayed  or  spider  cells,  143 
short  rayed  or  mossy  cells,  143 
ependyma,  141 
neuron,  119 
neurone  theory,  157 
perikaryon,  121 
stains  of,  748 

Cajal's   method   for   demonstrat- 
ing nerve  fibrils,   750 
gold   chlorid,   Ranvier's   method, 
for  nerve  plexuses  and  nerve 
endings,  752 
Golgi's,  751 

methylene   blue,   for    non-medul- 
la ted     nerve     fibers     (intra 
vitam  method),  749 
Nissl's      method      for      staining 
chromophilic  (tigroid)  gran- 
ules  in   cyton   and   dendron 
with  methylene  blue,  750 
Weigert's,  for  medullated  nerve 

fibers,  748 
Neurone  theory,  157 
Neutral  balsam,  for  mounting  sections, 

760 

Neutral  dyes,  740 
Normal  salt  solution,  720 


Nucleus,  basic  chromatin  of,  6 
chromatin,  6 
chromatin  nucleoli,  6 
chromioles,   6 
karyolymph,  6 
karyoplasm,  6 
karyosomes,  6 
linin,  6 

net  knots  in,  6 
nucleoplasm,  6 
nuclear  sap,  6 
oxychromatin  of,  6 
paralinin,  6 
plasmosomes,  6 

Ocular  conjunctiva,  674 

Ocular  contents,  665 

Odontoblasts,  324 

Odontoclasts,  337 

Olfactory  area,  of  cerebral  cortex,  618 

Ob'genesis,  460-478 

oogonia,  in  ovary,  512 

ootid,  or  mature  ovum,  479 

primary  oocyte,  478 

polar  body,  479 

secondary  oocyte,  479 
Optic  cup,  645 
Optic  nerve,  664 
Optic  stalk,  645 
Optic  vesicle,  645 
Optical  axis,  of  eye,  628 
Ora  serrata  of  eye,  665 
Orange  G.  tissue  stain,  746 
Organ,  of  Corti,  of  ear,  708-709 

of  equilibration,  700 

of  hearing,  716 

of  Jacobson,  295 

of  Rosenmiiller,  539 

Orth's  fluid,  for  fixation  of  tissues,  727 
Osmic  acid  stain,  for  fat,  758 
Ossification,  centers  of,  79 

endochondral,  85 

epiphyseal,  85 

intramembranous,  86 

intracartilaginous,  79 

perichondrial,   84 
Osteoblasts,  77-83 


846 


INDEX 


Osteoclasts,  78 
Otoliths,  697 
Ovarian  follicle,  518 

atresia  of,  514 

corona  radiata  of,  518 

cumulus  ob'phorus,  518 

development  of,  513 

discus  proligerus,  517 

liquor  folliculi,  514 

Pfliiger's  tubes,  513 

resume  of  structures,  519 

stigma  of,  518 

stratum  granulosum,  517 

vesicular,  or  Graafian  follicle,  517 
Ovarian  scars,  522 
Ovary,  507 

blood  supply  of,  522 

corpora  albicantia,  of,  510-521 

corpora  lutea  of,  509 
spuria,  521 
vera,  of  pregnancy,  521 

corpus  hemorrhagicum,  519 

corpus  luteum,  507-519 

cortex  of,  508 

•hiium  of,  508 

lutein  cells  of,  519 

lymphatics  of,  525 

medulla  of,  508 

nerves  of,  525 

ova,  510 

ovarian  follicles,  509 

pampiniform  plexus  of,  523 

plexus  venosus  of,  523 

primitive  follicles  of  (egg  nests),  514 

tunica  albuginea  of,  510 
Oviduct,  blood  supply  of,  527 

lymphatics  and  nerves  of,  528 

mucosa  of,  526 

muscular  wall  of,  526 

structure  of,  525 
Ovum,  the,  511 

accessory  nucleus  of,  511 

cytoplasm  of,  511 

deutoplasm  of,  511 

nuclear  cap  of,  511 

nucleus  or  germinal  vesicle  of,  511- 
512 


Ovum,  the,  ob'cytes,  512 

ootid,  512 

vitelline  membrane  of,  511 

vitellus,  511 

yolk  nucleus  of,  511 

zona  pellucida  of,  511 
Oxyhemoglobin,  211 

Pacchionian  bodies,  621 
Pacinian  corpuscles,   174 
Palpebral  conjunctiva,  674 
Palpebral  muscle,  of  Miiller,  677 
Pampiniform  plexus,  of  ovary,  523 

of  spermatic  cord,  494 
Pancreas,  394 

centro-acinal  cells,  of  Langerhans,  of; 
396 

general  considerations  of,  394 

islands   of   Langerhans,   399 

nerve  supply  of,  404 

pancreatic  islets,  399 

resume  of,  404 
Papillae,  circumvallate,  of  tongue,  341 

conical,  of  tongue,  340 

filiform,  340 

foliate,  of  tongue,  341 

fungiform,  of  tongue,  340 

lenticular,  of  tongue,  342 
Paradidymis,  organ  of  Giraldes,  502 
Paraffin,     embedding     of     tissues     in, 

735 

Paraganglia,  571 
Paraganglion  caroticum,  570 
Parahypophysis,  578 
Paramitone,  8 
Paraplasm,  8 
Parasynapis,  463 
Parathyroid  gland,  562 

acidophil  cells  of,  564 

blood  supply  of,  565 

structure  of,  562 
Parietal  lobe,  of  brain,  617 
Paroophoron,  540 
Parovarium,  539 
Parotid  gland,  390 

Stenson's  duct  of,  390 
Pectinate  ligament,  of  eye,  635 


INDEX 


847 


Penis,  503 

corpus   cavernosum,   pectiniform   sep- 
tum of,  504 

corpus  spongiosum  of,  503-506 

glands  of  Tyson  of,  506 

helicine  arteries  of,  504 

lymphatics  of,  506 

nerves  of,  506 

nervi  erigentes  of,  506 

preputial  glands  of,  506 

tunica  albuginea  of,  504 
Peptic  glands,  354 

or    adelomorphous    glands,    of    stom- 
ach, 355 

Pericementum,  of  teeth,  329 
Perichondrial  ossification,  84 
Perichondrium,  72 
Periodontium,  329 
Periosteum,  74 
Peyer's  patches,  366 
Pharyngeal  tonsil,  244 
Pharynx,  347 

Pheochrome  cells,  of  adrenal,  548 
Pheocrome  organs,  571 
Pia  mater,  622 

Picrocarmin  stain,  for  tissues,  744 
Picro-fuchsin  (Van  Gieson's)  stain,  for 

connective  tissue,  752 
Pigment  cells,  52 

Pineal  body  (conarium;  epiphysis  cere- 
bri),  579 

blood  supply  of,  584 

development  of,  580 

function  of,  581 

habenular  commissure  of,  581 

posterior  commissure  of,  584 

structure  of,  582 
Pineal  eye,  580 
Pineal  recess,  580 
Pineal  stalk,  580 
Pinna,  682 
Pituitrin,  573 
Pituitary  body,  572 

pars  buccalis  of,  575 

pars  neuralis  of,  575 

Kathke's  pouch,  572 

structure   of,   573-575 


Placenta,  536 

Pleura,  312 

Pleural  pores,  313 

Polarity,  of  cells,  39 

Portal  vein,  417 

Posterior  chamber  of  eye,  636-643 

Potassium   bichromate,   for   fixation   of 

tissues,  726 
Preputial  glands,  506 
Prickle  cells,  44 
Prophase,  24 
Prostate  gland,  497 

blood  supply  of,  500 

concretions  of,  corpora  amylacea,  499 

structure  of,  497 
Protopathic  sensibility,  164 
Protoplasm,  1 

alveolar,  13 

ameboid  motility  of,  16 

chemical  constitution  of,  2 

ciliary  motility,  16 

circulatory  movement  of,  17 

colloidal  biogens  of,  10 

colloids,  4 

contractility  of,   15 

crystalloids,  4 

emulsoid  of,  14 

gel  state  of,  4 

granular,  13 

irritability   of,   15 

metabolism  of,  14 

molecular  motility  of,  17 

muscular  movement,  17 

physical   constitution  of,  3 

sol  state  of,  4 

structure  of,  10 
Prussak's  space,  of  ear,  15 
Pseudopodium,  16 

Pseudo-stratified  columnar  epithelium,  49 
Pulmonary  artery,  314 
Pulmonary  veins,  317 
Pyloric  glands,  of  stomach,  357 
Pyramidal  cells,  of  brain,  613 

Racemose  glands,  258 
Eanvier's    method    of    staining    nerve 
plexuses  and  endings,  752 


848 


INDEX 


Rathke  ?s  pouchy  of  hypophysis  cerebri, 

572 

Rectum,  379 
Renal  pelvis  and  ureters,  445.    See  also 

Kidney. 

Eep reductive  system,  479 
development  of,  456 
female  organs  of  generation,  507 
external  organs  of,  540 
clitoris,  541 
hymen,  541 

glands  of  Bartholin,  541 
glandulae  vestibulares  minores,  541 
labia  majora,  540 
labia  minora,  540 
vestibule,  540 
mammary  gland,  541 
active,  543 
blood  vessels  of,  547 
colostrum,   546 
glands  of  Montgomery,  545 
lactiferous  duct  of,  542 
lymphatics  of,  547 
milk  of,  547 
resting,  545 

internal  organs  of  generation,  507 
Fallopian  tube,  525 
lymphatics  of,  528 
mucosa  of,  526 
muscular  wall  of,  526 
serous  coat  of,  526 
structure  of,  525 
Graafian     follicle,     resume",     of 

structures,  519 
liquor  folliculi  of,  514 
stratum  granulosum  of,  518 
Pfluger's  tubes,  513 
primitive    follicles    (egg    nests), 

514 

ovarian  follicles,  509 
atresia  of,  514 
corona  radiata  of,  518 
cumulus  oophorus,  518 
development  of,  513 
discus  proligerus  of,  517 
Graafian  follicle,  517 
ovarian  scars,  522 


Reproductive  system,  female  organs  of 
generation,  internal  organs 
of  generation,  o  v  a  r  y, 
507 

blood  supply  of,  523 

corpora  lutea  spuria,  521 

corpora   lutea    vera,    of    preg- 
nancy, 521 

corpus  albicans  of,  510-521 

corpus  hemorrhagicum  of,  519 

corpus  luteum  of,  507-519 

cortex  of,  508 

hilum  of,  508 

lutein  cells  of,  519 

lymphatics  of,  525 

medulla  of,  508 

mesovarium,  507 

nerves  of,  525 

ova,  510 

pampiniform  plexus  of,  523 

tunica  albuginea  of,  510 
oviduct,  525 

blood  supply  of,  527 

lymphatics  of,  528 

mucosa  of,  526 

muscular  coat  of,  526 

structure  of,  525 
ovum,  511 

accessory  nucleus  of,  511 

cytoplasm  of,  511 

deutoplasm  of,  5J1 

nucleus     of      (germinal     spot, 
germinal  vesicle),  511-512 

nuclear  cap,  511 

oocyte,  stage  of,  512 

oogonial,  stage  of,  512 

ootid,  stage  of,  479-512 

vitelline  membrane  of,  511 

vitellus,  511 

yolk  nucleus  of,  511 

zona  pellucida  of,  511 
uterine  cavity,  532 
uterine  glands,  531 
uterus,  528 

blood  vessels  of,  532 

cells  of  Langhans  of  chorionic 
villi,  in,  537 


INDEX 


849 


Reproductive  system,  female  organs  of 
generation,    internal    organs 
of    generation,    uterus,    cer- 
vical glands  of,  532 
chorionic     villi     of     pregnant 

uterus,  .">:',  7 

decidua  menstrualis  of,  534 
decidua  reflexa  of,  537 
decidua  serotina  of,  536 
decidua  vera  of,  537 
decidual  cells  of,  535 
fetal  blood  vessels  in,  538 
gravid,  the,  535 
lymphatics      and      nerves     of, 

533 

menstruating,   533 
mucosa,    or    endometrium,    of, 

529 
muscular    coat    of,     or     myo- 

metrium,  528 

Nabothian  follicles  of,  532 
placenta  uterina,  536 
serous  coat  of,  or  perimetrium, 

528 

structure  of,  528 
vagina,  538 
mucosa  of,  538 
musculature,  538 
outer  fibrous  coat  of,  539 
structure  of,  538 
vestigial  structures,  539 
epoophoron  (parovarium,  organ 

of  Rosenmuller),  539 
hydatid  of   Morgagni    (vesicu- 
lar appendage),  539 
parob'phoron,  540 
fetal,  derivatives  of,  459 
gametogenesis,  460 
chromosomes   in,  464 
determination  of  sex,  475 

chromosomes  in,  476 
diploid    number    of    chromosomes, 

463 

gonad,  460 

haploid  chromosome  group,  464 
heterotypic   division,  460 
maturation,  460 
50 


Reproductive      system,      gametogenesis, 

Mendelian  inheritance,  478 
Mendelism,  477 

determiners  in,  477 
homozygote,  478 
heterozygote,  478    ' 
spermatocytes,  primary,  in,  463 
synapsis  phenomena,  in,  461 
synizesis  in,  463 
telosynapsis  in,  463 
tetrads,  formation  of,  in,  460 
unit  characters  in  heredity,  474 
zygote,  460 

general  considerations  of,  455 
gonads,  or  sex  glands,  456 
male  organs  of  generation,  501 
external  organ,  503 
penis,  503 

corpora  cavernosa  of,  503 
corpus  spongiosum  of,  503-506 
erectile  tissue  of,  503-505 
glands  of  Tyson,  506 
helicine   arteries  of,   504 
pectiniform  septum  of,  504 
lymphatics  of,  506 
nerves  of,  506 
nervi  erigentes  of,  506 
preputial  glands  of,  506 
tunica  albuginea  of,  504 
internal  organs,  479 
Cowper's  glands,  501 
ejaculatory  ducts,  497 
prostate  gland,  497 
blood  supply  of,  500 
structure  of,  497 
prostatic  concretions,  499 
scrotum,  dartos  of,  481 
seminal  vesicles,  495 
testis,  479 

corpus     Highmori      (mediasti- 
num) of,  480 
duct  system  of,  490 
ductuli  efferentes  of,  490 
epididymis  of,  492 
functions  of,  479 
histogenesis  and  structure  of, 
485 


850 


IXDEX 


Reproductive    system,    male    organs    of 
generation,   internal   organs, 
.testis,     interstitial    cells    of 
Leydig,  of,  487 
lipoid  granules  in,  488 
pampiniform  plexus  of,  494 
rete  of,  490 
semen,  486 
spermatic  cord,  494 
Bpermatid,  484 
spermatoblasts,  482 
spermatozoon,  human,  486 
structure  of,  479 
trophocytes   (Sertoli  cells)   of, 

482 

tubules  of,  487 
tubuli  recti  of,  490 
tunica  albuginea  of,  480 
tunica  vaginalis  of,  480 
tunica  vasculosa  of,  480 
vas      (ductus)      deferens      of, 

493 
vestigial     structures,     associated 

with,  502 

appendix  epididymis,  502 
appendix  testis,  502 
ductuli  aberrentes,  502 
paradidymis     (organ     of     Gi- 

raldes),  502 
sinus  pocularis  (sinus  prostati- 

cus),  502 

Miillerian  ducts,  456 
oogenesis,  460-478 
parasynapsis  in,  463 
polar  body  in,  479 
primary  oocyte  in,  478 
secondary  oocyte  in,  479 
sex  chromosome  in,  475 
spermatogenesis,  460 
chromidia  in,  474 
idiozome  in,  475 
prespermatid  in,  474 
spermatogonia  in,  463 
spermatozoon  in,  475 
Wolffian  body,  or  mesonephros,  456 
Wolffian  ducts,  456 
Eesting  nucleus,  24 


Respiratory  system,  292 
development  of,  293 
larynx,  the,  300 

structures  of,  300 

vocal  cords  of,  301 
lung,  the,  304 

alveolar  ducts  of,  310 

alveoli  of,  311 

atria  of,  310 

blood  supply  of,  314-319 

bronchi  of,  304 

bronchial  arteries,  317 

bronchioles  of,  307 

lobule  of,  314 

lymphatics  of,  318 

pleura  of,  312 

pleural  pores  of,  313 

pulmonary  artery,  314 

pulmonary  veins,  317 
nasal  cavity,  293 

blood  vessels  of,  298 

neuroepithelium  of,  297 

olfactory  portion   of,   296 

organ  of  Jacobson,  of,  295 

respiratory  portion  of,  294 

vestibule  of,  293 
nasopharynx,  299 
trachea  of,  302 

Eetia  mirabilia,  of  kidney,  187 
Reticulum,  49-55 

Retina,  arteria  centralis  of,  664-670 
cell  types  of  inner  nuclear  layer  of, 

654 

cones  of,  651 

external  limiting  membrane  of,  (553 
fiber  layer  of,  654 
fibers  of  Miiller,  658 
fovea  centralis  of,  660 
ganglion  cell  layer  of,  657 
general  considerations  of,  644 
inner  nuclear  layer  of,  654 
inner  reticular  layer  of,  656 
inversion  of,  663 
layers  of,  646 
macula  lutea  of,  659 
nerve  fiber  layer  of,  657 
optic  disc  of,  665 


INDEX 


851 


Retina,  optic  papilla  of,  665 

outer  nuclear  layer  of,  654 

outer  reticular  layer  of,  654 

pigment  epithelium  of,  646 

porus  opticus  of,  665 

rod  and  cone  layer  of,  647 

rods  of,  648-658 

and    cones,    development    of,    661- 
663 

supporting  tissues  of,  658 

visual  purple  of,  647-649 

yellow  spot  of,  659 
Einger's  solution,  720 

Safranin  stain,  for  tissues,  744 
Salivary  corpuscles,  243 
Salivary  glands,  390 

blood  supply  of,  392 

lymphatics  of,  393 

nerve  supply  of,  393 

parotid  gland,  390 

sublingual  gland,  392 

submaxillary  gland,  391 
Santorini's  duct,  394 
Sarcoplasm,  90 
Sarcosomes,  of  Retzius,  99 
Scala  media,  of  cochlea,  703 
Scala  tympani,  703 
Scleral  corpuscles,  634 
Sclerotic  coat  of  eye,  634 
Scrotum,  481 
Sectioning  of  tissues,  736 

microtome  for,  736 
Sections,  colloidin  adhesive,   for,  739 

clarification  of,  759 

Mayer's  albumin  for,   739 

mounting,  of,  759 
in  euparal,  761 
in  glycerin  jelly,  760 
in  gum  damar,  760 
in  neutral  balsam,  760 
in  xylol-balsam,  760 
Segmentation  process,  27 
Segmented  spireme,  24 
Semen,  486 

Semicircular  canals,  of  ear,  699 
Seminal  vesicles,  495 


Septum  posticum,  621 
Serous  membranes,  232 
mesothelia  of,  232 
stomata  in,  232 
tunica  propria  of,  232 
Sertoli  cells,  482 

Shrapnell's  membrane,  of  ear,  689 
Sinus  prostaticus,  502 
Sinusoids,  vascular,  187 
Skin,  262 

blood  supply  of,  290 

capillary  layer  of,  268 

cylindrical  cell  layer  of,  264 

derma,  the,  268 

eleidin  layer  of    (stratum  lucidum), 

267 
epidermis,  the,  262 

flattened  cell  layer  and  scaly  layer 

(stratum  corneum)   of,  267 
granular  layer  or  stratum  granu- 

losum,  of,  266 

growth  and  development  of,  270 
hair,  development  of,  277 
mature,  279 
regeneration  of,  286 
root  of,  281 
shaft  of,  281 
sheaths  of,  283 
structure   of,   277 
keratin  of,  267 
layers  of,  262 
nails,  274 

growth  and  development  of,  276 
structure  of,  275 
nerve  supply  of,  291 
prickle  cell  layer  (stratum  spinosum) 

of,  265 

reticular  layer  of,  269 
sebaceous  glands  of,  286 
stratum   germinativum,   265 
sudoriparous  glands  of,  271 
Small    intestine,    374.      See    Digestive 

system. 

Smears,  method  of  making,  730 
Solution,   Hogan's,   721 
normal  saline,  720 
Einger's,  721 


852 


INDEX 


Spaces,  of  Fontana,  643 

Specific  dyes,  740 

Spermatic  cord,  494 

Spermatid,   and  spermatozoon,  484 

Spermatocytes,  primary,  463 

Spermatogenesis,  460 

idiozome  in,  475 

prespermatid  in,  470 
Spermatogonia,  463 
Spermatozoon,   475 

histogenesis,  and  structure  of,  485 

human,  486 
Spinal  cord,  596 

basis  cornu  of,  596 

caput  cornu  of,  596 

cell  column,  of  Clarke,  602 

central  canal  of,  598 

central  commissure  of,  596 

cervical  region,  lower  half  of,  602 

cervical  region,  upper  half  of,  603 

cervix  cornu  of,  596 

columns  of,  598 

filum  terminale  of,  600 

gray  matter  of,  596 

intermediate  zone  of,  596 

lumbar  region  of,  600 

nerve  roots  of,  596 

nucleus  of  Stilling,  of,  602 

regions  of,  599 

segments  of,  596 

sacral  region  of,  600 

thoracic  region  of,  601 

white  matter  of,  598 
Spiral  organ,   of  Corti,   702.     See   also 

Ear. 

Spireme,  loose,  24 
Spleen,  245 

blood  vessels  of,  246 

development  of,  250 

differentiation  of,  from  lymph  nodes, 
249 

functions  of,  249 

pulp  veins  of,  248 
Splenic  cells,  249 
Splenic  nodules,  247 
Spongioblasts,  589 
Spongioplasm,  8 


Staining  methods,  special,  747 

Benda's   mitrochondrial  technic,   757 

blood,  Basting's  eosinate  of  methy- 
lene  blue,  for,  754 

chromaffin  granules,  technic  for,  759 

chromophilic  (tigroid)  granules  in 
cyton  and  dendron,  with 
methylene  blue,  750 

connective  tissue,  Mallory's,  753 
with  picro-fuchsin  (Van  Gieson's), 
752 

cytoplastic  granules,  eosin  and 
methylene  blue  mixture, 
Mann's,  755 

Ehrlich  's  triacid,  755 

elastic  tissue,  Weigert's,   753 

fat,  osmic  acid  for  demonstrating,  758 

glycogen,  Gage's  method  for  demon- 
strating, 758 

medullate  nerve  fibers,  Weigert-Pal 
method  for  demonstrating, 
748 

mitochondria,  757 

mucinous  tissues,  specific,  748 

nerve  cells,  Golgi's,  751 

nerve  plexuses  and  endings,  gold 
chlorid  (Kanvier's)  for,  752 

neurofibrils,  Cajal's,   750 

nitrate    of    silver,    for    cement    sub- 
stances, 752 
Staining  of  tissues,  738 

double,  746 

in  bulk,  739 

progressive,  740 

regressive,  740 
Stains,  aceto-carmin,  744 

alum  carmin,  744 

Auerbach's  fuchsin-methyl-green,  756 

borax  carmin,  743 

carmin,  743 

Congo  red,  746 

Delafield's  hematoxylin,  742 

eosin,  745 

fuchsin,   746 

hematein,  743 
and  eosin,  746 

iron  hematoxylin,  747 


INDEX 


853 


Stains,    Mann's    acid    hematein     (Ehr- 
lich's   hematoxylin),   742 

niethylene  blue,  743 

methyl  blue  and  safranin,  747 

methyl  green,  743 

muchematein,  748 

mucicarmin,  748 

orange  G,  746 

picro-carmin,  744 

safranin,  744 

single,  with  cytoplasmic  dyes,   745 

with  nuclear  dyes,  741 
Stapedius  muscle,  690 
Stapes,  689 
Stenson's  duct,  390 
Stigmata,  38 
Stomach,  353 

blood  supply  of,  360 

cardiac  glands  of,  360 

fundus  glands  of,  354 

lenticular   glands   of,   360 

lymphatics  of,   362 

mucous  coat  of,  353 

muscular  coat  of,  353 

nerve  supply  of,  362 

parietal    cells    (oxyntic    or    delomor- 
phous  cells)  of,  356 

peptic,  or  adelomorphous  cells,  of,  355 

pyloric  glands,  357 

secretion  of,  357 

serous  coat  of,  352 

submucous  coat  of,  353 
Stomata,  38 
Stratified  epithelium,  43 
Stratified  squamous  epithelium,  43 
Stripe  of  Bechterew,  619 
Stripes  of  Baillarger,  619 
Strop,  use  of,  738 
Subarachnoid  space,  621-624 
Subcutaneous  tissue,  269 
Subdural  space,  620-623 
Sublingual  gland,  392 
Submaxillary  gland,  391 
Submucous     plexus      (Meissner 's),     of 

small  intestine,  375. 
Suprarenal  glands,  548 

accessory,  556 


Suprarenal     glands,     chromaffin     gran- 
ules in,  554 

blood  supply  of,  554-555 

development  and  function  of,  548 

lymphatics  and  nerves  of,  556 

medulla,  cells  of,  553 

zona  fasciculata,  552 

zona  glomerulosa,  552 

zona  reticularis,  553 
Sweat  glands,  271 
Sympathetic  plexus,  461-463 
Synapsis  phenomena,  461-463 
Syncytia,  31 

Synizesis  phase  of  gametogenesis,  463 
Synovia,  89 
Synovial  membranes,  232 

Tapetum  cellulosum,  of  eye,  638 
Tapetum  fibrosum,  of  eye,  637 
Tarsus  of  eyelid,  676 
Technic,    for    demonstrating   chromaffin 

granules,  759 
Teeth,  333 

ameloblasts    (adamantoblasts),  333 

cementoblasts,  337 

cementum,  329 

development  of,  336 

deciduous,  331 

dental  enamel,  layers  of,  335 

dental  papilla,  336 

dental  pulp,  323 

dentin  of,  325 

development  of,  330 

enamel  germ  of,  330-331 

enamel  organ,  of,  330 
layers  of,  331 
Tomes'  processes,  333 

odontoclasts,  337 

permanent,  331 

root  membranes  of,  329 

root  canals  of,  336 

Sharpey  's  fibers  in,  329 

structure  of,  323 
Telse  choroidese,  623 
Tellyesniczky 's  fluid,  for  fixation  of 

tissues,    726 
Telophase  of  mitotic  cell  division,  25 


854 


INDEX 


Telosynapsis,  463 
Tendon,  115 

nerve  endings  in,  171 

peritenoneum  of,  115 

vagina  fibrosa,  115 

vagina  mucosa,  115 
Tendon  cells,  117 
Tendon  fasciculi,  115 
Tendon  spindles,  174 
Testis,  479-480 

corpus  Highmori  of,  480 

duct  system  of,  490 

ductuli  efferentes  of,  490 

epididymis,  492 

human,  486 

interstitial  cells,  of  Leydig,  487 

lipoid  granules  in,  488 

mediastinum  of,  480 

rete  of,  490 

semen,  486 

spermatic  cord  of,  494 

spermatid,   and   spermatozoon,   484 

spermatoblasts,  482 

spermatozoon,        histogenesis        and 
structure  of,  485 

trophocytes  of,  482 

tubules  of,  487 

tubuli  recti  of,  490 

tunica  albuginea  of,  480 

tunica  vaginalis  of,  480 

tunica  vasculosa  of,  480 

vas  (ductus)  deferens  of,  493 
Thoracic  duct,  230 
Thrombin,   203 
Thymus  gland,  565 

blood  supply  of,  568 

development  and  function  of,  568 

lymphoid  corpuscles  of,  567 
Thyroid  gland,  557 

accessory,  562 

blood  supply  of,  560 

colloid  in,  557 

development  of,  561 

follfcles  of,  557 

f ollicular  epithelium  of,  559 

function  of,  561 

lymphatics  of,  560 


Thyroid   gland,   nerves  of,   561 

structure  of,  557 
Thyroidin,  561 
Thyroglossal  duct,  343 
Tissue 

adenoid,  64 
adipose,  61 
bone,  72 

compact,  74 

general  consideration  of,  72 
bone  marrow,  77 
cartilage,  67 

blastema  of,  69 

elastic,  71 

fibro-,  71 

hyaline,  68 

matrix  of,  69 

origin  of,  70 

connective,     acidophil     granulocytes, 
52 

areolar,  56 

basophil   granule   cells,  in,   52 

blood  and  nerve  supply  of,  67 

cells  of,  51 

dense  elastic,  60 

dense  fibrous,  59 

elastic  fibers  of,  57 

embryonal,  50-53 

eosinophil  granulocytes  of,  52 

fibrocartilage,  71 

general  statements,  49 

lamellar  cells  of,  52 

loose  fibro-elastic,  56 

marrow,  blood  supply,  78 

mucous,  54 

oxyphil  granulocytes  in,  52 

perichondrium,  72 

periosteum,  74 

plasma  cells  of,  51 

red  marrow,  77 

reticular,  55 

spindle  cells  of,  51 

types  of,  53 

yellow  elastic,  61 
ectoderm,  28 
entoderm,  28 
epithelia,  classification  of,  34 


INDEX 


855 


Tissue,  epithelial  tissue,  30-3 

epithelium,   transitional,   47 
varieties  of,  33 

eruptive,  82 

fat,  61 

stains  for,  62 

intercellular  cement  substance,  in,  30 

lymphatic  corpuscles,  66 

lymphoid,   31-64 

mesoderm,  28 

mucous,  54 

muscular,  90 
Tissue  fixation,  by,  723 

alcohol,  724 

Bouin  's  fluid,  729 

Carnoy's  fluid  (lung),  729 

chromo-acetic-formalin    mixture,    727 

Flemming's  fluid,  728 

formalin,   725 

Gilson's  fluid,  730 

heat,  730 

Kelly's  fluid,  728 

Kleinenberg 's  fluid,  729 

mercuric  chlorid,  725 

mercuro-nitric  mixture,  730 

Miiller's  solution,  726 

Orth's  fluid,  727 

potassium  bichromate,  726 

Tellyesniczky 's  fluid,  726 

vapors,   731 

van  Gehuchten's  fluid,  729 

Zenker's  solution,  727 
Tissue     fixation,    of    human    embryos, 
726 

lung  tissue,  730 
Tissue  juice,  55 
Tissue  staining,  in  bulk,  739 

progressive,  740 

regressive,   740 
Tissue  stains,  744 

aceto-carmin,  744 

alum  carmin,  744 

alum  hematein  (Mayer),  741 

Bohmer's  hematoxylin,  741 

borax  carmin,  743 

carmin,  743 

double  staining,  746 


Tissue   stains,  Congo  red,  746 
Delafield  'a  hematoxylin,  742 
eosin,  745 
fuchsin,   746 
hematin,   741-743 

and  eosin,  746 
iron-hematoxylin,  747 
Mallory's,      for      connective      tissue, 

753 

Mann's    hematein     (Ehrlich's    hema- 
toxylin^, 742 
methyl  green,  743 
methyl  blue,  and  safranin,  747 
methylene  blue,  743 
muchematein,  748 
mucicarmin,  748 
mucinous,  specific  stain,  748 
orange  G,  746 
picro-carmin,  744 
picro-fuchsin,    for    connective    tissue 

(Van  Gieson),  752 
safranin,  744 

single,  with  nuclear  dyes,  741 
Weigert's,  for  elastic  tissue,  731 
Tissues,  30 

box  for  embedding  for  sectioning  of 

737 

decalcification  of,  731 
dissociation  of,  721 

chemical,  722 
embedding  of,  734 

in  celloidin,  734 

in  paraffin,  735 
hardening  of,  733 
injection  of,  732 
maceration  of,  721 
sectioning  of,  736 
staining  of,  738 
teasing  of,  721 
Tongue,  337 
blood  vessels  of,  343 
foramen  cecum  of,  343 
glands  of,  342 
lymphatics  of,  344 
mucous  membrane  of,  337 
nerve  supply  of,  344 
papillse  of,  339 


856 


INDEX 


Tongue,  serous  glands  of,  343 

taste  buds  of,  341 
Tonsil,  faucial  (palatine),  242 

lingual,  244,  343 

pharyngeal,  244 

tubal,  692 
Trachea,  302 

structures  of,  302 
Tunica  propria,  corium  of  skin,  34 
Tympanic  membrane,  687 
Tympanum     of     ear,     685.       See     also 

ear 
Tyson's  glands,  in  penis,  506 

Umbo,  of  tympanic  membrane,  687 
Unit   characters,    in    Mendelian   inheri- 
tance, 477 
Urinary  system,  423 
kidney,  423 

arciform  veins  of,  443 

arteries,    arteriae    proprise    renales, 

440 

arciform,  440 
arteriae  rectae,  441 
interlobular,  441 
Bellini's  ducts  of,  438 
capsule  of  Bowman,  of,  429 
corpuscles  (renal)  of,  425 
cortex  of,  424 
glomerulus  of,  429 
lymphatics  and  nerves  of,  444 
medulla  of,  424 
papillary  ducts  of,  438 
pelvis  and  ureter  of,  445 
blood  supply  of,  448 
mucosa  of,  445 
muscular  coat  of,  448 
tunica  propria  of,  447 
renal    circulation,     table     showing 

course  of,  443 
renal  connective  tissue,  426 
renal  corpuscles    (Malpighian  bod- 
ies), 425-429 
renal  lobule,  426 
topography  of,  423 
tubules      of,      arched      connecting 
(functional  tubule),  437 


Urinary    system,    kidney,    tubules    of, 
ascending    limb    of    Henle's 
loop,   435 
descending  limb  of  Henle's  loop, 

434 

distal  convoluted  portion  of,  436 
divisions  of  renal  tubule,  429 
loop  of  Henle,  435 
neck  of,  431 
peculiarities  of,  440 
proximal   convoluted   portion   of, 

431 

straight  collecting,  437 
table   of    divisions   of    renal   tu- 
bule, 439 

uriniferous,  or  renal,  427 
urethra,  female,  452 
structure  of,  452 
urethra,  male,  structure  of,  454 
urinary  bladder,  448 

mucous  membrane  of,  448 

muscular  coat  of,  451 

vascular    and    nerve    supply    of; 

452 

veins  of,  stellate,  443 
vena?  propriae  renales,  443 
venulse  rectee  of,  443 

Uterus,  the,  532 

blood  vessels  of,  532 

cells  of  Langhans  of   chorionic  villi 

of,  537 

cervical  glands  of,  532 
chorionic  villi  of  pregnant  uterus,  537 
decidua  menstrualis  of,  534 
decidua  reflexa  of,  537 
decidua  serotina  of,  536 
decidua  vera  of,  537 
decidual  cells  of,  535 
fetal  blood  vessels,  538 
glands  of,  531 
gravid,  535 

lymphatics  and  nerves  of,  533 
menstruating,  533 
mucosa,  or  endometrium,  of,  529 
muscular    coat,    or    myometrium,    of, 

528 


INDEX 


857 


Uterus,  Nabothian   follicles  of,  532 

placenta  uterina,  536 

serous  coat,  or  perimetrium,  of,  528 

structure  of,  528 
Utricle,  of  ear,  698 

Vagina,  mucosa  of,  538 

musculature  of,  538 

outer  fibrous  coat  of,  539 

structure  of,  538 
Valves,  of  heart,  196 
Valvulae  conniventes,  364 
Yas  (ductus)  deferens,  493 
Vascular  sinusoids,   187 
Vascular  tissue,  176 
Veins,  187 

arciform,  of  kidney,  443 

atypical,  189 

auditory,  716 

circulus  venosus,  of  Haller,  547 

cranial,  190 

larger,  structure  of,  188 

of  central  nervous  system,  625 

of  ear,  715 

of  kidney,  443 

of  liver,  415 

of  ovary,  523 

of  sclera,  635 

of  spermatic  cord,  494 

portal,  417 

pulmonary,  190-317 

small,  188 

smaller    and    larger,    comparison    of, 
190 


Veins,  valves  in,  191 

vena  cava,  190 

vena  conies,  191 

venae  vorticosae,  of  eye,  672 
Velum,  marginal,  590 
Venous  spaces,  190 
Venules,  precapillary,  187 
Vermiform  appendix,  379 
Vesicular  appendages,  539 
Vestibule,  of  pudendum,  540 
Vestigial     structures,     associated     with 
reproductive     organs,     539- 
540 

Visual  area,  617 
Visual  axis,  628 
Vitreous  humor,  669 
Vocal  cords,  301 


Weigert-Pal      stain,      for      medullated 

nerve  fibers,  748 

Weigert's  elastic  tissue  stain,  753 
Wirsung's  duct,  394 
Wolffian  body,  or  mesonephros,  456 


Xylo-balsam,     for     mounting     sections, 
760 


Zenker's  solution,  727 
Zimmermann's  technic,  for  intercalated 
discs  of  cardiac  muscle,  758 
Zonula  ciliaris,  of  eye,  670 
Zygote,  27-460 


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